From: Rusty Russell <rusty@rustcorp.com.au>
Date: Tue, 18 Aug 2009 04:07:47 +0000 (+0930)
Subject: tdb: locking cleanup
X-Git-Url: https://git.ozlabs.org/?p=ccan;a=commitdiff_plain;h=b2c0ebc6f53b05b222937991f100f8a89701f9b1

tdb: locking cleanup

Explicitly split lock and unlock, for future replacement with user-supplied functions.
Use explicit flags enum for marking, blocking and probing.
Indicate upon unlock whether we had a read or write lock (POSIX doesn't care, but
wrappers might, and it's nice to be explicit).
---

diff --git a/ccan/tdb/io.c b/ccan/tdb/io.c
index 59caa5dd..ca7d0819 100644
--- a/ccan/tdb/io.c
+++ b/ccan/tdb/io.c
@@ -460,7 +460,8 @@ static const struct tdb_methods io_methods = {
 	tdb_next_hash_chain,
 	tdb_oob,
 	tdb_expand_file,
-	tdb_brlock
+	tdb_brlock,
+	tdb_brunlock
 };
 
 /*
diff --git a/ccan/tdb/lock.c b/ccan/tdb/lock.c
index 07545b34..e6b900e4 100644
--- a/ccan/tdb/lock.c
+++ b/ccan/tdb/lock.c
@@ -27,13 +27,98 @@
 
 #include "tdb_private.h"
 
-#define TDB_MARK_LOCK 0x80000000
-
 void tdb_setalarm_sigptr(struct tdb_context *tdb, volatile sig_atomic_t *ptr)
 {
 	tdb->interrupt_sig_ptr = ptr;
 }
 
+static int fcntl_lock(struct tdb_context *tdb,
+		      int rw, off_t off, off_t len, bool wait)
+{
+	struct flock fl;
+	
+	fl.l_type = rw;
+	fl.l_whence = SEEK_SET;
+	fl.l_start = off;
+	fl.l_len = len;
+	fl.l_pid = 0;
+
+	if (wait)
+		return fcntl(tdb->fd, F_SETLKW, &fl);
+	else
+		return fcntl(tdb->fd, F_SETLK, &fl);
+}
+
+static int fcntl_unlock(struct tdb_context *tdb, int rw, off_t off, off_t len)
+{
+	struct flock fl;
+#if 0 /* Check they matched up locks and unlocks correctly. */
+	char line[80];
+	FILE *locks;
+	bool found = false;
+
+	locks = fopen("/proc/locks", "r");
+
+	while (fgets(line, 80, locks)) {
+		char *p;
+		int type, start, l;
+
+		/* eg. 1: FLOCK  ADVISORY  WRITE 2440 08:01:2180826 0 EOF */
+		p = strchr(line, ':') + 1;
+		if (strncmp(p, " POSIX  ADVISORY  ", strlen(" POSIX  ADVISORY  ")))
+			continue;
+		p += strlen(" FLOCK  ADVISORY  ");
+		if (strncmp(p, "READ  ", strlen("READ  ")) == 0)
+			type = F_RDLCK;
+		else if (strncmp(p, "WRITE ", strlen("WRITE ")) == 0)
+			type = F_WRLCK;
+		else
+			abort();
+		p += 6;
+		if (atoi(p) != getpid())
+			continue;
+		p = strchr(strchr(p, ' ') + 1, ' ') + 1;
+		start = atoi(p);
+		p = strchr(p, ' ') + 1;
+		if (strncmp(p, "EOF", 3) == 0)
+			l = 0;
+		else
+			l = atoi(p) - start + 1;
+
+		if (off == start) {
+			if (len != l) {
+				fprintf(stderr, "Len %u should be %u: %s",
+					(int)len, l, line);
+				abort();
+			}
+			if (type != rw) {
+				fprintf(stderr, "Type %s wrong: %s",
+					rw == F_RDLCK ? "READ" : "WRITE", line);
+				abort();
+			}
+			found = true;
+			break;
+		}
+	}
+
+	if (!found) {
+		fprintf(stderr, "Unlock on %u@%u not found!\n",
+			(int)off, (int)len);
+		abort();
+	}
+
+	fclose(locks);
+#endif
+
+	fl.l_type = F_UNLCK;
+	fl.l_whence = SEEK_SET;
+	fl.l_start = off;
+	fl.l_len = len;
+	fl.l_pid = 0;
+
+	return fcntl(tdb->fd, F_SETLKW, &fl);
+}
+
 /* a byte range locking function - return 0 on success
    this functions locks/unlocks 1 byte at the specified offset.
 
