tdb: introduce TDB_SUPPORTED_FEATURE_FLAGS

This will allow to store a feature mask in the tdb header on disk,
so that openers can check if they can handle the features
other openers are using.

Pair-Programmed-With: Volker Lendecke <vl@samba.org>
Pair-Programmed-With: Michael Adam <obnox@samba.org>
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Volker Lendecke <vl@samba.org>
Signed-off-by: Michael Adam <obnox@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>

4 files changed, 39 insertions, 2 deletions

diff --git a/lib/tdb/common/check.c b/lib/tdb/common/check.c
index 9f9d8708c1e..e632af51536 100644
--- a/lib/tdb/common/check.c
+++ b/lib/tdb/common/check.c
@@ -39,7 +39,9 @@ static bool tdb_check_header(struct tdb_context *tdb, tdb_off_t *recovery)
 	if (hdr.version != TDB_VERSION)
 		goto corrupt;
 
-	if (hdr.rwlocks != 0 && hdr.rwlocks != TDB_HASH_RWLOCK_MAGIC)
+	if (hdr.rwlocks != 0 &&
+	    hdr.rwlocks != TDB_FEATURE_FLAG_MAGIC &&
+	    hdr.rwlocks != TDB_HASH_RWLOCK_MAGIC)
 		goto corrupt;
 
 	tdb_header_hash(tdb, &h1, &h2);
diff --git a/lib/tdb/common/open.c b/lib/tdb/common/open.c
index d5c04321111..17ab0b7c285 100644
--- a/lib/tdb/common/open.c
+++ b/lib/tdb/common/open.c
@@ -76,6 +76,20 @@ static int tdb_new_database(struct tdb_context *tdb, struct tdb_header *header,
 	if (tdb->flags & TDB_INCOMPATIBLE_HASH)
 		newdb->rwlocks = TDB_HASH_RWLOCK_MAGIC;
 
+	/*
+	 * If we have any features we add the FEATURE_FLAG_MAGIC, overwriting the
+	 * TDB_HASH_RWLOCK_MAGIC above.
+	 */
+	if (newdb->feature_flags != 0) {
+		newdb->rwlocks = TDB_FEATURE_FLAG_MAGIC;
+	}
+
+	/*
+	 * It's required for some following code pathes
+	 * to have the fields on 'tdb' up-to-date.
+	 */
+	tdb->feature_flags = newdb->feature_flags;
+
 	if (tdb->flags & TDB_INTERNAL) {
 		tdb->map_size = size;
 		tdb->map_ptr = (char *)newdb;
@@ -390,6 +404,7 @@ _PUBLIC_ struct tdb_context *tdb_open_ex(const char *name, int hash_size, int td
 		goto fail;
 
 	if (header.rwlocks != 0 &&
+	    header.rwlocks != TDB_FEATURE_FLAG_MAGIC &&
 	    header.rwlocks != TDB_HASH_RWLOCK_MAGIC) {
 		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_open_ex: spinlocks no longer supported\n"));
 		errno = ENOSYS;
@@ -397,6 +412,19 @@ _PUBLIC_ struct tdb_context *tdb_open_ex(const char *name, int hash_size, int td
 	}
 	tdb->hash_size = header.hash_size;
 
+	if (header.rwlocks == TDB_FEATURE_FLAG_MAGIC) {
+		tdb->feature_flags = header.feature_flags;
+	}
+
+	if (tdb->feature_flags & ~TDB_SUPPORTED_FEATURE_FLAGS) {
+		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_open_ex: unsupported "
+			 "features in tdb %s: 0x%08x (supported: 0x%08x)\n",
+			 name, (unsigned)tdb->feature_flags,
+			 (unsigned)TDB_SUPPORTED_FEATURE_FLAGS));
+		errno = ENOSYS;
+		goto fail;
+	}
+
 	if ((header.magic1_hash == 0) && (header.magic2_hash == 0)) {
 		/* older TDB without magic hash references */
 		tdb->hash_fn = tdb_old_hash;
diff --git a/lib/tdb/common/summary.c b/lib/tdb/common/summary.c
index 22404afa9b8..6f2e0a9e80a 100644
--- a/lib/tdb/common/summary.c
+++ b/lib/tdb/common/summary.c
@@ -21,6 +21,7 @@
 	"Size of file/data: %u/%zu\n" \
 	"Number of records: %zu\n" \
 	"Incompatible hash: %s\n" \
+	"Active/supported feature flags: 0x%08x/0x%08x\n" \
 	"Smallest/average/largest keys: %zu/%zu/%zu\n" \
 	"Smallest/average/largest data: %zu/%zu/%zu\n" \
 	"Smallest/average/largest padding: %zu/%zu/%zu\n" \
@@ -169,6 +170,7 @@ _PUBLIC_ char *tdb_summary(struct tdb_context *tdb)
 		 tdb->map_size, keys.total+data.total,
 		 keys.num,
 		 (tdb->hash_fn == tdb_jenkins_hash)?"yes":"no",
+		 (unsigned)tdb->feature_flags, TDB_SUPPORTED_FEATURE_FLAGS,
 		 keys.min, tally_mean(&keys), keys.max,
 		 data.min, tally_mean(&data), data.max,
 		 extra.min, tally_mean(&extra), extra.max,
diff --git a/lib/tdb/common/tdb_private.h b/lib/tdb/common/tdb_private.h
index a6721595782..aa9dd55ba47 100644
--- a/lib/tdb/common/tdb_private.h
+++ b/lib/tdb/common/tdb_private.h
@@ -53,6 +53,7 @@ typedef uint32_t tdb_off_t;
 #define TDB_RECOVERY_MAGIC (0xf53bc0e7U)
 #define TDB_RECOVERY_INVALID_MAGIC (0x0)
 #define TDB_HASH_RWLOCK_MAGIC (0xbad1a51U)
+#define TDB_FEATURE_FLAG_MAGIC (0xbad1a52U)
 #define TDB_ALIGNMENT 4
 #define DEFAULT_HASH_SIZE 131
 #define FREELIST_TOP (sizeof(struct tdb_header))
@@ -68,6 +69,8 @@ typedef uint32_t tdb_off_t;
 #define TDB_PAD_BYTE 0x42
 #define TDB_PAD_U32  0x42424242
 
+#define TDB_SUPPORTED_FEATURE_FLAGS 0
+
 /* NB assumes there is a local variable called "tdb" that is the
  * current context, also takes doubly-parenthesized print-style
  * argument. */
@@ -152,7 +155,8 @@ struct tdb_header {
 	tdb_off_t sequence_number; /* used when TDB_SEQNUM is set */
 	uint32_t magic1_hash; /* hash of TDB_MAGIC_FOOD. */
 	uint32_t magic2_hash; /* hash of TDB_MAGIC. */
-	tdb_off_t reserved[27];
+	uint32_t feature_flags;
+	tdb_off_t reserved[26];
 };
 
 struct tdb_lock_type {
@@ -200,6 +204,7 @@ struct tdb_context {
 	int lockrecs_array_length;
 	enum TDB_ERROR ecode; /* error code for last tdb error */
 	uint32_t hash_size;
+	uint32_t feature_flags;
 	uint32_t flags; /* the flags passed to tdb_open */
 	struct tdb_traverse_lock travlocks; /* current traversal locks */
 	struct tdb_context *next; /* all tdbs to avoid multiple opens */