summaryrefslogtreecommitdiff
path: root/refs/files-backend.c
blob: fec77744b40179b1454093bd37cf0815f3b755ae (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
3069
3070
3071
3072
3073
3074
3075
3076
3077
3078
#include "../cache.h"
#include "../config.h"
#include "../refs.h"
#include "refs-internal.h"
#include "ref-cache.h"
#include "packed-backend.h"
#include "../iterator.h"
#include "../dir-iterator.h"
#include "../lockfile.h"
#include "../object.h"
#include "../dir.h"

struct ref_lock {
	char *ref_name;
	struct lock_file lk;
	struct object_id old_oid;
};

/*
 * Future: need to be in "struct repository"
 * when doing a full libification.
 */
struct files_ref_store {
	struct ref_store base;
	unsigned int store_flags;

	char *gitdir;
	char *gitcommondir;

	struct ref_cache *loose;

	struct ref_store *packed_ref_store;
};

static void clear_loose_ref_cache(struct files_ref_store *refs)
{
	if (refs->loose) {
		free_ref_cache(refs->loose);
		refs->loose = NULL;
	}
}

/*
 * Create a new submodule ref cache and add it to the internal
 * set of caches.
 */
static struct ref_store *files_ref_store_create(const char *gitdir,
						unsigned int flags)
{
	struct files_ref_store *refs = xcalloc(1, sizeof(*refs));
	struct ref_store *ref_store = (struct ref_store *)refs;
	struct strbuf sb = STRBUF_INIT;

	base_ref_store_init(ref_store, &refs_be_files);
	refs->store_flags = flags;

	refs->gitdir = xstrdup(gitdir);
	get_common_dir_noenv(&sb, gitdir);
	refs->gitcommondir = strbuf_detach(&sb, NULL);
	strbuf_addf(&sb, "%s/packed-refs", refs->gitcommondir);
	refs->packed_ref_store = packed_ref_store_create(sb.buf, flags);
	strbuf_release(&sb);

	return ref_store;
}

/*
 * Die if refs is not the main ref store. caller is used in any
 * necessary error messages.
 */
static void files_assert_main_repository(struct files_ref_store *refs,
					 const char *caller)
{
	if (refs->store_flags & REF_STORE_MAIN)
		return;

	die("BUG: operation %s only allowed for main ref store", caller);
}

/*
 * Downcast ref_store to files_ref_store. Die if ref_store is not a
 * files_ref_store. required_flags is compared with ref_store's
 * store_flags to ensure the ref_store has all required capabilities.
 * "caller" is used in any necessary error messages.
 */
static struct files_ref_store *files_downcast(struct ref_store *ref_store,
					      unsigned int required_flags,
					      const char *caller)
{
	struct files_ref_store *refs;

	if (ref_store->be != &refs_be_files)
		die("BUG: ref_store is type \"%s\" not \"files\" in %s",
		    ref_store->be->name, caller);

	refs = (struct files_ref_store *)ref_store;

	if ((refs->store_flags & required_flags) != required_flags)
		die("BUG: operation %s requires abilities 0x%x, but only have 0x%x",
		    caller, required_flags, refs->store_flags);

	return refs;
}

static void files_reflog_path(struct files_ref_store *refs,
			      struct strbuf *sb,
			      const char *refname)
{
	switch (ref_type(refname)) {
	case REF_TYPE_PER_WORKTREE:
	case REF_TYPE_PSEUDOREF:
		strbuf_addf(sb, "%s/logs/%s", refs->gitdir, refname);
		break;
	case REF_TYPE_NORMAL:
		strbuf_addf(sb, "%s/logs/%s", refs->gitcommondir, refname);
		break;
	default:
		die("BUG: unknown ref type %d of ref %s",
		    ref_type(refname), refname);
	}
}

static void files_ref_path(struct files_ref_store *refs,
			   struct strbuf *sb,
			   const char *refname)
{
	switch (ref_type(refname)) {
	case REF_TYPE_PER_WORKTREE:
	case REF_TYPE_PSEUDOREF:
		strbuf_addf(sb, "%s/%s", refs->gitdir, refname);
		break;
	case REF_TYPE_NORMAL:
		strbuf_addf(sb, "%s/%s", refs->gitcommondir, refname);
		break;
	default:
		die("BUG: unknown ref type %d of ref %s",
		    ref_type(refname), refname);
	}
}

/*
 * Read the loose references from the namespace dirname into dir
 * (without recursing).  dirname must end with '/'.  dir must be the
 * directory entry corresponding to dirname.
 */
static void loose_fill_ref_dir(struct ref_store *ref_store,
			       struct ref_dir *dir, const char *dirname)
{
	struct files_ref_store *refs =
		files_downcast(ref_store, REF_STORE_READ, "fill_ref_dir");
	DIR *d;
	struct dirent *de;
	int dirnamelen = strlen(dirname);
	struct strbuf refname;
	struct strbuf path = STRBUF_INIT;
	size_t path_baselen;

	files_ref_path(refs, &path, dirname);
	path_baselen = path.len;

	d = opendir(path.buf);
	if (!d) {
		strbuf_release(&path);
		return;
	}

	strbuf_init(&refname, dirnamelen + 257);
	strbuf_add(&refname, dirname, dirnamelen);

	while ((de = readdir(d)) != NULL) {
		struct object_id oid;
		struct stat st;
		int flag;

		if (de->d_name[0] == '.')
			continue;
		if (ends_with(de->d_name, ".lock"))
			continue;
		strbuf_addstr(&refname, de->d_name);
		strbuf_addstr(&path, de->d_name);
		if (stat(path.buf, &st) < 0) {
			; /* silently ignore */
		} else if (S_ISDIR(st.st_mode)) {
			strbuf_addch(&refname, '/');
			add_entry_to_dir(dir,
					 create_dir_entry(dir->cache, refname.buf,
							  refname.len, 1));
		} else {
			if (!refs_resolve_ref_unsafe(&refs->base,
						     refname.buf,
						     RESOLVE_REF_READING,
						     oid.hash, &flag)) {
				oidclr(&oid);
				flag |= REF_ISBROKEN;
			} else if (is_null_oid(&oid)) {
				/*
				 * It is so astronomically unlikely
				 * that NULL_SHA1 is the SHA-1 of an
				 * actual object that we consider its
				 * appearance in a loose reference
				 * file to be repo corruption
				 * (probably due to a software bug).
				 */
				flag |= REF_ISBROKEN;
			}

			if (check_refname_format(refname.buf,
						 REFNAME_ALLOW_ONELEVEL)) {
				if (!refname_is_safe(refname.buf))
					die("loose refname is dangerous: %s", refname.buf);
				oidclr(&oid);
				flag |= REF_BAD_NAME | REF_ISBROKEN;
			}
			add_entry_to_dir(dir,
					 create_ref_entry(refname.buf, &oid, flag));
		}
		strbuf_setlen(&refname, dirnamelen);
		strbuf_setlen(&path, path_baselen);
	}
	strbuf_release(&refname);
	strbuf_release(&path);
	closedir(d);

	/*
	 * Manually add refs/bisect, which, being per-worktree, might
	 * not appear in the directory listing for refs/ in the main
	 * repo.
	 */
	if (!strcmp(dirname, "refs/")) {
		int pos = search_ref_dir(dir, "refs/bisect/", 12);

		if (pos < 0) {
			struct ref_entry *child_entry = create_dir_entry(
					dir->cache, "refs/bisect/", 12, 1);
			add_entry_to_dir(dir, child_entry);
		}
	}
}

static struct ref_cache *get_loose_ref_cache(struct files_ref_store *refs)
{
	if (!refs->loose) {
		/*
		 * Mark the top-level directory complete because we
		 * are about to read the only subdirectory that can
		 * hold references:
		 */
		refs->loose = create_ref_cache(&refs->base, loose_fill_ref_dir);

		/* We're going to fill the top level ourselves: */
		refs->loose->root->flag &= ~REF_INCOMPLETE;

		/*
		 * Add an incomplete entry for "refs/" (to be filled
		 * lazily):
		 */
		add_entry_to_dir(get_ref_dir(refs->loose->root),
				 create_dir_entry(refs->loose, "refs/", 5, 1));
	}
	return refs->loose;
}

static int files_read_raw_ref(struct ref_store *ref_store,
			      const char *refname, unsigned char *sha1,
			      struct strbuf *referent, unsigned int *type)
{
	struct files_ref_store *refs =
		files_downcast(ref_store, REF_STORE_READ, "read_raw_ref");
	struct strbuf sb_contents = STRBUF_INIT;
	struct strbuf sb_path = STRBUF_INIT;
	const char *path;
	const char *buf;
	struct stat st;
	int fd;
	int ret = -1;
	int save_errno;
	int remaining_retries = 3;

	*type = 0;
	strbuf_reset(&sb_path);

	files_ref_path(refs, &sb_path, refname);

	path = sb_path.buf;

stat_ref:
	/*
	 * We might have to loop back here to avoid a race
	 * condition: first we lstat() the file, then we try
	 * to read it as a link or as a file.  But if somebody
	 * changes the type of the file (file <-> directory
	 * <-> symlink) between the lstat() and reading, then
	 * we don't want to report that as an error but rather
	 * try again starting with the lstat().
	 *
	 * We'll keep a count of the retries, though, just to avoid
	 * any confusing situation sending us into an infinite loop.
	 */

	if (remaining_retries-- <= 0)
		goto out;

	if (lstat(path, &st) < 0) {
		if (errno != ENOENT)
			goto out;
		if (refs_read_raw_ref(refs->packed_ref_store, refname,
				      sha1, referent, type)) {
			errno = ENOENT;
			goto out;
		}
		ret = 0;
		goto out;
	}

	/* Follow "normalized" - ie "refs/.." symlinks by hand */
	if (S_ISLNK(st.st_mode)) {
		strbuf_reset(&sb_contents);
		if (strbuf_readlink(&sb_contents, path, 0) < 0) {
			if (errno == ENOENT || errno == EINVAL)
				/* inconsistent with lstat; retry */
				goto stat_ref;
			else
				goto out;
		}
		if (starts_with(sb_contents.buf, "refs/") &&
		    !check_refname_format(sb_contents.buf, 0)) {
			strbuf_swap(&sb_contents, referent);
			*type |= REF_ISSYMREF;
			ret = 0;
			goto out;
		}
		/*
		 * It doesn't look like a refname; fall through to just
		 * treating it like a non-symlink, and reading whatever it
		 * points to.
		 */
	}

	/* Is it a directory? */
	if (S_ISDIR(st.st_mode)) {
		/*
		 * Even though there is a directory where the loose
		 * ref is supposed to be, there could still be a
		 * packed ref:
		 */
		if (refs_read_raw_ref(refs->packed_ref_store, refname,
				      sha1, referent, type)) {
			errno = EISDIR;
			goto out;
		}
		ret = 0;
		goto out;
	}

	/*
	 * Anything else, just open it and try to use it as
	 * a ref
	 */
	fd = open(path, O_RDONLY);
	if (fd < 0) {
		if (errno == ENOENT && !S_ISLNK(st.st_mode))
			/* inconsistent with lstat; retry */
			goto stat_ref;
		else
			goto out;
	}
	strbuf_reset(&sb_contents);
	if (strbuf_read(&sb_contents, fd, 256) < 0) {
		int save_errno = errno;
		close(fd);
		errno = save_errno;
		goto out;
	}
	close(fd);
	strbuf_rtrim(&sb_contents);
	buf = sb_contents.buf;
	if (starts_with(buf, "ref:")) {
		buf += 4;
		while (isspace(*buf))
			buf++;

		strbuf_reset(referent);
		strbuf_addstr(referent, buf);
		*type |= REF_ISSYMREF;
		ret = 0;
		goto out;
	}

	/*
	 * Please note that FETCH_HEAD has additional
	 * data after the sha.
	 */
	if (get_sha1_hex(buf, sha1) ||
	    (buf[40] != '\0' && !isspace(buf[40]))) {
		*type |= REF_ISBROKEN;
		errno = EINVAL;
		goto out;
	}

	ret = 0;

out:
	save_errno = errno;
	strbuf_release(&sb_path);
	strbuf_release(&sb_contents);
	errno = save_errno;
	return ret;
}

static void unlock_ref(struct ref_lock *lock)
{
	rollback_lock_file(&lock->lk);
	free(lock->ref_name);
	free(lock);
}