@@ -42,30 +127,28 @@ void tdb_setalarm_sigptr(struct tdb_context *tdb, volatile sig_atomic_t *ptr)
 
    note that a len of zero means lock to end of file
 */
-int tdb_brlock(struct tdb_context *tdb, tdb_off_t offset, 
-	       int rw_type, int lck_type, int probe, size_t len)
+int tdb_brlock(struct tdb_context *tdb,
+	       int rw_type, tdb_off_t offset, size_t len,
+	       enum tdb_lock_flags flags)
 {
-	struct flock fl;
 	int ret;
 
 	if (tdb->flags & TDB_NOLOCK) {
 		return 0;
 	}
 
+	if (flags & TDB_LOCK_MARK_ONLY) {
+		return 0;
+	}
+
 	if ((rw_type == F_WRLCK) && (tdb->read_only || tdb->traverse_read)) {
 		tdb->ecode = TDB_ERR_RDONLY;
 		return -1;
 	}
 
-	fl.l_type = rw_type;
-	fl.l_whence = SEEK_SET;
-	fl.l_start = offset;
-	fl.l_len = len;
-	fl.l_pid = 0;
-
 	do {
-		ret = fcntl(tdb->fd,lck_type,&fl);
-
+		ret = fcntl_lock(tdb, rw_type, offset, len,
+				 flags & TDB_LOCK_WAIT);
 		/* Check for a sigalarm break. */
 		if (ret == -1 && errno == EINTR &&
 				tdb->interrupt_sig_ptr &&
@@ -78,17 +161,36 @@ int tdb_brlock(struct tdb_context *tdb, tdb_off_t offset,
 		/* Generic lock error. errno set by fcntl.
 		 * EAGAIN is an expected return from non-blocking
 		 * locks. */
-		if (!probe && lck_type != F_SETLK) {
+		if (!(flags & TDB_LOCK_PROBE) && errno != EAGAIN) {
 			/* Ensure error code is set for log fun to examine. */
 			tdb->ecode = TDB_ERR_LOCK;
-			TDB_LOG((tdb, TDB_DEBUG_TRACE,"tdb_brlock failed (fd=%d) at offset %d rw_type=%d lck_type=%d len=%d\n", 
-				 tdb->fd, offset, rw_type, lck_type, (int)len));
+			TDB_LOG((tdb, TDB_DEBUG_TRACE,"tdb_brlock failed (fd=%d) at offset %d rw_type=%d flags=%d len=%d\n", 
+				 tdb->fd, offset, rw_type, flags, (int)len));
 		}
 		return -1;
 	}
 	return 0;
 }
 
+int tdb_brunlock(struct tdb_context *tdb,
+		 int rw_type, tdb_off_t offset, size_t len)
+{
+	int ret;
+
+	if (tdb->flags & TDB_NOLOCK) {
+		return 0;
+	}
+
+	do {
+		ret = fcntl_unlock(tdb, rw_type, offset, len);
+	} while (ret == -1 && errno == EINTR);
+
+	if (ret == -1) {
+		TDB_LOG((tdb, TDB_DEBUG_TRACE,"tdb_brunlock failed (fd=%d) at offset %d rw_type=%d len=%d\n", 
+			 tdb->fd, offset, rw_type, (int)len));
+	}
+	return ret;
+}
 
