ITS#8704 add MDB_PREVSNAPSHOT flag to mdb_env_open

used to open the previous snapshot, in case the latest one
is corrupted

1 files changed, 29 insertions, 12 deletions

diff --git a/external/db_drivers/liblmdb/mdb.c b/external/db_drivers/liblmdb/mdb.c
index 3552bd2a9..377512ebe 100644
--- a/external/db_drivers/liblmdb/mdb.c
+++ b/external/db_drivers/liblmdb/mdb.c
@@ -1468,7 +1468,7 @@ static int	mdb_page_merge(MDB_cursor *csrc, MDB_cursor *cdst);
 static int	mdb_page_split(MDB_cursor *mc, MDB_val *newkey, MDB_val *newdata,
 				pgno_t newpgno, unsigned int nflags);
 
-static int  mdb_env_read_header(MDB_env *env, MDB_meta *meta);
+static int  mdb_env_read_header(MDB_env *env, int prev, MDB_meta *meta);
 static MDB_meta *mdb_env_pick_meta(const MDB_env *env);
 static int  mdb_env_write_meta(MDB_txn *txn);
 #ifdef MDB_USE_POSIX_MUTEX /* Drop unused excl arg */
@@ -3632,6 +3632,8 @@ done:
 	return MDB_SUCCESS;
 }
 
+static int ESECT mdb_env_share_locks(MDB_env *env, int *excl);
+
 int
 mdb_txn_commit(MDB_txn *txn)
 {
@@ -3854,6 +3856,15 @@ mdb_txn_commit(MDB_txn *txn)
 	if ((rc = mdb_env_write_meta(txn)))
 		goto fail;
 	end_mode = MDB_END_COMMITTED|MDB_END_UPDATE;
+	if (env->me_flags & MDB_PREVSNAPSHOT) {
+		if (!(env->me_flags & MDB_NOLOCK)) {
+			int excl;
+			rc = mdb_env_share_locks(env, &excl);
+			if (rc)
+				goto fail;
+		}
+		env->me_flags ^= MDB_PREVSNAPSHOT;
+	}
 
 done:
 	mdb_txn_end(txn, end_mode);
@@ -3867,11 +3878,12 @@ fail:
 /** Read the environment parameters of a DB environment before
  * mapping it into memory.
  * @param[in] env the environment handle
+ * @param[in] prev whether to read the backup meta page
  * @param[out] meta address of where to store the meta information
  * @return 0 on success, non-zero on failure.
  */
 static int ESECT
-mdb_env_read_header(MDB_env *env, MDB_meta *meta)
+mdb_env_read_header(MDB_env *env, int prev, MDB_meta *meta)
 {
 	MDB_metabuf	pbuf;
 	MDB_page	*p;
@@ -3922,7 +3934,7 @@ mdb_env_read_header(MDB_env *env, MDB_meta *meta)
 			return MDB_VERSION_MISMATCH;
 		}
 
-		if (off == 0 || m->mm_txnid > meta->mm_txnid)
+		if (off == 0 || (prev ? m->mm_txnid < meta->mm_txnid : m->mm_txnid > meta->mm_txnid))
 			*meta = *m;
 	}
 	return 0;
@@ -4131,7 +4143,8 @@ static MDB_meta *
 mdb_env_pick_meta(const MDB_env *env)
 {
 	MDB_meta *const *metas = env->me_metas;
-	return metas[ metas[0]->mm_txnid < metas[1]->mm_txnid ];
+	return metas[ (metas[0]->mm_txnid < metas[1]->mm_txnid) ^
+		((env->me_flags & MDB_PREVSNAPSHOT) != 0) ];
 }
 
 int ESECT
@@ -4366,7 +4379,7 @@ mdb_fsize(HANDLE fd, mdb_size_t *size)
 /** Further setup required for opening an LMDB environment
  */
 static int ESECT
-mdb_env_open2(MDB_env *env)
+mdb_env_open2(MDB_env *env, int prev)
 {
 	unsigned int flags = env->me_flags;
 	int i, newenv = 0, rc;
@@ -4429,7 +4442,7 @@ mdb_env_open2(MDB_env *env)
 	}
 #endif
 
-	if ((i = mdb_env_read_header(env, &meta)) != 0) {
+	if ((i = mdb_env_read_header(env, prev, &meta)) != 0) {
 		if (i != ENOENT)
 			return i;
 		DPUTS("new mdbenv");
@@ -4505,6 +4518,9 @@ mdb_env_open2(MDB_env *env)
 #endif
 	env->me_maxpg = env->me_mapsize / env->me_psize;
 
+	if (env->me_txns)
+		env->me_txns->mti_txnid = meta.mm_txnid;
+
 #if MDB_DEBUG
 	{
 		MDB_meta *meta = mdb_env_pick_meta(env);
@@ -4600,9 +4616,6 @@ static int ESECT
 mdb_env_share_locks(MDB_env *env, int *excl)
 {
 	int rc = 0;
-	MDB_meta *meta = mdb_env_pick_meta(env);
-
-	env->me_txns->mti_txnid = meta->mm_txnid;
 
 #ifdef _WIN32
 	{
@@ -5056,7 +5069,7 @@ fail:
 	 */
 #define	CHANGEABLE	(MDB_NOSYNC|MDB_NOMETASYNC|MDB_MAPASYNC|MDB_NOMEMINIT)
 #define	CHANGELESS	(MDB_FIXEDMAP|MDB_NOSUBDIR|MDB_RDONLY| \
-	MDB_WRITEMAP|MDB_NOTLS|MDB_NOLOCK|MDB_NORDAHEAD)
+	MDB_WRITEMAP|MDB_NOTLS|MDB_NOLOCK|MDB_NORDAHEAD|MDB_PREVSNAPSHOT)
 
 #if VALID_FLAGS & PERSISTENT_FLAGS & (CHANGEABLE|CHANGELESS)
 # error "Persistent DB flags & env flags overlap, but both go in mm_flags"
@@ -5178,9 +5191,13 @@ mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mdb_mode_t mode
 		rc = mdb_env_setup_locks(env, lpath, mode, &excl);
 		if (rc)
 			goto leave;
+		if ((flags & MDB_PREVSNAPSHOT) && !excl) {
+			rc = EAGAIN;
+			goto leave;
+		}
 	}
 
-	if ((rc = mdb_env_open2(env)) == MDB_SUCCESS) {
+	if ((rc = mdb_env_open2(env, flags & MDB_PREVSNAPSHOT)) == MDB_SUCCESS) {
 		if (flags & (MDB_RDONLY|MDB_WRITEMAP)) {
 			env->me_mfd = env->me_fd;
 		} else {
@@ -5206,7 +5223,7 @@ mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mdb_mode_t mode
 			}
 		}
 		DPRINTF(("opened dbenv %p", (void *) env));
-		if (excl > 0) {
+		if (excl > 0 && !(flags & MDB_PREVSNAPSHOT)) {
 			rc = mdb_env_share_locks(env, &excl);
 			if (rc)
 				goto leave;