/*
 * Lock refname, without following symrefs, and set *lock_p to point
 * at a newly-allocated lock object. Fill in lock->old_oid, referent,
 * and type similarly to read_raw_ref().
 *
 * The caller must verify that refname is a "safe" reference name (in
 * the sense of refname_is_safe()) before calling this function.
 *
 * If the reference doesn't already exist, verify that refname doesn't
 * have a D/F conflict with any existing references. extras and skip
 * are passed to refs_verify_refname_available() for this check.
 *
 * If mustexist is not set and the reference is not found or is
 * broken, lock the reference anyway but clear sha1.
 *
 * Return 0 on success. On failure, write an error message to err and
 * return TRANSACTION_NAME_CONFLICT or TRANSACTION_GENERIC_ERROR.
 *
 * Implementation note: This function is basically
 *
 *     lock reference
 *     read_raw_ref()
 *
 * but it includes a lot more code to
 * - Deal with possible races with other processes
 * - Avoid calling refs_verify_refname_available() when it can be
 *   avoided, namely if we were successfully able to read the ref
 * - Generate informative error messages in the case of failure
 */
static int lock_raw_ref(struct files_ref_store *refs,
			const char *refname, int mustexist,
			const struct string_list *extras,
			const struct string_list *skip,
			struct ref_lock **lock_p,
			struct strbuf *referent,
			unsigned int *type,
			struct strbuf *err)
{
	struct ref_lock *lock;
	struct strbuf ref_file = STRBUF_INIT;
	int attempts_remaining = 3;
	int ret = TRANSACTION_GENERIC_ERROR;

	assert(err);
	files_assert_main_repository(refs, "lock_raw_ref");

	*type = 0;

	/* First lock the file so it can't change out from under us. */

	*lock_p = lock = xcalloc(1, sizeof(*lock));

	lock->ref_name = xstrdup(refname);
	files_ref_path(refs, &ref_file, refname);

retry:
	switch (safe_create_leading_directories(ref_file.buf)) {
	case SCLD_OK:
		break; /* success */
	case SCLD_EXISTS:
		/*
		 * Suppose refname is "refs/foo/bar". We just failed
		 * to create the containing directory, "refs/foo",
		 * because there was a non-directory in the way. This
		 * indicates a D/F conflict, probably because of
		 * another reference such as "refs/foo". There is no
		 * reason to expect this error to be transitory.
		 */
		if (refs_verify_refname_available(&refs->base, refname,
						  extras, skip, err)) {
			if (mustexist) {
				/*
				 * To the user the relevant error is
				 * that the "mustexist" reference is
				 * missing:
				 */
				strbuf_reset(err);
				strbuf_addf(err, "unable to resolve reference '%s'",
					    refname);
			} else {
				/*
				 * The error message set by
				 * refs_verify_refname_available() is
				 * OK.
				 */
				ret = TRANSACTION_NAME_CONFLICT;
			}
		} else {
			/*
			 * The file that is in the way isn't a loose
			 * reference. Report it as a low-level
			 * failure.
			 */
			strbuf_addf(err, "unable to create lock file %s.lock; "
				    "non-directory in the way",
				    ref_file.buf);
		}
		goto error_return;
	case SCLD_VANISHED:
		/* Maybe another process was tidying up. Try again. */
		if (--attempts_remaining > 0)
			goto retry;
		/* fall through */
	default:
		strbuf_addf(err, "unable to create directory for %s",
			    ref_file.buf);
		goto error_return;
	}

	if (hold_lock_file_for_update_timeout(
			    &lock->lk, ref_file.buf, LOCK_NO_DEREF,
			    get_files_ref_lock_timeout_ms()) < 0) {
		if (errno == ENOENT && --attempts_remaining > 0) {
			/*
			 * Maybe somebody just deleted one of the
			 * directories leading to ref_file.  Try
			 * again:
			 */
			goto retry;
		} else {
			unable_to_lock_message(ref_file.buf, errno, err);
			goto error_return;
		}
	}

	/*
	 * Now we hold the lock and can read the reference without
	 * fear that its value will change.
	 */

	if (files_read_raw_ref(&refs->base, refname,
			       lock->old_oid.hash, referent, type)) {
		if (errno == ENOENT) {
			if (mustexist) {
				/* Garden variety missing reference. */
				strbuf_addf(err, "unable to resolve reference '%s'",
					    refname);
				goto error_return;
			} else {
				/*
				 * Reference is missing, but that's OK. We
				 * know that there is not a conflict with
				 * another loose reference because
				 * (supposing that we are trying to lock
				 * reference "refs/foo/bar"):
				 *
				 * - We were successfully able to create
				 *   the lockfile refs/foo/bar.lock, so we
				 *   know there cannot be a loose reference
				 *   named "refs/foo".
				 *
				 * - We got ENOENT and not EISDIR, so we
				 *   know that there cannot be a loose
				 *   reference named "refs/foo/bar/baz".
				 */
			}
		} else if (errno == EISDIR) {
			/*
			 * There is a directory in the way. It might have
			 * contained references that have been deleted. If
			 * we don't require that the reference already
			 * exists, try to remove the directory so that it
			 * doesn't cause trouble when we want to rename the
			 * lockfile into place later.
			 */
			if (mustexist) {
				/* Garden variety missing reference. */
				strbuf_addf(err, "unable to resolve reference '%s'",
					    refname);
				goto error_return;
			} else if (remove_dir_recursively(&ref_file,
							  REMOVE_DIR_EMPTY_ONLY)) {
				if (refs_verify_refname_available(
						    &refs->base, refname,
						    extras, skip, err)) {
					/*
					 * The error message set by
					 * verify_refname_available() is OK.
					 */
					ret = TRANSACTION_NAME_CONFLICT;
					goto error_return;
				} else {
					/*
					 * We can't delete the directory,
					 * but we also don't know of any
					 * references that it should
					 * contain.
					 */
					strbuf_addf(err, "there is a non-empty directory '%s' "
						    "blocking reference '%s'",
						    ref_file.buf, refname);
					goto error_return;
				}
			}
		} else if (errno == EINVAL && (*type & REF_ISBROKEN)) {
			strbuf_addf(err, "unable to resolve reference '%s': "
				    "reference broken", refname);
			goto error_return;
		} else {
			strbuf_addf(err, "unable to resolve reference '%s': %s",
				    refname, strerror(errno));
			goto error_return;
		}

		/*
		 * If the ref did not exist and we are creating it,
		 * make sure there is no existing packed ref that
		 * conflicts with refname:
		 */
		if (refs_verify_refname_available(
				    refs->packed_ref_store, refname,
				    extras, skip, err))
			goto error_return;
	}

	ret = 0;
	goto out;

error_return:
	unlock_ref(lock);
	*lock_p = NULL;

out:
	strbuf_release(&ref_file);
	return ret;
}

static int files_peel_ref(struct ref_store *ref_store,
			  const char *refname, unsigned char *sha1)
{
	struct files_ref_store *refs =
		files_downcast(ref_store, REF_STORE_READ | REF_STORE_ODB,
			       "peel_ref");
	int flag;
	unsigned char base[20];

	if (current_ref_iter && current_ref_iter->refname == refname) {
		struct object_id peeled;

		if (ref_iterator_peel(current_ref_iter, &peeled))
			return -1;
		hashcpy(sha1, peeled.hash);
		return 0;
	}

	if (refs_read_ref_full(ref_store, refname,
			       RESOLVE_REF_READING, base, &flag))
		return -1;

	/*
	 * If the reference is packed, read its ref_entry from the
	 * cache in the hope that we already know its peeled value.
	 * We only try this optimization on packed references because
	 * (a) forcing the filling of the loose reference cache could
	 * be expensive and (b) loose references anyway usually do not
	 * have REF_KNOWS_PEELED.
	 */
	if (flag & REF_ISPACKED &&
	    !refs_peel_ref(refs->packed_ref_store, refname, sha1))
		return 0;

	return peel_object(base, sha1);
}

struct files_ref_iterator {
	struct ref_iterator base;

	struct ref_iterator *iter0;
	unsigned int flags;
};

static int files_ref_iterator_advance(struct ref_iterator *ref_iterator)
{
	struct files_ref_iterator *iter =
		(struct files_ref_iterator *)ref_iterator;
	int ok;

	while ((ok = ref_iterator_advance(iter->iter0)) == ITER_OK) {
		if (iter->flags & DO_FOR_EACH_PER_WORKTREE_ONLY &&
		    ref_type(iter->iter0->refname) != REF_TYPE_PER_WORKTREE)
			continue;

		if (!(iter->flags & DO_FOR_EACH_INCLUDE_BROKEN) &&
		    !ref_resolves_to_object(iter->iter0->refname,
					    iter->iter0->oid,
					    iter->iter0->flags))
			continue;

		iter->base.refname = iter->iter0->refname;
		iter->base.oid = iter->iter0->oid;
		iter->base.flags = iter->iter0->flags;
		return ITER_OK;
	}

	iter->iter0 = NULL;
	if (ref_iterator_abort(ref_iterator) != ITER_DONE)
		ok = ITER_ERROR;

	return ok;
}

static int files_ref_iterator_peel(struct ref_iterator *ref_iterator,
				   struct object_id *peeled)
{
	struct files_ref_iterator *iter =
		(struct files_ref_iterator *)ref_iterator;

	return ref_iterator_peel(iter->iter0, peeled);
}

static int files_ref_iterator_abort(struct ref_iterator *ref_iterator)
{
	struct files_ref_iterator *iter =
		(struct files_ref_iterator *)ref_iterator;
	int ok = ITER_DONE;

	if (iter->iter0)
		ok = ref_iterator_abort(iter->iter0);

	base_ref_iterator_free(ref_iterator);
	return ok;
}

static struct ref_iterator_vtable files_ref_iterator_vtable = {
	files_ref_iterator_advance,
	files_ref_iterator_peel,
	files_ref_iterator_abort
};

static struct ref_iterator *files_ref_iterator_begin(
		struct ref_store *ref_store,
		const char *prefix, unsigned int flags)
{
	struct files_ref_store *refs;
	struct ref_iterator *loose_iter, *packed_iter;
	struct files_ref_iterator *iter;
	struct ref_iterator *ref_iterator;
	unsigned int required_flags = REF_STORE_READ;

	if (!(flags & DO_FOR_EACH_INCLUDE_BROKEN))
		required_flags |= REF_STORE_ODB;

	refs = files_downcast(ref_store, required_flags, "ref_iterator_begin");

	iter = xcalloc(1, sizeof(*iter));
	ref_iterator = &iter->base;
	base_ref_iterator_init(ref_iterator, &files_ref_iterator_vtable);

	/*
	 * We must make sure that all loose refs are read before
	 * accessing the packed-refs file; this avoids a race
	 * condition if loose refs are migrated to the packed-refs
	 * file by a simultaneous process, but our in-memory view is
	 * from before the migration. We ensure this as follows:
	 * First, we call start the loose refs iteration with its
	 * `prime_ref` argument set to true. This causes the loose
	 * references in the subtree to be pre-read into the cache.
	 * (If they've already been read, that's OK; we only need to
	 * guarantee that they're read before the packed refs, not
	 * *how much* before.) After that, we call
	 * packed_ref_iterator_begin(), which internally checks
	 * whether the packed-ref cache is up to date with what is on
	 * disk, and re-reads it if not.
	 */

	loose_iter = cache_ref_iterator_begin(get_loose_ref_cache(refs),
					      prefix, 1);