 /*
   upgrade a read lock to a write lock. This needs to be handled in a
@@ -101,7 +203,8 @@ int tdb_brlock_upgrade(struct tdb_context *tdb, tdb_off_t offset, size_t len)
 	int count = 1000;
 	while (count--) {
 		struct timeval tv;
-		if (tdb_brlock(tdb, offset, F_WRLCK, F_SETLKW, 1, len) == 0) {
+		if (tdb_brlock(tdb, F_WRLCK, offset, len,
+			       TDB_LOCK_WAIT|TDB_LOCK_PROBE) == 0) {
 			return 0;
 		}
 		if (errno != EDEADLK) {
@@ -118,13 +221,11 @@ int tdb_brlock_upgrade(struct tdb_context *tdb, tdb_off_t offset, size_t len)
 
 
 /* lock a list in the database. list -1 is the alloc list */
-static int _tdb_lock(struct tdb_context *tdb, int list, int ltype, int op)
+static int _tdb_lock(struct tdb_context *tdb, int list, int ltype,
+		     enum tdb_lock_flags flags)
 {
 	struct tdb_lock_type *new_lck;
 	int i;
-	bool mark_lock = ((ltype & TDB_MARK_LOCK) == TDB_MARK_LOCK);
-
-	ltype &= ~TDB_MARK_LOCK;
 
 	/* a global lock allows us to avoid per chain locks */
 	if (tdb->global_lock.count && 
@@ -176,9 +277,7 @@ static int _tdb_lock(struct tdb_context *tdb, int list, int ltype, int op)
 
 	/* Since fcntl locks don't nest, we do a lock for the first one,
 	   and simply bump the count for future ones */
-	if (!mark_lock &&
-	    tdb->methods->tdb_brlock(tdb,FREELIST_TOP+4*list, ltype, op,
-				     0, 1)) {
+	if (tdb->methods->brlock(tdb, ltype, FREELIST_TOP+4*list, 1, flags)) {
 		return -1;
 	}
 
@@ -196,7 +295,8 @@ static int _tdb_lock(struct tdb_context *tdb, int list, int ltype, int op)
 int tdb_lock(struct tdb_context *tdb, int list, int ltype)
 {
 	int ret;
-	ret = _tdb_lock(tdb, list, ltype, F_SETLKW);
+
+	ret = _tdb_lock(tdb, list, ltype, TDB_LOCK_WAIT);
 	if (ret) {
 		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_lock failed on list %d "
 			 "ltype=%d (%s)\n",  list, ltype, strerror(errno)));
@@ -207,21 +307,16 @@ int tdb_lock(struct tdb_context *tdb, int list, int ltype)
 /* lock a list in the database. list -1 is the alloc list. non-blocking lock */
 int tdb_lock_nonblock(struct tdb_context *tdb, int list, int ltype)
 {
-	return _tdb_lock(tdb, list, ltype, F_SETLK);
+	return _tdb_lock(tdb, list, ltype, TDB_LOCK_NOWAIT);
 }
 
 
-/* unlock the database: returns void because it's too late for errors. */
-	/* changed to return int it may be interesting to know there
-	   has been an error  --simo */
-int tdb_unlock(struct tdb_context *tdb, int list, int ltype)
+static int _tdb_unlock(struct tdb_context *tdb, int list, int ltype,
+		       bool mark_lock)
 {
 	int ret = -1;
 	int i;
 	struct tdb_lock_type *lck = NULL;
-	bool mark_lock = ((ltype & TDB_MARK_LOCK) == TDB_MARK_LOCK);
-
-	ltype &= ~TDB_MARK_LOCK;
 
 	/* a global lock allows us to avoid per chain locks */
 	if (tdb->global_lock.count && 
@@ -270,8 +365,8 @@ int tdb_unlock(struct tdb_context *tdb, int list, int ltype)
 	if (mark_lock) {
 		ret = 0;
 	} else {
-		ret = tdb->methods->tdb_brlock(tdb, FREELIST_TOP+4*list, F_UNLCK,
-					       F_SETLKW, 0, 1);
+		ret = tdb->methods->brunlock(tdb, ltype,
+					     FREELIST_TOP+4*list, 1);
 	}
 	tdb->num_locks--;
 
