lmdb: added mdb_env_open_ex() and exclusive/monopoly mode for mdb_chk.

Change-Id: I867e7f17924ffecb744440e95db96c0a7411d6ef

lmdb.h

@@ -616,7 +616,7 @@ int  mdb_env_create(MDB_env **env);
 	 * </ul>
 	 */
 int  mdb_env_open(MDB_env *env, const char *path, unsigned flags, mode_t mode);
-
+int  mdb_env_open_ex(MDB_env *env, const char *path, unsigned flags, mode_t mode, int *exclusive);
 	/** @brief Copy an LMDB environment to the specified path.
 	 *
 	 * This function may be used to make a backup of an existing environment.

mdb.c

@@ -4345,8 +4345,6 @@ mdb_env_share_locks(MDB_env *env, int *excl, MDB_meta *meta)
 	struct flock lock_info;
 	int rc = 0;
 
-	env->me_txns->mti_txnid = meta->mm_txnid;
-
 	/* The shared lock replaces the existing lock */
 	memset((void *)&lock_info, 0, sizeof(lock_info));
 	lock_info.l_type = F_RDLCK;
@@ -4600,6 +4598,12 @@ fail:
 
 int ESECT
 mdb_env_open(MDB_env *env, const char *path, unsigned flags, mode_t mode)
+{
+	return mdb_env_open_ex(env, path, flags, mode, NULL);
+}
+
+int ESECT
+mdb_env_open_ex(MDB_env *env, const char *path, unsigned flags, mode_t mode, int *exclusive)
 {
 	int		oflags, rc, len, excl = -1;
 	char *lpath, *dpath;
@@ -4678,9 +4682,17 @@ mdb_env_open(MDB_env *env, const char *path, unsigned flags, mode_t mode)
 	if ((rc = mdb_env_open2(env, &meta)) == MDB_SUCCESS) {
 		mdb_debug("opened dbenv %p", (void *) env);
 		if (excl > 0) {
-			rc = mdb_env_share_locks(env, &excl, &meta);
+			env->me_txns->mti_txnid = meta.mm_txnid;
-			if (rc)
+			if (exclusive == NULL || *exclusive < 2) {
-				goto leave;
+				/* LY: downgrade lock only if exclusive access not requested.
+				 *     in case exclusive==1, just leave value as is. */
+				rc = mdb_env_share_locks(env, &excl, &meta);
+				if (rc)
+					goto leave;
+			}
+		} else if (exclusive) {
+			/* LY: just indicate that is not an exclusive access. */
+			*exclusive = 0;
 		}
 		if (!(flags & MDB_RDONLY)) {
 			MDB_txn *txn;

mdb_chk.c

@@ -61,6 +61,7 @@ size_t dbi_payload_bytes[MAX_DBI];
 short *pagemap;
 size_t pgcount;
 size_t total_payload_bytes, total_unused_bytes;
+int exclusive = 2;
 
 MDB_env *env;
 MDB_txn *txn, *locktxn;
@@ -458,7 +459,8 @@ static void usage(char *prog)
 			"  -v\tmore verbose, could be used multiple times\n"
 			"  -n\tNOSUBDIR mode for open\n"
 			"  -q\tbe quiet\n"
-			"  -w\tstart write-txn to lock db\n", prog);
+			"  -w\tstart write-txn to lock db\n"
+			"  -c\tforce cooperative mode (don't try exclusive)\n", prog);
 	exit(EXIT_FAILURE);
 }
 
@@ -474,7 +476,7 @@ const char* meta_synctype(size_t sign) {
 }
 
 int meta_lt(size_t txn1, size_t sign1, size_t txn2, size_t sign2) {
-	return ((sign1 > 1) == (sign2 > 1)) ? txn1 < txn2 : sign2 > 1;
+	return ((sign1 > 1) == (sign2 > 1)) ? txn1 < txn2 : txn2 && sign2 > 1;
 }
 
 int main(int argc, char *argv[])
@@ -491,7 +493,7 @@ int main(int argc, char *argv[])
 		usage(prog);
 	}
 
-	while ((i = getopt(argc, argv, "Vvqnw")) != EOF) {
+	while ((i = getopt(argc, argv, "Vvqnwc")) != EOF) {
 		switch(i) {
 		case 'V':
 			printf("%s\n", MDB_VERSION_STRING);
@@ -509,6 +511,9 @@ int main(int argc, char *argv[])
 		case 'w':
 			envflags &= ~MDB_RDONLY;
 			break;
+		case 'c':
+			exclusive = 0;
+			break;
 		default:
 			usage(prog);
 		}
@@ -545,11 +550,13 @@ int main(int argc, char *argv[])
 
 	mdb_env_set_maxdbs(env, 3);
 
-	rc = mdb_env_open(env, envname, envflags, 0664);
+	rc = mdb_env_open_ex(env, envname, envflags, 0664, &exclusive);
 	if (rc) {
 		error("mdb_env_open failed, error %d %s\n", rc, mdb_strerror(rc));
 		goto bailout;
 	}
+	if (verbose)
+		print(" - %s mode\n", exclusive ? "monopolistic" : "cooperative");
 
 	rc = mdb_txn_begin(env, NULL, MDB_RDONLY, &txn);
 	if (rc) {
@@ -619,18 +626,20 @@ int main(int argc, char *argv[])
 			  info.me_meta2_txnid, info.me_last_txnid);
 	}
 
-	if (! meta_lt(info.me_meta1_txnid, info.me_meta1_sign,
+	if (exclusive > 1) {
-			info.me_meta2_txnid, info.me_meta2_sign)
+		if (! meta_lt(info.me_meta1_txnid, info.me_meta1_sign,
-		&& info.me_meta1_txnid != info.me_last_txnid) {
+				info.me_meta2_txnid, info.me_meta2_sign)
-		print(" - meta-1 txn-id mismatch\n");
+			&& info.me_meta1_txnid != info.me_last_txnid) {
-		++problems_meta;
+			print(" - meta-1 txn-id mismatch\n");
-	}
+			++problems_meta;
+		}
 
-	if (! meta_lt(info.me_meta2_txnid, info.me_meta2_sign,
+		if (! meta_lt(info.me_meta2_txnid, info.me_meta2_sign,
-			info.me_meta1_txnid, info.me_meta1_sign)
+				info.me_meta1_txnid, info.me_meta1_sign)
-		&& info.me_meta2_txnid != info.me_last_txnid) {
+			&& info.me_meta2_txnid != info.me_last_txnid) {
-		print(" - meta-2 txn-id mismatch\n");
+			print(" - meta-2 txn-id mismatch\n");
-		++problems_meta;
+			++problems_meta;
+		}
 	}
 
 	print("Walking b-tree...\n");