	/*
	 * The packed-refs file might contain broken references, for
	 * example an old version of a reference that points at an
	 * object that has since been garbage-collected. This is OK as
	 * long as there is a corresponding loose reference that
	 * overrides it, and we don't want to emit an error message in
	 * this case. So ask the packed_ref_store for all of its
	 * references, and (if needed) do our own check for broken
	 * ones in files_ref_iterator_advance(), after we have merged
	 * the packed and loose references.
	 */
	packed_iter = refs_ref_iterator_begin(
			refs->packed_ref_store, prefix, 0,
			DO_FOR_EACH_INCLUDE_BROKEN);

	iter->iter0 = overlay_ref_iterator_begin(loose_iter, packed_iter);
	iter->flags = flags;

	return ref_iterator;
}

/*
 * Verify that the reference locked by lock has the value old_sha1.
 * Fail if the reference doesn't exist and mustexist is set. Return 0
 * on success. On error, write an error message to err, set errno, and
 * return a negative value.
 */
static int verify_lock(struct ref_store *ref_store, struct ref_lock *lock,
		       const unsigned char *old_sha1, int mustexist,
		       struct strbuf *err)
{
	assert(err);

	if (refs_read_ref_full(ref_store, lock->ref_name,
			       mustexist ? RESOLVE_REF_READING : 0,
			       lock->old_oid.hash, NULL)) {
		if (old_sha1) {
			int save_errno = errno;
			strbuf_addf(err, "can't verify ref '%s'", lock->ref_name);
			errno = save_errno;
			return -1;
		} else {
			oidclr(&lock->old_oid);
			return 0;
		}
	}
	if (old_sha1 && hashcmp(lock->old_oid.hash, old_sha1)) {
		strbuf_addf(err, "ref '%s' is at %s but expected %s",
			    lock->ref_name,
			    oid_to_hex(&lock->old_oid),
			    sha1_to_hex(old_sha1));
		errno = EBUSY;
		return -1;
	}
	return 0;
}

static int remove_empty_directories(struct strbuf *path)
{
	/*
	 * we want to create a file but there is a directory there;
	 * if that is an empty directory (or a directory that contains
	 * only empty directories), remove them.
	 */
	return remove_dir_recursively(path, REMOVE_DIR_EMPTY_ONLY);
}

static int create_reflock(const char *path, void *cb)
{
	struct lock_file *lk = cb;

	return hold_lock_file_for_update_timeout(
			lk, path, LOCK_NO_DEREF,
			get_files_ref_lock_timeout_ms()) < 0 ? -1 : 0;
}

/*
 * Locks a ref returning the lock on success and NULL on failure.
 * On failure errno is set to something meaningful.
 */
static struct ref_lock *lock_ref_sha1_basic(struct files_ref_store *refs,
					    const char *refname,
					    const unsigned char *old_sha1,
					    const struct string_list *extras,
					    const struct string_list *skip,
					    unsigned int flags, int *type,
					    struct strbuf *err)
{
	struct strbuf ref_file = STRBUF_INIT;
	struct ref_lock *lock;
	int last_errno = 0;
	int mustexist = (old_sha1 && !is_null_sha1(old_sha1));
	int resolve_flags = RESOLVE_REF_NO_RECURSE;
	int resolved;

	files_assert_main_repository(refs, "lock_ref_sha1_basic");
	assert(err);

	lock = xcalloc(1, sizeof(struct ref_lock));

	if (mustexist)
		resolve_flags |= RESOLVE_REF_READING;
	if (flags & REF_DELETING)
		resolve_flags |= RESOLVE_REF_ALLOW_BAD_NAME;

	files_ref_path(refs, &ref_file, refname);
	resolved = !!refs_resolve_ref_unsafe(&refs->base,
					     refname, resolve_flags,
					     lock->old_oid.hash, type);
	if (!resolved && errno == EISDIR) {
		/*
		 * we are trying to lock foo but we used to
		 * have foo/bar which now does not exist;
		 * it is normal for the empty directory 'foo'
		 * to remain.
		 */
		if (remove_empty_directories(&ref_file)) {
			last_errno = errno;
			if (!refs_verify_refname_available(
					    &refs->base,
					    refname, extras, skip, err))
				strbuf_addf(err, "there are still refs under '%s'",
					    refname);
			goto error_return;
		}
		resolved = !!refs_resolve_ref_unsafe(&refs->base,
						     refname, resolve_flags,
						     lock->old_oid.hash, type);
	}
	if (!resolved) {
		last_errno = errno;
		if (last_errno != ENOTDIR ||
		    !refs_verify_refname_available(&refs->base, refname,
						   extras, skip, err))
			strbuf_addf(err, "unable to resolve reference '%s': %s",
				    refname, strerror(last_errno));

		goto error_return;
	}

	/*
	 * If the ref did not exist and we are creating it, make sure
	 * there is no existing packed ref whose name begins with our
	 * refname, nor a packed ref whose name is a proper prefix of
	 * our refname.
	 */
	if (is_null_oid(&lock->old_oid) &&
	    refs_verify_refname_available(refs->packed_ref_store, refname,
					  extras, skip, err)) {
		last_errno = ENOTDIR;
		goto error_return;
	}

	lock->ref_name = xstrdup(refname);

	if (raceproof_create_file(ref_file.buf, create_reflock, &lock->lk)) {
		last_errno = errno;
		unable_to_lock_message(ref_file.buf, errno, err);
		goto error_return;
	}

	if (verify_lock(&refs->base, lock, old_sha1, mustexist, err)) {
		last_errno = errno;
		goto error_return;
	}
	goto out;

 error_return:
	unlock_ref(lock);
	lock = NULL;

 out:
	strbuf_release(&ref_file);
	errno = last_errno;
	return lock;
}

struct ref_to_prune {
	struct ref_to_prune *next;
	unsigned char sha1[20];
	char name[FLEX_ARRAY];
};

enum {
	REMOVE_EMPTY_PARENTS_REF = 0x01,
	REMOVE_EMPTY_PARENTS_REFLOG = 0x02
};

/*
 * Remove empty parent directories associated with the specified
 * reference and/or its reflog, but spare [logs/]refs/ and immediate
 * subdirs. flags is a combination of REMOVE_EMPTY_PARENTS_REF and/or
 * REMOVE_EMPTY_PARENTS_REFLOG.
 */
static void try_remove_empty_parents(struct files_ref_store *refs,
				     const char *refname,
				     unsigned int flags)
{
	struct strbuf buf = STRBUF_INIT;
	struct strbuf sb = STRBUF_INIT;
	char *p, *q;
	int i;

	strbuf_addstr(&buf, refname);
	p = buf.buf;
	for (i = 0; i < 2; i++) { /* refs/{heads,tags,...}/ */
		while (*p && *p != '/')
			p++;
		/* tolerate duplicate slashes; see check_refname_format() */
		while (*p == '/')
			p++;
	}
	q = buf.buf + buf.len;
	while (flags & (REMOVE_EMPTY_PARENTS_REF | REMOVE_EMPTY_PARENTS_REFLOG)) {
		while (q > p && *q != '/')
			q--;
		while (q > p && *(q-1) == '/')
			q--;
		if (q == p)
			break;
		strbuf_setlen(&buf, q - buf.buf);

		strbuf_reset(&sb);
		files_ref_path(refs, &sb, buf.buf);
		if ((flags & REMOVE_EMPTY_PARENTS_REF) && rmdir(sb.buf))
			flags &= ~REMOVE_EMPTY_PARENTS_REF;

		strbuf_reset(&sb);
		files_reflog_path(refs, &sb, buf.buf);
		if ((flags & REMOVE_EMPTY_PARENTS_REFLOG) && rmdir(sb.buf))
			flags &= ~REMOVE_EMPTY_PARENTS_REFLOG;
	}
	strbuf_release(&buf);
	strbuf_release(&sb);
}

/* make sure nobody touched the ref, and unlink */
static void prune_ref(struct files_ref_store *refs, struct ref_to_prune *r)
{
	struct ref_transaction *transaction;
	struct strbuf err = STRBUF_INIT;

	if (check_refname_format(r->name, 0))
		return;

	transaction = ref_store_transaction_begin(&refs->base, &err);
	if (!transaction ||
	    ref_transaction_delete(transaction, r->name, r->sha1,
				   REF_ISPRUNING | REF_NODEREF, NULL, &err) ||
	    ref_transaction_commit(transaction, &err)) {
		ref_transaction_free(transaction);
		error("%s", err.buf);
		strbuf_release(&err);
		return;
	}
	ref_transaction_free(transaction);
	strbuf_release(&err);
}

/*
 * Prune the loose versions of the references in the linked list
 * `*refs_to_prune`, freeing the entries in the list as we go.
 */
static void prune_refs(struct files_ref_store *refs, struct ref_to_prune **refs_to_prune)
{
	while (*refs_to_prune) {
		struct ref_to_prune *r = *refs_to_prune;
		*refs_to_prune = r->next;
		prune_ref(refs, r);
		free(r);
	}
}

/*
 * Return true if the specified reference should be packed.
 */
static int should_pack_ref(const char *refname,
			   const struct object_id *oid, unsigned int ref_flags,
			   unsigned int pack_flags)
{
	/* Do not pack per-worktree refs: */
	if (ref_type(refname) != REF_TYPE_NORMAL)
		return 0;

	/* Do not pack non-tags unless PACK_REFS_ALL is set: */
	if (!(pack_flags & PACK_REFS_ALL) && !starts_with(refname, "refs/tags/"))
		return 0;

	/* Do not pack symbolic refs: */
	if (ref_flags & REF_ISSYMREF)
		return 0;

	/* Do not pack broken refs: */
	if (!ref_resolves_to_object(refname, oid, ref_flags))
		return 0;

	return 1;
}

static int files_pack_refs(struct ref_store *ref_store, unsigned int flags)
{
	struct files_ref_store *refs =
		files_downcast(ref_store, REF_STORE_WRITE | REF_STORE_ODB,
			       "pack_refs");
	struct ref_iterator *iter;
	int ok;
	struct ref_to_prune *refs_to_prune = NULL;
	struct strbuf err = STRBUF_INIT;
	struct ref_transaction *transaction;

	transaction = ref_store_transaction_begin(refs->packed_ref_store, &err);
	if (!transaction)
		return -1;

	packed_refs_lock(refs->packed_ref_store, LOCK_DIE_ON_ERROR, &err);

	iter = cache_ref_iterator_begin(get_loose_ref_cache(refs), NULL, 0);
	while ((ok = ref_iterator_advance(iter)) == ITER_OK) {
		/*
		 * If the loose reference can be packed, add an entry
		 * in the packed ref cache. If the reference should be
		 * pruned, also add it to refs_to_prune.
		 */
		if (!should_pack_ref(iter->refname, iter->oid, iter->flags,
				     flags))
			continue;

		/*
		 * Add a reference creation for this reference to the
		 * packed-refs transaction:
		 */
		if (ref_transaction_update(transaction, iter->refname,
					   iter->oid->hash, NULL,
					   REF_NODEREF, NULL, &err))
			die("failure preparing to create packed reference %s: %s",
			    iter->refname, err.buf);