@@ -299,6 +394,11 @@ int tdb_unlock(struct tdb_context *tdb, int list, int ltype)
 	return ret;
 }
 
+int tdb_unlock(struct tdb_context *tdb, int list, int ltype)
+{
+	return _tdb_unlock(tdb, list, ltype, false);
+}
+
 /*
   get the transaction lock
  */
@@ -312,8 +412,7 @@ int tdb_transaction_lock(struct tdb_context *tdb, int ltype)
 		return 0;
 	}
 
-	if (tdb->methods->tdb_brlock(tdb, TRANSACTION_LOCK, ltype, 
-				     F_SETLKW, 0, 1) == -1) {
+	if (tdb->methods->brlock(tdb, ltype, TRANSACTION_LOCK, 1, TDB_LOCK_WAIT) == -1) {
 		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_lock: failed to get transaction lock\n"));
 		tdb->ecode = TDB_ERR_LOCK;
 		return -1;
@@ -325,7 +424,7 @@ int tdb_transaction_lock(struct tdb_context *tdb, int ltype)
 /*
   release the transaction lock
  */
-int tdb_transaction_unlock(struct tdb_context *tdb)
+int tdb_transaction_unlock(struct tdb_context *tdb, int ltype)
 {
 	int ret;
 	if (tdb->global_lock.count) {
@@ -335,7 +434,7 @@ int tdb_transaction_unlock(struct tdb_context *tdb)
 		tdb->transaction_lock_count--;
 		return 0;
 	}
-	ret = tdb->methods->tdb_brlock(tdb, TRANSACTION_LOCK, F_UNLCK, F_SETLKW, 0, 1);
+	ret = tdb->methods->brunlock(tdb, ltype, TRANSACTION_LOCK, 1);
 	if (ret == 0) {
 		tdb->transaction_lock_count = 0;
 	}
@@ -346,12 +445,9 @@ int tdb_transaction_unlock(struct tdb_context *tdb)
 
 
 /* lock/unlock entire database */
-static int _tdb_lockall(struct tdb_context *tdb, int ltype, int op)
+static int _tdb_lockall(struct tdb_context *tdb, int ltype,
+			enum tdb_lock_flags flags)
 {
-	bool mark_lock = ((ltype & TDB_MARK_LOCK) == TDB_MARK_LOCK);
-
-	ltype &= ~TDB_MARK_LOCK;
-
 	/* There are no locks on read-only dbs */
 	if (tdb->read_only || tdb->traverse_read) {
 		tdb->ecode = TDB_ERR_LOCK;
@@ -375,10 +471,10 @@ static int _tdb_lockall(struct tdb_context *tdb, int ltype, int op)
 		return -1;
 	}
 
-	if (!mark_lock &&
-	    tdb->methods->tdb_brlock(tdb, FREELIST_TOP, ltype, op,
-				     0, 4*tdb->header.hash_size)) {
-		if (op == F_SETLKW) {
+	if (tdb->methods->brlock(tdb, ltype,
+				 FREELIST_TOP, 4*tdb->header.hash_size,
+				 flags)) {
+		if (flags & TDB_LOCK_WAIT) {
 			TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_lockall failed (%s)\n", strerror(errno)));
 		}
 		return -1;
@@ -393,12 +489,8 @@ static int _tdb_lockall(struct tdb_context *tdb, int ltype, int op)
 
