com32/chain: allow service-only runs

This patch introduces small feature, allowing so called "service-only"
runs - where the chain modules does everything as instructed, but
otherwise doesn't perform actual chainloading.

This is useful for 'mbrchs', '[un]hide[all]' and 'setbpb'+'save'
options, making possible adjustments to partition/boot sector values on
any disk/partition.

See 'chain' option in doc/chain.txt for more details.

Signed-off-by: Michal Soltys <soltys@ziu.info>

3 files changed, 31 insertions, 13 deletions

diff --git a/com32/chain/chain.c b/com32/chain/chain.c
index 25d8fa75..73d107d8 100644
--- a/com32/chain/chain.c
+++ b/com32/chain/chain.c
@@ -662,9 +662,10 @@ int main(int argc, char *argv[])
     memset(&hdat, 0, sizeof(hdat));
     memset(&sdat, 0, sizeof(sdat));
     memset(&opt, 0, sizeof(opt));
-    opt.sect = true;	/* by def load sector */
-    opt.maps = true;	/* by def map sector */
-    opt.hand = true;	/* by def prepare handover */
+    opt.sect = true;	/* by def. load sector */
+    opt.maps = true;	/* by def. map sector */
+    opt.hand = true;	/* by def. prepare handover */
+    opt.chain = true;	/* by def. do chainload */
     opt.foff = opt.soff = opt.fip = opt.sip = 0x7C00;
     opt.drivename = "boot";
 #ifdef DEBUG
@@ -777,7 +778,7 @@ int main(int argc, char *argv[])
 	goto bail;
 
     /*
-     * Prepare boot-time mmap data We should to it here, as manglers could
+     * Prepare boot-time mmap data. We should to it here, as manglers could
      * potentially alter some of the data.
      */
 
@@ -806,7 +807,10 @@ int main(int argc, char *argv[])
 	wait_key();
     }
 
-    do_boot(data, ndata);
+    if (ndata && opt.chain) /* boot only if we actually chainload */
+	do_boot(data, ndata);
+    else
+	error("Service-only run completed, exiting.\n");
 bail:
     pi_del(&iter);
     /* Free allocated areas */
diff --git a/com32/chain/options.c b/com32/chain/options.c
index 2c3d0ff8..53810da7 100644
--- a/com32/chain/options.c
+++ b/com32/chain/options.c
@@ -65,10 +65,6 @@ Usage:\n\
     chain.c32 fs [options]\n\
 ", "\
 \nOptions ('no' prefix specifies default value):\n\
-    file=<file>          Load and execute <file>\n\
-    seg=<s[:o[:i]]>      Load file at <s:o>, jump to <s:i>\n\
-                         - defaults to 0:0x7C00:0x7C00\n\
-                         - ommited o/i values default to 0\n\
     sect[=<s[:o[:i]]>]   Load sector at <s:o>, jump to <s:i>\n\
                          - defaults to 0:0x7C00:0x7C00\n\
                          - ommited o/i values default to 0x7C00\n\
@@ -78,17 +74,23 @@ Usage:\n\
     nosave               Write adjusted sector back to disk\n\
     hand                 Prepare handover area\n\
     nohptr               Force ds:si and ds:bp to point to handover area\n\
-    bss=<filename>       Emulate syslinux's BSS\n\
-    bs=<filename>        Emulate syslinux's BS\n\
     noswap               Swap drive numbers, if bootdisk is not fd0/hd0\n\
-    nohide               Hide primary partitions, unhide selected partition\n\
-    nohideall            Hide *all* partitions, unhide selected partition\n\
+    nohide               Disable all hide variations (also the default)\n\
+    hide                 Hide primary partitions, unhide selected partition\n\
+    hideall              Hide *all* partitions, unhide selected partition\n\
+    unhide               Unhide primary partitions\n\
+    unhideall            Unhide *all* partitions\n\
     nombrchs             Walk *all* partitions and fix E/MBRs' chs values\n\
     nokeeppxe            Keep the PXE and UNDI stacks in memory (PXELINUX)\n\
     nowarn               Wait for a keypress to continue chainloading\n\
                          - useful to see emited warnings\n\
+    chain                Actually perform the chainloading\n\
 ", "\
 \nOptions continued ...\n\
+    file=<file>          Load and execute <file>\n\
+    seg=<s[:o[:i]]>      Load file at <s:o>, jump to <s:i>\n\
+                         - defaults to 0:0x7C00:0x7C00\n\
+                         - ommited o/i values default to 0\n\
     isolinux=<loader>    Load another version of ISOLINUX\n\
     ntldr=<loader>       Load Windows NTLDR, SETUPLDR.BIN or BOOTMGR\n\
     cmldr=<loader>       Load Recovery Console of Windows NT/2K/XP/2003\n\
@@ -100,6 +102,8 @@ Usage:\n\
     grub=<loader>        Load GRUB Legacy stage2\n\
     grubcfg=<filename>   Set alternative config filename for GRUB Legacy\n\
     grldr=<loader>       Load GRUB4DOS grldr\n\
+    bss=<filename>       Emulate syslinux's BSS\n\
+    bs=<filename>        Emulate syslinux's BS\n\
 \nPlease see doc/chain.txt for the detailed documentation.\n\
 "
     };
@@ -268,6 +272,13 @@ int parse_args(int argc, char *argv[])
 	    opt.warn = true;
 	} else if (!strcmp(argv[i], "nowarn")) {
 	    opt.warn = false;
+	} else if (!strcmp(argv[i], "chain")) {
+	    opt.chain = true;
+	} else if (!strcmp(argv[i], "nochain")) {
+	    opt.chain = false;
+	    opt.file = NULL;
+	    opt.maps = false;
+	    opt.hand = false;
 	} else if (((argv[i][0] == 'h' || argv[i][0] == 'f')
 		    && argv[i][1] == 'd')
 		   || !strncmp(argv[i], "mbr:", 4)
@@ -302,10 +313,12 @@ int parse_args(int argc, char *argv[])
 	goto bail;
     }
 
+#if 0
     if ((!opt.maps || !opt.sect) && !opt.file) {
 	error("You have to load something.\n");
 	goto bail;
     }
+#endif
 
     if (opt.filebpb && !opt.file) {
 	error("Option 'filebpb' requires a file.\n");
diff --git a/com32/chain/options.h b/com32/chain/options.h
index ee15768c..bc244f60 100644
--- a/com32/chain/options.h
+++ b/com32/chain/options.h
@@ -29,6 +29,7 @@ struct options {
     bool filebpb;
     bool mbrchs;
     bool warn;
+    bool chain;
     uint16_t keeppxe;
     struct syslinux_rm_regs regs;
 };