		/* Schedule the loose reference for pruning if requested. */
		if ((flags & PACK_REFS_PRUNE)) {
			struct ref_to_prune *n;
			FLEX_ALLOC_STR(n, name, iter->refname);
			hashcpy(n->sha1, iter->oid->hash);
			n->next = refs_to_prune;
			refs_to_prune = n;
		}
	}
	if (ok != ITER_DONE)
		die("error while iterating over references");

	if (ref_transaction_commit(transaction, &err))
		die("unable to write new packed-refs: %s", err.buf);

	ref_transaction_free(transaction);

	packed_refs_unlock(refs->packed_ref_store);

	prune_refs(refs, &refs_to_prune);
	strbuf_release(&err);
	return 0;
}

static int files_delete_refs(struct ref_store *ref_store, const char *msg,
			     struct string_list *refnames, unsigned int flags)
{
	struct files_ref_store *refs =
		files_downcast(ref_store, REF_STORE_WRITE, "delete_refs");
	struct strbuf err = STRBUF_INIT;
	int i, result = 0;

	if (!refnames->nr)
		return 0;

	if (packed_refs_lock(refs->packed_ref_store, 0, &err))
		goto error;

	if (refs_delete_refs(refs->packed_ref_store, msg, refnames, flags)) {
		packed_refs_unlock(refs->packed_ref_store);
		goto error;
	}

	packed_refs_unlock(refs->packed_ref_store);

	for (i = 0; i < refnames->nr; i++) {
		const char *refname = refnames->items[i].string;

		if (refs_delete_ref(&refs->base, msg, refname, NULL, flags))
			result |= error(_("could not remove reference %s"), refname);
	}

	strbuf_release(&err);
	return result;

error:
	/*
	 * If we failed to rewrite the packed-refs file, then it is
	 * unsafe to try to remove loose refs, because doing so might
	 * expose an obsolete packed value for a reference that might
	 * even point at an object that has been garbage collected.
	 */
	if (refnames->nr == 1)
		error(_("could not delete reference %s: %s"),
		      refnames->items[0].string, err.buf);
	else
		error(_("could not delete references: %s"), err.buf);

	strbuf_release(&err);
	return -1;
}

/*
 * People using contrib's git-new-workdir have .git/logs/refs ->
 * /some/other/path/.git/logs/refs, and that may live on another device.
 *
 * IOW, to avoid cross device rename errors, the temporary renamed log must
 * live into logs/refs.
 */
#define TMP_RENAMED_LOG  "refs/.tmp-renamed-log"

struct rename_cb {
	const char *tmp_renamed_log;
	int true_errno;
};

static int rename_tmp_log_callback(const char *path, void *cb_data)
{
	struct rename_cb *cb = cb_data;

	if (rename(cb->tmp_renamed_log, path)) {
		/*
		 * rename(a, b) when b is an existing directory ought
		 * to result in ISDIR, but Solaris 5.8 gives ENOTDIR.
		 * Sheesh. Record the true errno for error reporting,
		 * but report EISDIR to raceproof_create_file() so
		 * that it knows to retry.
		 */
		cb->true_errno = errno;
		if (errno == ENOTDIR)
			errno = EISDIR;
		return -1;
	} else {
		return 0;
	}
}

static int rename_tmp_log(struct files_ref_store *refs, const char *newrefname)
{
	struct strbuf path = STRBUF_INIT;
	struct strbuf tmp = STRBUF_INIT;
	struct rename_cb cb;
	int ret;

	files_reflog_path(refs, &path, newrefname);
	files_reflog_path(refs, &tmp, TMP_RENAMED_LOG);
	cb.tmp_renamed_log = tmp.buf;
	ret = raceproof_create_file(path.buf, rename_tmp_log_callback, &cb);
	if (ret) {
		if (errno == EISDIR)
			error("directory not empty: %s", path.buf);
		else
			error("unable to move logfile %s to %s: %s",
			      tmp.buf, path.buf,
			      strerror(cb.true_errno));
	}

	strbuf_release(&path);
	strbuf_release(&tmp);
	return ret;
}

static int write_ref_to_lockfile(struct ref_lock *lock,
				 const struct object_id *oid, struct strbuf *err);
static int commit_ref_update(struct files_ref_store *refs,
			     struct ref_lock *lock,
			     const struct object_id *oid, const char *logmsg,
			     struct strbuf *err);

static int files_rename_ref(struct ref_store *ref_store,
			    const char *oldrefname, const char *newrefname,
			    const char *logmsg)
{
	struct files_ref_store *refs =
		files_downcast(ref_store, REF_STORE_WRITE, "rename_ref");
	struct object_id oid, orig_oid;
	int flag = 0, logmoved = 0;
	struct ref_lock *lock;
	struct stat loginfo;
	struct strbuf sb_oldref = STRBUF_INIT;
	struct strbuf sb_newref = STRBUF_INIT;
	struct strbuf tmp_renamed_log = STRBUF_INIT;
	int log, ret;
	struct strbuf err = STRBUF_INIT;

	files_reflog_path(refs, &sb_oldref, oldrefname);
	files_reflog_path(refs, &sb_newref, newrefname);
	files_reflog_path(refs, &tmp_renamed_log, TMP_RENAMED_LOG);

	log = !lstat(sb_oldref.buf, &loginfo);
	if (log && S_ISLNK(loginfo.st_mode)) {
		ret = error("reflog for %s is a symlink", oldrefname);
		goto out;
	}

	if (!refs_resolve_ref_unsafe(&refs->base, oldrefname,
				     RESOLVE_REF_READING | RESOLVE_REF_NO_RECURSE,
				orig_oid.hash, &flag)) {
		ret = error("refname %s not found", oldrefname);
		goto out;
	}

	if (flag & REF_ISSYMREF) {
		ret = error("refname %s is a symbolic ref, renaming it is not supported",
			    oldrefname);
		goto out;
	}
	if (!refs_rename_ref_available(&refs->base, oldrefname, newrefname)) {
		ret = 1;
		goto out;
	}

	if (log && rename(sb_oldref.buf, tmp_renamed_log.buf)) {
		ret = error("unable to move logfile logs/%s to logs/"TMP_RENAMED_LOG": %s",
			    oldrefname, strerror(errno));
		goto out;
	}

	if (refs_delete_ref(&refs->base, logmsg, oldrefname,
			    orig_oid.hash, REF_NODEREF)) {
		error("unable to delete old %s", oldrefname);
		goto rollback;
	}

	/*
	 * Since we are doing a shallow lookup, oid is not the
	 * correct value to pass to delete_ref as old_oid. But that
	 * doesn't matter, because an old_oid check wouldn't add to
	 * the safety anyway; we want to delete the reference whatever
	 * its current value.
	 */
	if (!refs_read_ref_full(&refs->base, newrefname,
				RESOLVE_REF_READING | RESOLVE_REF_NO_RECURSE,
				oid.hash, NULL) &&
	    refs_delete_ref(&refs->base, NULL, newrefname,
			    NULL, REF_NODEREF)) {
		if (errno == EISDIR) {
			struct strbuf path = STRBUF_INIT;
			int result;

			files_ref_path(refs, &path, newrefname);
			result = remove_empty_directories(&path);
			strbuf_release(&path);

			if (result) {
				error("Directory not empty: %s", newrefname);
				goto rollback;
			}
		} else {
			error("unable to delete existing %s", newrefname);
			goto rollback;
		}
	}

	if (log && rename_tmp_log(refs, newrefname))
		goto rollback;

	logmoved = log;

	lock = lock_ref_sha1_basic(refs, newrefname, NULL, NULL, NULL,
				   REF_NODEREF, NULL, &err);
	if (!lock) {
		error("unable to rename '%s' to '%s': %s", oldrefname, newrefname, err.buf);
		strbuf_release(&err);
		goto rollback;
	}
	oidcpy(&lock->old_oid, &orig_oid);

	if (write_ref_to_lockfile(lock, &orig_oid, &err) ||
	    commit_ref_update(refs, lock, &orig_oid, logmsg, &err)) {
		error("unable to write current sha1 into %s: %s", newrefname, err.buf);
		strbuf_release(&err);
		goto rollback;
	}

	ret = 0;
	goto out;

 rollback:
	lock = lock_ref_sha1_basic(refs, oldrefname, NULL, NULL, NULL,
				   REF_NODEREF, NULL, &err);
	if (!lock) {
		error("unable to lock %s for rollback: %s", oldrefname, err.buf);
		strbuf_release(&err);
		goto rollbacklog;
	}

	flag = log_all_ref_updates;
	log_all_ref_updates = LOG_REFS_NONE;
	if (write_ref_to_lockfile(lock, &orig_oid, &err) ||
	    commit_ref_update(refs, lock, &orig_oid, NULL, &err)) {
		error("unable to write current sha1 into %s: %s", oldrefname, err.buf);
		strbuf_release(&err);
	}
	log_all_ref_updates = flag;

 rollbacklog:
	if (logmoved && rename(sb_newref.buf, sb_oldref.buf))
		error("unable to restore logfile %s from %s: %s",
			oldrefname, newrefname, strerror(errno));
	if (!logmoved && log &&
	    rename(tmp_renamed_log.buf, sb_oldref.buf))
		error("unable to restore logfile %s from logs/"TMP_RENAMED_LOG": %s",
			oldrefname, strerror(errno));
	ret = 1;
 out:
	strbuf_release(&sb_newref);
	strbuf_release(&sb_oldref);
	strbuf_release(&tmp_renamed_log);

	return ret;
}

static int close_ref_gently(struct ref_lock *lock)
{
	if (close_lock_file_gently(&lock->lk))
		return -1;
	return 0;
}

static int commit_ref(struct ref_lock *lock)
{
	char *path = get_locked_file_path(&lock->lk);
	struct stat st;

	if (!lstat(path, &st) && S_ISDIR(st.st_mode)) {
		/*
		 * There is a directory at the path we want to rename
		 * the lockfile to. Hopefully it is empty; try to
		 * delete it.
		 */
		size_t len = strlen(path);
		struct strbuf sb_path = STRBUF_INIT;

		strbuf_attach(&sb_path, path, len, len);

		/*
		 * If this fails, commit_lock_file() will also fail
		 * and will report the problem.
		 */
		remove_empty_directories(&sb_path);
		strbuf_release(&sb_path);
	} else {
		free(path);
	}

	if (commit_lock_file(&lock->lk))
		return -1;
	return 0;
}

static int open_or_create_logfile(const char *path, void *cb)
{
	int *fd = cb;

	*fd = open(path, O_APPEND | O_WRONLY | O_CREAT, 0666);
	return (*fd < 0) ? -1 : 0;
}

/*
 * Create a reflog for a ref. If force_create = 0, only create the
 * reflog for certain refs (those for which should_autocreate_reflog
 * returns non-zero). Otherwise, create it regardless of the reference
 * name. If the logfile already existed or was created, return 0 and
 * set *logfd to the file descriptor opened for appending to the file.
 * If no logfile exists and we decided not to create one, return 0 and
 * set *logfd to -1. On failure, fill in *err, set *logfd to -1, and
 * return -1.
 */
static int log_ref_setup(struct files_ref_store *refs,
			 const char *refname, int force_create,
			 int *logfd, struct strbuf *err)
{
	struct strbuf logfile_sb = STRBUF_INIT;
	char *logfile;

	files_reflog_path(refs, &logfile_sb, refname);
	logfile = strbuf_detach(&logfile_sb, NULL);

	if (force_create || should_autocreate_reflog(refname)) {
		if (raceproof_create_file(logfile, open_or_create_logfile, logfd)) {
			if (errno == ENOENT)
				strbuf_addf(err, "unable to create directory for '%s': "
					    "%s", logfile, strerror(errno));
			else if (errno == EISDIR)
				strbuf_addf(err, "there are still logs under '%s'",
					    logfile);
			else
				strbuf_addf(err, "unable to append to '%s': %s",
					    logfile, strerror(errno));

			goto error;
		}
	} else {
		*logfd = open(logfile, O_APPEND | O_WRONLY, 0666);
		if (*logfd < 0) {
			if (errno == ENOENT || errno == EISDIR) {
				/*
				 * The logfile doesn't already exist,
				 * but that is not an error; it only
				 * means that we won't write log
				 * entries to it.
				 */
				;
			} else {
				strbuf_addf(err, "unable to append to '%s': %s",
					    logfile, strerror(errno));
				goto error;
			}
		}
	}

	if (*logfd >= 0)
		adjust_shared_perm(logfile);

	free(logfile);
	return 0;

error:
	free(logfile);
	return -1;
}

static int files_create_reflog(struct ref_store *ref_store,
			       const char *refname, int force_create,
			       struct strbuf *err)
{
	struct files_ref_store *refs =
		files_downcast(ref_store, REF_STORE_WRITE, "create_reflog");
	int fd;

	if (log_ref_setup(refs, refname, force_create, &fd, err))
		return -1;

	if (fd >= 0)
		close(fd);

	return 0;
}

static int log_ref_write_fd(int fd, const struct object_id *old_oid,
			    const struct object_id *new_oid,
			    const char *committer, const char *msg)
{
	int msglen, written;
	unsigned maxlen, len;
	char *logrec;

	msglen = msg ? strlen(msg) : 0;
	maxlen = strlen(committer) + msglen + 100;
	logrec = xmalloc(maxlen);
	len = xsnprintf(logrec, maxlen, "%s %s %s\n",
			oid_to_hex(old_oid),
			oid_to_hex(new_oid),
			committer);
	if (msglen)
		len += copy_reflog_msg(logrec + len - 1, msg) - 1;

	written = len <= maxlen ? write_in_full(fd, logrec, len) : -1;
	free(logrec);
	if (written < 0)
		return -1;

	return 0;
}

static int files_log_ref_write(struct files_ref_store *refs,
			       const char *refname, const struct object_id *old_oid,
			       const struct object_id *new_oid, const char *msg,
			       int flags, struct strbuf *err)
{
	int logfd, result;

	if (log_all_ref_updates == LOG_REFS_UNSET)
		log_all_ref_updates = is_bare_repository() ? LOG_REFS_NONE : LOG_REFS_NORMAL;

	result = log_ref_setup(refs, refname,
			       flags & REF_FORCE_CREATE_REFLOG,
			       &logfd, err);

	if (result)
		return result;

	if (logfd < 0)
		return 0;
	result = log_ref_write_fd(logfd, old_oid, new_oid,
				  git_committer_info(0), msg);
	if (result) {
		struct strbuf sb = STRBUF_INIT;
		int save_errno = errno;

		files_reflog_path(refs, &sb, refname);
		strbuf_addf(err, "unable to append to '%s': %s",
			    sb.buf, strerror(save_errno));
		strbuf_release(&sb);
		close(logfd);
		return -1;
	}
	if (close(logfd)) {
		struct strbuf sb = STRBUF_INIT;
		int save_errno = errno;

		files_reflog_path(refs, &sb, refname);
		strbuf_addf(err, "unable to append to '%s': %s",
			    sb.buf, strerror(save_errno));
		strbuf_release(&sb);
		return -1;
	}
	return 0;
}