 
 /* unlock entire db */
-static int _tdb_unlockall(struct tdb_context *tdb, int ltype)
+static int _tdb_unlockall(struct tdb_context *tdb, int ltype, bool mark_lock)
 {
-	bool mark_lock = ((ltype & TDB_MARK_LOCK) == TDB_MARK_LOCK);
-
-	ltype &= ~TDB_MARK_LOCK;
-
 	/* There are no locks on read-only dbs */
 	if (tdb->read_only || tdb->traverse_read) {
 		tdb->ecode = TDB_ERR_LOCK;
@@ -416,8 +508,8 @@ static int _tdb_unlockall(struct tdb_context *tdb, int ltype)
 	}
 
 	if (!mark_lock &&
-	    tdb->methods->tdb_brlock(tdb, FREELIST_TOP, F_UNLCK, F_SETLKW, 
-				     0, 4*tdb->header.hash_size)) {
+	    tdb->methods->brunlock(tdb, F_WRLCK,
+				   FREELIST_TOP, 4*tdb->header.hash_size)) {
 		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_unlockall failed (%s)\n", strerror(errno)));
 		return -1;
 	}
@@ -432,27 +524,27 @@ static int _tdb_unlockall(struct tdb_context *tdb, int ltype)
 int tdb_lockall(struct tdb_context *tdb)
 {
 	tdb_trace(tdb, "tdb_lockall");
-	return _tdb_lockall(tdb, F_WRLCK, F_SETLKW);
+	return _tdb_lockall(tdb, F_WRLCK, TDB_LOCK_WAIT);
 }
 
 /* lock entire database with write lock - mark only */
 int tdb_lockall_mark(struct tdb_context *tdb)
 {
 	tdb_trace(tdb, "tdb_lockall_mark");
-	return _tdb_lockall(tdb, F_WRLCK | TDB_MARK_LOCK, F_SETLKW);
+	return _tdb_lockall(tdb, F_WRLCK, TDB_LOCK_MARK_ONLY);
 }
 
 /* unlock entire database with write lock - unmark only */
 int tdb_lockall_unmark(struct tdb_context *tdb)
 {
 	tdb_trace(tdb, "tdb_lockall_unmark");
-	return _tdb_unlockall(tdb, F_WRLCK | TDB_MARK_LOCK);
+	return _tdb_unlockall(tdb, F_WRLCK, true);
 }
 
 /* lock entire database with write lock - nonblocking varient */
 int tdb_lockall_nonblock(struct tdb_context *tdb)
 {
-	int ret = _tdb_lockall(tdb, F_WRLCK, F_SETLK);
+	int ret = _tdb_lockall(tdb, F_WRLCK, TDB_LOCK_NOWAIT);
 	tdb_trace_ret(tdb, "tdb_lockall_nonblock", ret);
 	return ret;
 }
@@ -461,20 +553,20 @@ int tdb_lockall_nonblock(struct tdb_context *tdb)
 int tdb_unlockall(struct tdb_context *tdb)
 {
 	tdb_trace(tdb, "tdb_unlockall");
-	return _tdb_unlockall(tdb, F_WRLCK);
+	return _tdb_unlockall(tdb, F_WRLCK, false);
 }
 
 /* lock entire database with read lock */
 int tdb_lockall_read(struct tdb_context *tdb)
 {
 	tdb_trace(tdb, "tdb_lockall_read");
-	return _tdb_lockall(tdb, F_RDLCK, F_SETLKW);
+	return _tdb_lockall(tdb, F_RDLCK, TDB_LOCK_WAIT);
 }
 
 /* lock entire database with read lock - nonblock varient */
 int tdb_lockall_read_nonblock(struct tdb_context *tdb)
 {
-	int ret = _tdb_lockall(tdb, F_RDLCK, F_SETLK);
+	int ret = _tdb_lockall(tdb, F_RDLCK, TDB_LOCK_NOWAIT);
 	tdb_trace_ret(tdb, "tdb_lockall_read_nonblock", ret);
 	return ret;
 }
@@ -483,7 +575,7 @@ int tdb_lockall_read_nonblock(struct tdb_context *tdb)
 int tdb_unlockall_read(struct tdb_context *tdb)
 {
 	tdb_trace(tdb, "tdb_unlockall_read");
-	return _tdb_unlockall(tdb, F_RDLCK);
+	return _tdb_unlockall(tdb, F_RDLCK, false);
 }
 
 /* lock/unlock one hash chain. This is meant to be used to reduce
@@ -508,7 +600,8 @@ int tdb_chainlock_nonblock(struct tdb_context *tdb, TDB_DATA key)
 /* mark a chain as locked without actually locking it. Warning! use with great caution! */
 int tdb_chainlock_mark(struct tdb_context *tdb, TDB_DATA key)
 {
-	int ret = tdb_lock(tdb, BUCKET(tdb->hash_fn(&key)), F_WRLCK | TDB_MARK_LOCK);
+	int ret = _tdb_lock(tdb, BUCKET(tdb->hash_fn(&key)), F_WRLCK,
+			    TDB_LOCK_MARK_ONLY);
 	tdb_trace_1rec(tdb, "tdb_chainlock_mark", key);
 	return ret;
 }
@@ -517,7 +610,7 @@ int tdb_chainlock_mark(struct tdb_context *tdb, TDB_DATA key)
 int tdb_chainlock_unmark(struct tdb_context *tdb, TDB_DATA key)
 {
 	tdb_trace_1rec(tdb, "tdb_chainlock_unmark", key);
-	return tdb_unlock(tdb, BUCKET(tdb->hash_fn(&key)), F_WRLCK | TDB_MARK_LOCK);
+	return _tdb_unlock(tdb, BUCKET(tdb->hash_fn(&key)), F_WRLCK, true);
 }
 
 int tdb_chainunlock(struct tdb_context *tdb, TDB_DATA key)
@@ -546,7 +639,7 @@ int tdb_lock_record(struct tdb_context *tdb, tdb_off_t off)
 	if (tdb->global_lock.count) {
 		return 0;
 	}
-	return off ? tdb->methods->tdb_brlock(tdb, off, F_RDLCK, F_SETLKW, 0, 1) : 0;
+	return off ? tdb->methods->brlock(tdb, F_RDLCK, off, 1, TDB_LOCK_WAIT) : 0;
 }
 
 /*
@@ -560,16 +653,12 @@ int tdb_write_lock_record(struct tdb_context *tdb, tdb_off_t off)
 	for (i = &tdb->travlocks; i; i = i->next)
 		if (i->off == off)
 			return -1;
-	return tdb->methods->tdb_brlock(tdb, off, F_WRLCK, F_SETLK, 1, 1);
+	return tdb->methods->brlock(tdb, F_WRLCK, off, 1, TDB_LOCK_NOWAIT|TDB_LOCK_PROBE);
 }
 
-/*
-  Note this is meant to be F_SETLK, *not* F_SETLKW, as it's not
-  an error to fail to get the lock here.
-*/
 int tdb_write_unlock_record(struct tdb_context *tdb, tdb_off_t off)
 {
-	return tdb->methods->tdb_brlock(tdb, off, F_UNLCK, F_SETLK, 0, 1);
+	return tdb->methods->brunlock(tdb, F_WRLCK, off, 1);
 }
 
 /* fcntl locks don't stack: avoid unlocking someone else's */
@@ -587,5 +676,5 @@ int tdb_unlock_record(struct tdb_context *tdb, tdb_off_t off)
 	for (i = &tdb->travlocks; i; i = i->next)
 		if (i->off == off)
 			count++;
-	return (count == 1 ? tdb->methods->tdb_brlock(tdb, off, F_UNLCK, F_SETLKW, 0, 1) : 0);
+	return (count == 1 ? tdb->methods->brunlock(tdb, F_RDLCK, off, 1) : 0);
 }
diff --git a/ccan/tdb/open.c b/ccan/tdb/open.c
index 0318530f..8b977686 100644
--- a/ccan/tdb/open.c
+++ b/ccan/tdb/open.c
@@ -226,7 +226,7 @@ struct tdb_context *tdb_open_ex(const char *name, int hash_size, int tdb_flags,
         fcntl(tdb->fd, F_SETFD, v | FD_CLOEXEC);
 