/*
 * Write sha1 into the open lockfile, then close the lockfile. On
 * errors, rollback the lockfile, fill in *err and
 * return -1.
 */
static int write_ref_to_lockfile(struct ref_lock *lock,
				 const struct object_id *oid, struct strbuf *err)
{
	static char term = '\n';
	struct object *o;
	int fd;

	o = parse_object(oid);
	if (!o) {
		strbuf_addf(err,
			    "trying to write ref '%s' with nonexistent object %s",
			    lock->ref_name, oid_to_hex(oid));
		unlock_ref(lock);
		return -1;
	}
	if (o->type != OBJ_COMMIT && is_branch(lock->ref_name)) {
		strbuf_addf(err,
			    "trying to write non-commit object %s to branch '%s'",
			    oid_to_hex(oid), lock->ref_name);
		unlock_ref(lock);
		return -1;
	}
	fd = get_lock_file_fd(&lock->lk);
	if (write_in_full(fd, oid_to_hex(oid), GIT_SHA1_HEXSZ) < 0 ||
	    write_in_full(fd, &term, 1) < 0 ||
	    close_ref_gently(lock) < 0) {
		strbuf_addf(err,
			    "couldn't write '%s'", get_lock_file_path(&lock->lk));
		unlock_ref(lock);
		return -1;
	}
	return 0;
}

/*
 * Commit a change to a loose reference that has already been written
 * to the loose reference lockfile. Also update the reflogs if
 * necessary, using the specified lockmsg (which can be NULL).
 */
static int commit_ref_update(struct files_ref_store *refs,
			     struct ref_lock *lock,
			     const struct object_id *oid, const char *logmsg,
			     struct strbuf *err)
{
	files_assert_main_repository(refs, "commit_ref_update");

	clear_loose_ref_cache(refs);
	if (files_log_ref_write(refs, lock->ref_name,
				&lock->old_oid, oid,
				logmsg, 0, err)) {
		char *old_msg = strbuf_detach(err, NULL);
		strbuf_addf(err, "cannot update the ref '%s': %s",
			    lock->ref_name, old_msg);
		free(old_msg);
		unlock_ref(lock);
		return -1;
	}

	if (strcmp(lock->ref_name, "HEAD") != 0) {
		/*
		 * Special hack: If a branch is updated directly and HEAD
		 * points to it (may happen on the remote side of a push
		 * for example) then logically the HEAD reflog should be
		 * updated too.
		 * A generic solution implies reverse symref information,
		 * but finding all symrefs pointing to the given branch
		 * would be rather costly for this rare event (the direct
		 * update of a branch) to be worth it.  So let's cheat and
		 * check with HEAD only which should cover 99% of all usage
		 * scenarios (even 100% of the default ones).
		 */
		int head_flag;
		const char *head_ref;

		head_ref = refs_resolve_ref_unsafe(&refs->base, "HEAD",
						   RESOLVE_REF_READING,
						   NULL, &head_flag);
		if (head_ref && (head_flag & REF_ISSYMREF) &&
		    !strcmp(head_ref, lock->ref_name)) {
			struct strbuf log_err = STRBUF_INIT;
			if (files_log_ref_write(refs, "HEAD",
						&lock->old_oid, oid,
						logmsg, 0, &log_err)) {
				error("%s", log_err.buf);
				strbuf_release(&log_err);
			}
		}
	}

	if (commit_ref(lock)) {
		strbuf_addf(err, "couldn't set '%s'", lock->ref_name);
		unlock_ref(lock);
		return -1;
	}

	unlock_ref(lock);
	return 0;
}

static int create_ref_symlink(struct ref_lock *lock, const char *target)
{
	int ret = -1;
#ifndef NO_SYMLINK_HEAD
	char *ref_path = get_locked_file_path(&lock->lk);
	unlink(ref_path);
	ret = symlink(target, ref_path);
	free(ref_path);

	if (ret)
		fprintf(stderr, "no symlink - falling back to symbolic ref\n");
#endif
	return ret;
}

static void update_symref_reflog(struct files_ref_store *refs,
				 struct ref_lock *lock, const char *refname,
				 const char *target, const char *logmsg)
{
	struct strbuf err = STRBUF_INIT;
	struct object_id new_oid;
	if (logmsg &&
	    !refs_read_ref_full(&refs->base, target,
				RESOLVE_REF_READING, new_oid.hash, NULL) &&
	    files_log_ref_write(refs, refname, &lock->old_oid,
				&new_oid, logmsg, 0, &err)) {
		error("%s", err.buf);
		strbuf_release(&err);
	}
}

static int create_symref_locked(struct files_ref_store *refs,
				struct ref_lock *lock, const char *refname,
				const char *target, const char *logmsg)
{
	if (prefer_symlink_refs && !create_ref_symlink(lock, target)) {
		update_symref_reflog(refs, lock, refname, target, logmsg);
		return 0;
	}

	if (!fdopen_lock_file(&lock->lk, "w"))
		return error("unable to fdopen %s: %s",
			     lock->lk.tempfile->filename.buf, strerror(errno));

	update_symref_reflog(refs, lock, refname, target, logmsg);

	/* no error check; commit_ref will check ferror */
	fprintf(lock->lk.tempfile->fp, "ref: %s\n", target);
	if (commit_ref(lock) < 0)
		return error("unable to write symref for %s: %s", refname,
			     strerror(errno));
	return 0;
}

static int files_create_symref(struct ref_store *ref_store,
			       const char *refname, const char *target,
			       const char *logmsg)
{
	struct files_ref_store *refs =
		files_downcast(ref_store, REF_STORE_WRITE, "create_symref");
	struct strbuf err = STRBUF_INIT;
	struct ref_lock *lock;
	int ret;

	lock = lock_ref_sha1_basic(refs, refname, NULL,
				   NULL, NULL, REF_NODEREF, NULL,
				   &err);
	if (!lock) {
		error("%s", err.buf);
		strbuf_release(&err);
		return -1;
	}

	ret = create_symref_locked(refs, lock, refname, target, logmsg);
	unlock_ref(lock);
	return ret;
}

static int files_reflog_exists(struct ref_store *ref_store,
			       const char *refname)
{
	struct files_ref_store *refs =
		files_downcast(ref_store, REF_STORE_READ, "reflog_exists");
	struct strbuf sb = STRBUF_INIT;
	struct stat st;
	int ret;

	files_reflog_path(refs, &sb, refname);
	ret = !lstat(sb.buf, &st) && S_ISREG(st.st_mode);
	strbuf_release(&sb);
	return ret;
}

static int files_delete_reflog(struct ref_store *ref_store,
			       const char *refname)
{
	struct files_ref_store *refs =
		files_downcast(ref_store, REF_STORE_WRITE, "delete_reflog");
	struct strbuf sb = STRBUF_INIT;
	int ret;

	files_reflog_path(refs, &sb, refname);
	ret = remove_path(sb.buf);
	strbuf_release(&sb);
	return ret;
}

static int show_one_reflog_ent(struct strbuf *sb, each_reflog_ent_fn fn, void *cb_data)
{
	struct object_id ooid, noid;
	char *email_end, *message;
	timestamp_t timestamp;
	int tz;
	const char *p = sb->buf;

	/* old SP new SP name <email> SP time TAB msg LF */
	if (!sb->len || sb->buf[sb->len - 1] != '\n' ||
	    parse_oid_hex(p, &ooid, &p) || *p++ != ' ' ||
	    parse_oid_hex(p, &noid, &p) || *p++ != ' ' ||
	    !(email_end = strchr(p, '>')) ||
	    email_end[1] != ' ' ||
	    !(timestamp = parse_timestamp(email_end + 2, &message, 10)) ||
	    !message || message[0] != ' ' ||
	    (message[1] != '+' && message[1] != '-') ||
	    !isdigit(message[2]) || !isdigit(message[3]) ||
	    !isdigit(message[4]) || !isdigit(message[5]))
		return 0; /* corrupt? */
	email_end[1] = '\0';
	tz = strtol(message + 1, NULL, 10);
	if (message[6] != '\t')
		message += 6;
	else
		message += 7;
	return fn(&ooid, &noid, p, timestamp, tz, message, cb_data);
}

static char *find_beginning_of_line(char *bob, char *scan)
{
	while (bob < scan && *(--scan) != '\n')
		; /* keep scanning backwards */
	/*
	 * Return either beginning of the buffer, or LF at the end of
	 * the previous line.
	 */
	return scan;
}

static int files_for_each_reflog_ent_reverse(struct ref_store *ref_store,
					     const char *refname,
					     each_reflog_ent_fn fn,
					     void *cb_data)
{
	struct files_ref_store *refs =
		files_downcast(ref_store, REF_STORE_READ,
			       "for_each_reflog_ent_reverse");
	struct strbuf sb = STRBUF_INIT;
	FILE *logfp;
	long pos;
	int ret = 0, at_tail = 1;

	files_reflog_path(refs, &sb, refname);
	logfp = fopen(sb.buf, "r");
	strbuf_release(&sb);
	if (!logfp)
		return -1;

	/* Jump to the end */
	if (fseek(logfp, 0, SEEK_END) < 0)
		ret = error("cannot seek back reflog for %s: %s",
			    refname, strerror(errno));
	pos = ftell(logfp);
	while (!ret && 0 < pos) {
		int cnt;
		size_t nread;
		char buf[BUFSIZ];
		char *endp, *scanp;

		/* Fill next block from the end */
		cnt = (sizeof(buf) < pos) ? sizeof(buf) : pos;
		if (fseek(logfp, pos - cnt, SEEK_SET)) {
			ret = error("cannot seek back reflog for %s: %s",
				    refname, strerror(errno));
			break;
		}
		nread = fread(buf, cnt, 1, logfp);
		if (nread != 1) {
			ret = error("cannot read %d bytes from reflog for %s: %s",
				    cnt, refname, strerror(errno));
			break;
		}
		pos -= cnt;

		scanp = endp = buf + cnt;
		if (at_tail && scanp[-1] == '\n')
			/* Looking at the final LF at the end of the file */
			scanp--;
		at_tail = 0;

		while (buf < scanp) {
			/*
			 * terminating LF of the previous line, or the beginning
			 * of the buffer.
			 */
			char *bp;

			bp = find_beginning_of_line(buf, scanp);

			if (*bp == '\n') {
				/*
				 * The newline is the end of the previous line,
				 * so we know we have complete line starting
				 * at (bp + 1). Prefix it onto any prior data
				 * we collected for the line and process it.
				 */
				strbuf_splice(&sb, 0, 0, bp + 1, endp - (bp + 1));
				scanp = bp;
				endp = bp + 1;
				ret = show_one_reflog_ent(&sb, fn, cb_data);
				strbuf_reset(&sb);
				if (ret)
					break;
			} else if (!pos) {
				/*
				 * We are at the start of the buffer, and the
				 * start of the file; there is no previous
				 * line, and we have everything for this one.
				 * Process it, and we can end the loop.
				 */
				strbuf_splice(&sb, 0, 0, buf, endp - buf);
				ret = show_one_reflog_ent(&sb, fn, cb_data);
				strbuf_reset(&sb);
				break;
			}

			if (bp == buf) {
				/*
				 * We are at the start of the buffer, and there
				 * is more file to read backwards. Which means
				 * we are in the middle of a line. Note that we
				 * may get here even if *bp was a newline; that
				 * just means we are at the exact end of the
				 * previous line, rather than some spot in the
				 * middle.
				 *
				 * Save away what we have to be combined with
				 * the data from the next read.
				 */
				strbuf_splice(&sb, 0, 0, buf, endp - buf);
				break;
			}
		}

	}
	if (!ret && sb.len)
		die("BUG: reverse reflog parser had leftover data");

	fclose(logfp);
	strbuf_release(&sb);
	return ret;
}

static int files_for_each_reflog_ent(struct ref_store *ref_store,
				     const char *refname,
				     each_reflog_ent_fn fn, void *cb_data)
{
	struct files_ref_store *refs =
		files_downcast(ref_store, REF_STORE_READ,
			       "for_each_reflog_ent");
	FILE *logfp;
	struct strbuf sb = STRBUF_INIT;
	int ret = 0;

	files_reflog_path(refs, &sb, refname);
	logfp = fopen(sb.buf, "r");
	strbuf_release(&sb);
	if (!logfp)
		return -1;

	while (!ret && !strbuf_getwholeline(&sb, logfp, '\n'))
		ret = show_one_reflog_ent(&sb, fn, cb_data);
	fclose(logfp);
	strbuf_release(&sb);
	return ret;
}

struct files_reflog_iterator {
	struct ref_iterator base;

	struct ref_store *ref_store;
	struct dir_iterator *dir_iterator;
	struct object_id oid;
};

static int files_reflog_iterator_advance(struct ref_iterator *ref_iterator)
{
	struct files_reflog_iterator *iter =
		(struct files_reflog_iterator *)ref_iterator;
	struct dir_iterator *diter = iter->dir_iterator;
	int ok;

	while ((ok = dir_iterator_advance(diter)) == ITER_OK) {
		int flags;

		if (!S_ISREG(diter->st.st_mode))
			continue;
		if (diter->basename[0] == '.')
			continue;
		if (ends_with(diter->basename, ".lock"))
			continue;

		if (refs_read_ref_full(iter->ref_store,
				       diter->relative_path, 0,
				       iter->oid.hash, &flags)) {
			error("bad ref for %s", diter->path.buf);
			continue;
		}

		iter->base.refname = diter->relative_path;
		iter->base.oid = &iter->oid;
		iter->base.flags = flags;
		return ITER_OK;
	}

	iter->dir_iterator = NULL;
	if (ref_iterator_abort(ref_iterator) == ITER_ERROR)
		ok = ITER_ERROR;
	return ok;
}

static int files_reflog_iterator_peel(struct ref_iterator *ref_iterator,
				   struct object_id *peeled)
{
	die("BUG: ref_iterator_peel() called for reflog_iterator");
}

static int files_reflog_iterator_abort(struct ref_iterator *ref_iterator)
{
	struct files_reflog_iterator *iter =
		(struct files_reflog_iterator *)ref_iterator;
	int ok = ITER_DONE;

	if (iter->dir_iterator)
		ok = dir_iterator_abort(iter->dir_iterator);

	base_ref_iterator_free(ref_iterator);
	return ok;
}

static struct ref_iterator_vtable files_reflog_iterator_vtable = {
	files_reflog_iterator_advance,
	files_reflog_iterator_peel,
	files_reflog_iterator_abort
};

static struct ref_iterator *reflog_iterator_begin(struct ref_store *ref_store,
						  const char *gitdir)
{
	struct files_reflog_iterator *iter = xcalloc(1, sizeof(*iter));
	struct ref_iterator *ref_iterator = &iter->base;
	struct strbuf sb = STRBUF_INIT;

	base_ref_iterator_init(ref_iterator, &files_reflog_iterator_vtable);
	strbuf_addf(&sb, "%s/logs", gitdir);
	iter->dir_iterator = dir_iterator_begin(sb.buf);
	iter->ref_store = ref_store;
	strbuf_release(&sb);

	return ref_iterator;
}

static enum iterator_selection reflog_iterator_select(
	struct ref_iterator *iter_worktree,
	struct ref_iterator *iter_common,
	void *cb_data)
{
	if (iter_worktree) {
		/*
		 * We're a bit loose here. We probably should ignore
		 * common refs if they are accidentally added as
		 * per-worktree refs.
		 */
		return ITER_SELECT_0;
	} else if (iter_common) {
		if (ref_type(iter_common->refname) == REF_TYPE_NORMAL)
			return ITER_SELECT_1;

		/*
		 * The main ref store may contain main worktree's
		 * per-worktree refs, which should be ignored
		 */
		return ITER_SKIP_1;
	} else
		return ITER_DONE;
}

static struct ref_iterator *files_reflog_iterator_begin(struct ref_store *ref_store)
{
	struct files_ref_store *refs =
		files_downcast(ref_store, REF_STORE_READ,
			       "reflog_iterator_begin");

	if (!strcmp(refs->gitdir, refs->gitcommondir)) {
		return reflog_iterator_begin(ref_store, refs->gitcommondir);
	} else {
		return merge_ref_iterator_begin(
			reflog_iterator_begin(ref_store, refs->gitdir),
			reflog_iterator_begin(ref_store, refs->gitcommondir),
			reflog_iterator_select, refs);
	}
}

/*
 * If update is a direct update of head_ref (the reference pointed to
 * by HEAD), then add an extra REF_LOG_ONLY update for HEAD.
 */
static int split_head_update(struct ref_update *update,
			     struct ref_transaction *transaction,
			     const char *head_ref,
			     struct string_list *affected_refnames,
			     struct strbuf *err)
{
	struct string_list_item *item;
	struct ref_update *new_update;

	if ((update->flags & REF_LOG_ONLY) ||
	    (update->flags & REF_ISPRUNING) ||
	    (update->flags & REF_UPDATE_VIA_HEAD))
		return 0;

	if (strcmp(update->refname, head_ref))
		return 0;

	/*
	 * First make sure that HEAD is not already in the
	 * transaction. This check is O(lg N) in the transaction
	 * size, but it happens at most once per transaction.
	 */
	if (string_list_has_string(affected_refnames, "HEAD")) {
		/* An entry already existed */
		strbuf_addf(err,
			    "multiple updates for 'HEAD' (including one "
			    "via its referent '%s') are not allowed",
			    update->refname);
		return TRANSACTION_NAME_CONFLICT;
	}

	new_update = ref_transaction_add_update(
			transaction, "HEAD",
			update->flags | REF_LOG_ONLY | REF_NODEREF,
			update->new_oid.hash, update->old_oid.hash,
			update->msg);

	/*
	 * Add "HEAD". This insertion is O(N) in the transaction
	 * size, but it happens at most once per transaction.
	 * Add new_update->refname instead of a literal "HEAD".
	 */
	if (strcmp(new_update->refname, "HEAD"))
		BUG("%s unexpectedly not 'HEAD'", new_update->refname);
	item = string_list_insert(affected_refnames, new_update->refname);
	item->util = new_update;

	return 0;
}

/*
 * update is for a symref that points at referent and doesn't have
 * REF_NODEREF set. Split it into two updates:
 * - The original update, but with REF_LOG_ONLY and REF_NODEREF set
 * - A new, separate update for the referent reference
 * Note that the new update will itself be subject to splitting when
 * the iteration gets to it.
 */
static int split_symref_update(struct files_ref_store *refs,
			       struct ref_update *update,
			       const char *referent,
			       struct ref_transaction *transaction,
			       struct string_list *affected_refnames,
			       struct strbuf *err)
{
	struct string_list_item *item;
	struct ref_update *new_update;
	unsigned int new_flags;

	/*
	 * First make sure that referent is not already in the
	 * transaction. This check is O(lg N) in the transaction
	 * size, but it happens at most once per symref in a
	 * transaction.
	 */
	if (string_list_has_string(affected_refnames, referent)) {
		/* An entry already exists */
		strbuf_addf(err,
			    "multiple updates for '%s' (including one "
			    "via symref '%s') are not allowed",
			    referent, update->refname);
		return TRANSACTION_NAME_CONFLICT;
	}

	new_flags = update->flags;
	if (!strcmp(update->refname, "HEAD")) {
		/*
		 * Record that the new update came via HEAD, so that
		 * when we process it, split_head_update() doesn't try
		 * to add another reflog update for HEAD. Note that
		 * this bit will be propagated if the new_update
		 * itself needs to be split.
		 */
		new_flags |= REF_UPDATE_VIA_HEAD;
	}

	new_update = ref_transaction_add_update(
			transaction, referent, new_flags,
			update->new_oid.hash, update->old_oid.hash,
			update->msg);

	new_update->parent_update = update;

	/*
	 * Change the symbolic ref update to log only. Also, it
	 * doesn't need to check its old SHA-1 value, as that will be
	 * done when new_update is processed.
	 */
	update->flags |= REF_LOG_ONLY | REF_NODEREF;
	update->flags &= ~REF_HAVE_OLD;

	/*
	 * Add the referent. This insertion is O(N) in the transaction
	 * size, but it happens at most once per symref in a
	 * transaction. Make sure to add new_update->refname, which will
	 * be valid as long as affected_refnames is in use, and NOT
	 * referent, which might soon be freed by our caller.
	 */
	item = string_list_insert(affected_refnames, new_update->refname);
	if (item->util)
		BUG("%s unexpectedly found in affected_refnames",
		    new_update->refname);
	item->util = new_update;

	return 0;
}

/*
 * Return the refname under which update was originally requested.
 */
static const char *original_update_refname(struct ref_update *update)
{
	while (update->parent_update)
		update = update->parent_update;

	return update->refname;
}

/*
 * Check whether the REF_HAVE_OLD and old_oid values stored in update
 * are consistent with oid, which is the reference's current value. If
 * everything is OK, return 0; otherwise, write an error message to
 * err and return -1.
 */
static int check_old_oid(struct ref_update *update, struct object_id *oid,
			 struct strbuf *err)
{
	if (!(update->flags & REF_HAVE_OLD) ||
		   !oidcmp(oid, &update->old_oid))
		return 0;

	if (is_null_oid(&update->old_oid))
		strbuf_addf(err, "cannot lock ref '%s': "
			    "reference already exists",
			    original_update_refname(update));
	else if (is_null_oid(oid))
		strbuf_addf(err, "cannot lock ref '%s': "
			    "reference is missing but expected %s",
			    original_update_refname(update),
			    oid_to_hex(&update->old_oid));
	else
		strbuf_addf(err, "cannot lock ref '%s': "
			    "is at %s but expected %s",
			    original_update_refname(update),
			    oid_to_hex(oid),
			    oid_to_hex(&update->old_oid));

	return -1;
}

/*
 * Prepare for carrying out update:
 * - Lock the reference referred to by update.
 * - Read the reference under lock.
 * - Check that its old SHA-1 value (if specified) is correct, and in
 *   any case record it in update->lock->old_oid for later use when
 *   writing the reflog.
 * - If it is a symref update without REF_NODEREF, split it up into a
 *   REF_LOG_ONLY update of the symref and add a separate update for
 *   the referent to transaction.
 * - If it is an update of head_ref, add a corresponding REF_LOG_ONLY
 *   update of HEAD.
 */
static int lock_ref_for_update(struct files_ref_store *refs,
			       struct ref_update *update,
			       struct ref_transaction *transaction,
			       const char *head_ref,
			       struct string_list *affected_refnames,
			       struct strbuf *err)
{
	struct strbuf referent = STRBUF_INIT;
	int mustexist = (update->flags & REF_HAVE_OLD) &&
		!is_null_oid(&update->old_oid);
	int ret = 0;
	struct ref_lock *lock;

	files_assert_main_repository(refs, "lock_ref_for_update");

	if ((update->flags & REF_HAVE_NEW) && is_null_oid(&update->new_oid))
		update->flags |= REF_DELETING;

	if (head_ref) {
		ret = split_head_update(update, transaction, head_ref,
					affected_refnames, err);
		if (ret)
			goto out;
	}

	ret = lock_raw_ref(refs, update->refname, mustexist,
			   affected_refnames, NULL,
			   &lock, &referent,
			   &update->type, err);
	if (ret) {
		char *reason;

		reason = strbuf_detach(err, NULL);
		strbuf_addf(err, "cannot lock ref '%s': %s",
			    original_update_refname(update), reason);
		free(reason);
		goto out;
	}

	update->backend_data = lock;

	if (update->type & REF_ISSYMREF) {
		if (update->flags & REF_NODEREF) {
			/*
			 * We won't be reading the referent as part of
			 * the transaction, so we have to read it here
			 * to record and possibly check old_sha1:
			 */
			if (refs_read_ref_full(&refs->base,
					       referent.buf, 0,
					       lock->old_oid.hash, NULL)) {
				if (update->flags & REF_HAVE_OLD) {
					strbuf_addf(err, "cannot lock ref '%s': "
						    "error reading reference",
						    original_update_refname(update));
					ret = TRANSACTION_GENERIC_ERROR;
					goto out;
				}
			} else if (check_old_oid(update, &lock->old_oid, err)) {
				ret = TRANSACTION_GENERIC_ERROR;
				goto out;
			}
		} else {
			/*
			 * Create a new update for the reference this
			 * symref is pointing at. Also, we will record
			 * and verify old_sha1 for this update as part
			 * of processing the split-off update, so we
			 * don't have to do it here.
			 */
			ret = split_symref_update(refs, update,
						  referent.buf, transaction,
						  affected_refnames, err);
			if (ret)
				goto out;
		}
	} else {
		struct ref_update *parent_update;

		if (check_old_oid(update, &lock->old_oid, err)) {
			ret = TRANSACTION_GENERIC_ERROR;
			goto out;
		}

		/*
		 * If this update is happening indirectly because of a
		 * symref update, record the old SHA-1 in the parent
		 * update:
		 */
		for (parent_update = update->parent_update;
		     parent_update;
		     parent_update = parent_update->parent_update) {
			struct ref_lock *parent_lock = parent_update->backend_data;
			oidcpy(&parent_lock->old_oid, &lock->old_oid);
		}
	}

	if ((update->flags & REF_HAVE_NEW) &&
	    !(update->flags & REF_DELETING) &&
	    !(update->flags & REF_LOG_ONLY)) {
		if (!(update->type & REF_ISSYMREF) &&
		    !oidcmp(&lock->old_oid, &update->new_oid)) {
			/*
			 * The reference already has the desired
			 * value, so we don't need to write it.
			 */
		} else if (write_ref_to_lockfile(lock, &update->new_oid,
						 err)) {
			char *write_err = strbuf_detach(err, NULL);

			/*
			 * The lock was freed upon failure of
			 * write_ref_to_lockfile():
			 */
			update->backend_data = NULL;
			strbuf_addf(err,
				    "cannot update ref '%s': %s",
				    update->refname, write_err);
			free(write_err);
			ret = TRANSACTION_GENERIC_ERROR;
			goto out;
		} else {
			update->flags |= REF_NEEDS_COMMIT;
		}
	}
	if (!(update->flags & REF_NEEDS_COMMIT)) {
		/*
		 * We didn't call write_ref_to_lockfile(), so
		 * the lockfile is still open. Close it to
		 * free up the file descriptor:
		 */
		if (close_ref_gently(lock)) {
			strbuf_addf(err, "couldn't close '%s.lock'",
				    update->refname);
			ret = TRANSACTION_GENERIC_ERROR;
			goto out;
		}
	}

out:
	strbuf_release(&referent);
	return ret;
}

struct files_transaction_backend_data {
	struct ref_transaction *packed_transaction;
	int packed_refs_locked;
};

/*
 * Unlock any references in `transaction` that are still locked, and
 * mark the transaction closed.
 */
static void files_transaction_cleanup(struct files_ref_store *refs,
				      struct ref_transaction *transaction)
{
	size_t i;
	struct files_transaction_backend_data *backend_data =
		transaction->backend_data;
	struct strbuf err = STRBUF_INIT;

	for (i = 0; i < transaction->nr; i++) {
		struct ref_update *update = transaction->updates[i];
		struct ref_lock *lock = update->backend_data;

		if (lock) {
			unlock_ref(lock);
			update->backend_data = NULL;
		}
	}

	if (backend_data->packed_transaction &&
	    ref_transaction_abort(backend_data->packed_transaction, &err)) {
		error("error aborting transaction: %s", err.buf);
		strbuf_release(&err);
	}

	if (backend_data->packed_refs_locked)
		packed_refs_unlock(refs->packed_ref_store);

	free(backend_data);

	transaction->state = REF_TRANSACTION_CLOSED;
}

static int files_transaction_prepare(struct ref_store *ref_store,
				     struct ref_transaction *transaction,
				     struct strbuf *err)
{
	struct files_ref_store *refs =
		files_downcast(ref_store, REF_STORE_WRITE,
			       "ref_transaction_prepare");
	size_t i;
	int ret = 0;
	struct string_list affected_refnames = STRING_LIST_INIT_NODUP;
	char *head_ref = NULL;
	int head_type;
	struct object_id head_oid;
	struct files_transaction_backend_data *backend_data;
	struct ref_transaction *packed_transaction = NULL;

	assert(err);

	if (!transaction->nr)
		goto cleanup;

	backend_data = xcalloc(1, sizeof(*backend_data));
	transaction->backend_data = backend_data;

	/*
	 * Fail if a refname appears more than once in the
	 * transaction. (If we end up splitting up any updates using
	 * split_symref_update() or split_head_update(), those
	 * functions will check that the new updates don't have the
	 * same refname as any existing ones.)
	 */
	for (i = 0; i < transaction->nr; i++) {
		struct ref_update *update = transaction->updates[i];
		struct string_list_item *item =
			string_list_append(&affected_refnames, update->refname);

		/*
		 * We store a pointer to update in item->util, but at
		 * the moment we never use the value of this field
		 * except to check whether it is non-NULL.
		 */
		item->util = update;
	}
	string_list_sort(&affected_refnames);
	if (ref_update_reject_duplicates(&affected_refnames, err)) {
		ret = TRANSACTION_GENERIC_ERROR;
		goto cleanup;
	}

	/*
	 * Special hack: If a branch is updated directly and HEAD
	 * points to it (may happen on the remote side of a push
	 * for example) then logically the HEAD reflog should be
	 * updated too.
	 *
	 * A generic solution would require reverse symref lookups,
	 * but finding all symrefs pointing to a given branch would be
	 * rather costly for this rare event (the direct update of a
	 * branch) to be worth it. So let's cheat and check with HEAD
	 * only, which should cover 99% of all usage scenarios (even
	 * 100% of the default ones).
	 *
	 * So if HEAD is a symbolic reference, then record the name of
	 * the reference that it points to. If we see an update of
	 * head_ref within the transaction, then split_head_update()
	 * arranges for the reflog of HEAD to be updated, too.
	 */
	head_ref = refs_resolve_refdup(ref_store, "HEAD",
				       RESOLVE_REF_NO_RECURSE,
				       head_oid.hash, &head_type);

	if (head_ref && !(head_type & REF_ISSYMREF)) {
		FREE_AND_NULL(head_ref);
	}

	/*
	 * Acquire all locks, verify old values if provided, check
	 * that new values are valid, and write new values to the
	 * lockfiles, ready to be activated. Only keep one lockfile
	 * open at a time to avoid running out of file descriptors.
	 * Note that lock_ref_for_update() might append more updates
	 * to the transaction.
	 */
	for (i = 0; i < transaction->nr; i++) {
		struct ref_update *update = transaction->updates[i];

		ret = lock_ref_for_update(refs, update, transaction,
					  head_ref, &affected_refnames, err);
		if (ret)
			break;

		if (update->flags & REF_DELETING &&
		    !(update->flags & REF_LOG_ONLY) &&
		    !(update->flags & REF_ISPRUNING)) {
			/*
			 * This reference has to be deleted from
			 * packed-refs if it exists there.
			 */
			if (!packed_transaction) {
				packed_transaction = ref_store_transaction_begin(
						refs->packed_ref_store, err);
				if (!packed_transaction) {
					ret = TRANSACTION_GENERIC_ERROR;
					goto cleanup;
				}

				backend_data->packed_transaction =
					packed_transaction;
			}

			ref_transaction_add_update(
					packed_transaction, update->refname,
					update->flags & ~REF_HAVE_OLD,
					update->new_oid.hash, update->old_oid.hash,
					NULL);
		}
	}

	if (packed_transaction) {
		if (packed_refs_lock(refs->packed_ref_store, 0, err)) {
			ret = TRANSACTION_GENERIC_ERROR;
			goto cleanup;
		}
		backend_data->packed_refs_locked = 1;
		ret = ref_transaction_prepare(packed_transaction, err);
	}

cleanup:
	free(head_ref);
	string_list_clear(&affected_refnames, 0);

	if (ret)
		files_transaction_cleanup(refs, transaction);
	else
		transaction->state = REF_TRANSACTION_PREPARED;

	return ret;
}

static int files_transaction_finish(struct ref_store *ref_store,
				    struct ref_transaction *transaction,
				    struct strbuf *err)
{
	struct files_ref_store *refs =
		files_downcast(ref_store, 0, "ref_transaction_finish");
	size_t i;
	int ret = 0;
	struct strbuf sb = STRBUF_INIT;
	struct files_transaction_backend_data *backend_data;
	struct ref_transaction *packed_transaction;


	assert(err);

	if (!transaction->nr) {
		transaction->state = REF_TRANSACTION_CLOSED;
		return 0;
	}

	backend_data = transaction->backend_data;
	packed_transaction = backend_data->packed_transaction;

	/* Perform updates first so live commits remain referenced */
	for (i = 0; i < transaction->nr; i++) {
		struct ref_update *update = transaction->updates[i];
		struct ref_lock *lock = update->backend_data;

		if (update->flags & REF_NEEDS_COMMIT ||
		    update->flags & REF_LOG_ONLY) {
			if (files_log_ref_write(refs,
						lock->ref_name,
						&lock->old_oid,
						&update->new_oid,
						update->msg, update->flags,
						err)) {
				char *old_msg = strbuf_detach(err, NULL);

				strbuf_addf(err, "cannot update the ref '%s': %s",
					    lock->ref_name, old_msg);
				free(old_msg);
				unlock_ref(lock);
				update->backend_data = NULL;
				ret = TRANSACTION_GENERIC_ERROR;
				goto cleanup;
			}
		}
		if (update->flags & REF_NEEDS_COMMIT) {
			clear_loose_ref_cache(refs);
			if (commit_ref(lock)) {
				strbuf_addf(err, "couldn't set '%s'", lock->ref_name);
				unlock_ref(lock);
				update->backend_data = NULL;
				ret = TRANSACTION_GENERIC_ERROR;
				goto cleanup;
			}
		}
	}

	/*
	 * Now that updates are safely completed, we can perform
	 * deletes. First delete the reflogs of any references that
	 * will be deleted, since (in the unexpected event of an
	 * error) leaving a reference without a reflog is less bad
	 * than leaving a reflog without a reference (the latter is a
	 * mildly invalid repository state):
	 */
	for (i = 0; i < transaction->nr; i++) {
		struct ref_update *update = transaction->updates[i];
		if (update->flags & REF_DELETING &&
		    !(update->flags & REF_LOG_ONLY) &&
		    !(update->flags & REF_ISPRUNING)) {
			strbuf_reset(&sb);
			files_reflog_path(refs, &sb, update->refname);
			if (!unlink_or_warn(sb.buf))
				try_remove_empty_parents(refs, update->refname,
							 REMOVE_EMPTY_PARENTS_REFLOG);
		}
	}

	/*
	 * Perform deletes now that updates are safely completed.
	 *
	 * First delete any packed versions of the references, while
	 * retaining the packed-refs lock:
	 */
	if (packed_transaction) {
		ret = ref_transaction_commit(packed_transaction, err);
		ref_transaction_free(packed_transaction);
		packed_transaction = NULL;
		backend_data->packed_transaction = NULL;
		if (ret)
			goto cleanup;
	}

	/* Now delete the loose versions of the references: */
	for (i = 0; i < transaction->nr; i++) {
		struct ref_update *update = transaction->updates[i];
		struct ref_lock *lock = update->backend_data;

		if (update->flags & REF_DELETING &&
		    !(update->flags & REF_LOG_ONLY)) {
			if (!(update->type & REF_ISPACKED) ||
			    update->type & REF_ISSYMREF) {
				/* It is a loose reference. */
				strbuf_reset(&sb);
				files_ref_path(refs, &sb, lock->ref_name);
				if (unlink_or_msg(sb.buf, err)) {
					ret = TRANSACTION_GENERIC_ERROR;
					goto cleanup;
				}
				update->flags |= REF_DELETED_LOOSE;
			}
		}
	}

	clear_loose_ref_cache(refs);

cleanup:
	files_transaction_cleanup(refs, transaction);

	for (i = 0; i < transaction->nr; i++) {
		struct ref_update *update = transaction->updates[i];

		if (update->flags & REF_DELETED_LOOSE) {
			/*
			 * The loose reference was deleted. Delete any
			 * empty parent directories. (Note that this
			 * can only work because we have already
			 * removed the lockfile.)
			 */
			try_remove_empty_parents(refs, update->refname,
						 REMOVE_EMPTY_PARENTS_REF);
		}
	}

	strbuf_release(&sb);
	return ret;
}

static int files_transaction_abort(struct ref_store *ref_store,
				   struct ref_transaction *transaction,
				   struct strbuf *err)
{
	struct files_ref_store *refs =
		files_downcast(ref_store, 0, "ref_transaction_abort");

	files_transaction_cleanup(refs, transaction);
	return 0;
}

static int ref_present(const char *refname,
		       const struct object_id *oid, int flags, void *cb_data)
{
	struct string_list *affected_refnames = cb_data;

	return string_list_has_string(affected_refnames, refname);
}

static int files_initial_transaction_commit(struct ref_store *ref_store,
					    struct ref_transaction *transaction,
					    struct strbuf *err)
{
	struct files_ref_store *refs =
		files_downcast(ref_store, REF_STORE_WRITE,
			       "initial_ref_transaction_commit");
	size_t i;
	int ret = 0;
	struct string_list affected_refnames = STRING_LIST_INIT_NODUP;
	struct ref_transaction *packed_transaction = NULL;

	assert(err);

	if (transaction->state != REF_TRANSACTION_OPEN)
		die("BUG: commit called for transaction that is not open");

	/* Fail if a refname appears more than once in the transaction: */
	for (i = 0; i < transaction->nr; i++)
		string_list_append(&affected_refnames,
				   transaction->updates[i]->refname);
	string_list_sort(&affected_refnames);
	if (ref_update_reject_duplicates(&affected_refnames, err)) {
		ret = TRANSACTION_GENERIC_ERROR;
		goto cleanup;
	}

	/*
	 * It's really undefined to call this function in an active
	 * repository or when there are existing references: we are
	 * only locking and changing packed-refs, so (1) any
	 * simultaneous processes might try to change a reference at
	 * the same time we do, and (2) any existing loose versions of
	 * the references that we are setting would have precedence
	 * over our values. But some remote helpers create the remote
	 * "HEAD" and "master" branches before calling this function,
	 * so here we really only check that none of the references
	 * that we are creating already exists.
	 */
	if (refs_for_each_rawref(&refs->base, ref_present,
				 &affected_refnames))
		die("BUG: initial ref transaction called with existing refs");

	packed_transaction = ref_store_transaction_begin(refs->packed_ref_store, err);
	if (!packed_transaction) {
		ret = TRANSACTION_GENERIC_ERROR;
		goto cleanup;
	}

	for (i = 0; i < transaction->nr; i++) {
		struct ref_update *update = transaction->updates[i];

		if ((update->flags & REF_HAVE_OLD) &&
		    !is_null_oid(&update->old_oid))
			die("BUG: initial ref transaction with old_sha1 set");
		if (refs_verify_refname_available(&refs->base, update->refname,
						  &affected_refnames, NULL,
						  err)) {
			ret = TRANSACTION_NAME_CONFLICT;
			goto cleanup;
		}

		/*
		 * Add a reference creation for this reference to the
		 * packed-refs transaction:
		 */
		ref_transaction_add_update(packed_transaction, update->refname,
					   update->flags & ~REF_HAVE_OLD,
					   update->new_oid.hash, update->old_oid.hash,
					   NULL);
	}

	if (packed_refs_lock(refs->packed_ref_store, 0, err)) {
		ret = TRANSACTION_GENERIC_ERROR;
		goto cleanup;
	}

	if (initial_ref_transaction_commit(packed_transaction, err)) {
		ret = TRANSACTION_GENERIC_ERROR;
		goto cleanup;
	}

cleanup:
	if (packed_transaction)
		ref_transaction_free(packed_transaction);
	packed_refs_unlock(refs->packed_ref_store);
	transaction->state = REF_TRANSACTION_CLOSED;
	string_list_clear(&affected_refnames, 0);
	return ret;
}

struct expire_reflog_cb {
	unsigned int flags;
	reflog_expiry_should_prune_fn *should_prune_fn;
	void *policy_cb;
	FILE *newlog;
	struct object_id last_kept_oid;
};

static int expire_reflog_ent(struct object_id *ooid, struct object_id *noid,
			     const char *email, timestamp_t timestamp, int tz,
			     const char *message, void *cb_data)
{
	struct expire_reflog_cb *cb = cb_data;
	struct expire_reflog_policy_cb *policy_cb = cb->policy_cb;

	if (cb->flags & EXPIRE_REFLOGS_REWRITE)
		ooid = &cb->last_kept_oid;

	if ((*cb->should_prune_fn)(ooid, noid, email, timestamp, tz,
				   message, policy_cb)) {
		if (!cb->newlog)
			printf("would prune %s", message);
		else if (cb->flags & EXPIRE_REFLOGS_VERBOSE)
			printf("prune %s", message);
	} else {
		if (cb->newlog) {
			fprintf(cb->newlog, "%s %s %s %"PRItime" %+05d\t%s",
				oid_to_hex(ooid), oid_to_hex(noid),
				email, timestamp, tz, message);
			oidcpy(&cb->last_kept_oid, noid);
		}
		if (cb->flags & EXPIRE_REFLOGS_VERBOSE)
			printf("keep %s", message);
	}
	return 0;
}

static int files_reflog_expire(struct ref_store *ref_store,
			       const char *refname, const unsigned char *sha1,
			       unsigned int flags,
			       reflog_expiry_prepare_fn prepare_fn,
			       reflog_expiry_should_prune_fn should_prune_fn,
			       reflog_expiry_cleanup_fn cleanup_fn,
			       void *policy_cb_data)
{
	struct files_ref_store *refs =
		files_downcast(ref_store, REF_STORE_WRITE, "reflog_expire");
	static struct lock_file reflog_lock;
	struct expire_reflog_cb cb;
	struct ref_lock *lock;
	struct strbuf log_file_sb = STRBUF_INIT;
	char *log_file;
	int status = 0;
	int type;
	struct strbuf err = STRBUF_INIT;
	struct object_id oid;

	memset(&cb, 0, sizeof(cb));
	cb.flags = flags;
	cb.policy_cb = policy_cb_data;
	cb.should_prune_fn = should_prune_fn;

	/*
	 * The reflog file is locked by holding the lock on the
	 * reference itself, plus we might need to update the
	 * reference if --updateref was specified:
	 */
	lock = lock_ref_sha1_basic(refs, refname, sha1,
				   NULL, NULL, REF_NODEREF,
				   &type, &err);
	if (!lock) {
		error("cannot lock ref '%s': %s", refname, err.buf);
		strbuf_release(&err);
		return -1;
	}
	if (!refs_reflog_exists(ref_store, refname)) {
		unlock_ref(lock);
		return 0;
	}

	files_reflog_path(refs, &log_file_sb, refname);
	log_file = strbuf_detach(&log_file_sb, NULL);
	if (!(flags & EXPIRE_REFLOGS_DRY_RUN)) {
		/*
		 * Even though holding $GIT_DIR/logs/$reflog.lock has
		 * no locking implications, we use the lock_file
		 * machinery here anyway because it does a lot of the
		 * work we need, including cleaning up if the program
		 * exits unexpectedly.
		 */
		if (hold_lock_file_for_update(&reflog_lock, log_file, 0) < 0) {
			struct strbuf err = STRBUF_INIT;
			unable_to_lock_message(log_file, errno, &err);
			error("%s", err.buf);
			strbuf_release(&err);
			goto failure;
		}
		cb.newlog = fdopen_lock_file(&reflog_lock, "w");
		if (!cb.newlog) {
			error("cannot fdopen %s (%s)",
			      get_lock_file_path(&reflog_lock), strerror(errno));
			goto failure;
		}
	}

	hashcpy(oid.hash, sha1);

	(*prepare_fn)(refname, &oid, cb.policy_cb);
	refs_for_each_reflog_ent(ref_store, refname, expire_reflog_ent, &cb);
	(*cleanup_fn)(cb.policy_cb);

	if (!(flags & EXPIRE_REFLOGS_DRY_RUN)) {
		/*
		 * It doesn't make sense to adjust a reference pointed
		 * to by a symbolic ref based on expiring entries in
		 * the symbolic reference's reflog. Nor can we update
		 * a reference if there are no remaining reflog
		 * entries.
		 */
		int update = (flags & EXPIRE_REFLOGS_UPDATE_REF) &&
			!(type & REF_ISSYMREF) &&
			!is_null_oid(&cb.last_kept_oid);

		if (close_lock_file_gently(&reflog_lock)) {
			status |= error("couldn't write %s: %s", log_file,
					strerror(errno));
			rollback_lock_file(&reflog_lock);
		} else if (update &&
			   (write_in_full(get_lock_file_fd(&lock->lk),
				oid_to_hex(&cb.last_kept_oid), GIT_SHA1_HEXSZ) < 0 ||
			    write_str_in_full(get_lock_file_fd(&lock->lk), "\n") < 1 ||
			    close_ref_gently(lock) < 0)) {
			status |= error("couldn't write %s",
					get_lock_file_path(&lock->lk));
			rollback_lock_file(&reflog_lock);
		} else if (commit_lock_file(&reflog_lock)) {
			status |= error("unable to write reflog '%s' (%s)",
					log_file, strerror(errno));
		} else if (update && commit_ref(lock)) {
			status |= error("couldn't set %s", lock->ref_name);
		}
	}
	free(log_file);
	unlock_ref(lock);
	return status;

 failure:
	rollback_lock_file(&reflog_lock);
	free(log_file);
	unlock_ref(lock);
	return -1;
}

static int files_init_db(struct ref_store *ref_store, struct strbuf *err)
{
	struct files_ref_store *refs =
		files_downcast(ref_store, REF_STORE_WRITE, "init_db");
	struct strbuf sb = STRBUF_INIT;

	/*
	 * Create .git/refs/{heads,tags}
	 */
	files_ref_path(refs, &sb, "refs/heads");
	safe_create_dir(sb.buf, 1);

	strbuf_reset(&sb);
	files_ref_path(refs, &sb, "refs/tags");
	safe_create_dir(sb.buf, 1);

	strbuf_release(&sb);
	return 0;
}

struct ref_storage_be refs_be_files = {
	NULL,
	"files",
	files_ref_store_create,
	files_init_db,
	files_transaction_prepare,
	files_transaction_finish,
	files_transaction_abort,
	files_initial_transaction_commit,

	files_pack_refs,
	files_peel_ref,
	files_create_symref,
	files_delete_refs,
	files_rename_ref,

	files_ref_iterator_begin,
	files_read_raw_ref,

	files_reflog_iterator_begin,
	files_for_each_reflog_ent,
	files_for_each_reflog_ent_reverse,
	files_reflog_exists,
	files_create_reflog,
	files_delete_reflog,
	files_reflog_expire
};