 	/* ensure there is only one process initialising at once */
-	if (tdb->methods->tdb_brlock(tdb, GLOBAL_LOCK, F_WRLCK, F_SETLKW, 0, 1) == -1) {
+	if (tdb->methods->brlock(tdb, F_WRLCK, GLOBAL_LOCK, 1, TDB_LOCK_WAIT) == -1) {
 		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_open_ex: failed to get global lock on %s: %s\n",
 			 name, strerror(errno)));
 		goto fail;	/* errno set by tdb_brlock */
@@ -235,7 +235,7 @@ struct tdb_context *tdb_open_ex(const char *name, int hash_size, int tdb_flags,
 	/* we need to zero database if we are the only one with it open */
 	if ((tdb_flags & TDB_CLEAR_IF_FIRST) &&
 	    (!tdb->read_only) &&
-	    (locked = (tdb->methods->tdb_brlock(tdb, ACTIVE_LOCK, F_WRLCK, F_SETLK, 0, 1) == 0))) {
+	    (locked = (tdb->methods->brlock(tdb, F_WRLCK, ACTIVE_LOCK, 1, TDB_LOCK_NOWAIT|TDB_LOCK_PROBE) == 0))) {
 		open_flags |= O_CREAT;
 		if (ftruncate(tdb->fd, 0) == -1) {
 			TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_open_ex: "
@@ -298,7 +298,7 @@ struct tdb_context *tdb_open_ex(const char *name, int hash_size, int tdb_flags,
 	tdb->inode = st.st_ino;
 	tdb_mmap(tdb);
 	if (locked) {
-		if (tdb->methods->tdb_brlock(tdb, ACTIVE_LOCK, F_UNLCK, F_SETLK, 0, 1) == -1) {
+		if (tdb->methods->brunlock(tdb, F_WRLCK, ACTIVE_LOCK, 1) == -1) {
 			TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_open_ex: "
 				 "failed to take ACTIVE_LOCK on %s: %s\n",
 				 name, strerror(errno)));
@@ -313,7 +313,7 @@ struct tdb_context *tdb_open_ex(const char *name, int hash_size, int tdb_flags,
 
 	if (tdb_flags & TDB_CLEAR_IF_FIRST) {
 		/* leave this lock in place to indicate it's in use */
-		if (tdb->methods->tdb_brlock(tdb, ACTIVE_LOCK, F_RDLCK, F_SETLKW, 0, 1) == -1)
+		if (tdb->methods->brlock(tdb, F_RDLCK, ACTIVE_LOCK, 1, TDB_LOCK_WAIT) == -1)
 			goto fail;
 	}
 
@@ -341,7 +341,7 @@ struct tdb_context *tdb_open_ex(const char *name, int hash_size, int tdb_flags,
 	/* Internal (memory-only) databases skip all the code above to
 	 * do with disk files, and resume here by releasing their
 	 * global lock and hooking into the active list. */
-	if (tdb->methods->tdb_brlock(tdb, GLOBAL_LOCK, F_UNLCK, F_SETLKW, 0, 1) == -1)
+	if (tdb->methods->brunlock(tdb, F_WRLCK, GLOBAL_LOCK, 1) == -1)
 		goto fail;
 	tdb->next = tdbs;
 	tdbs = tdb;
@@ -391,10 +391,10 @@ int tdb_close(struct tdb_context *tdb)
 	struct tdb_context **i;
 	int ret = 0;
 
-	tdb_trace(tdb, "tdb_close");
 	if (tdb->transaction) {
-		_tdb_transaction_cancel(tdb);
+		tdb_transaction_cancel(tdb);
 	}
+	tdb_trace(tdb, "tdb_close");
 
 	if (tdb->map_ptr) {
 		if (tdb->flags & TDB_INTERNAL)
@@ -468,7 +468,7 @@ int tdb_reopen(struct tdb_context *tdb)
 		goto fail;
 	}
 	if ((tdb->flags & TDB_CLEAR_IF_FIRST) && 
-	    (tdb->methods->tdb_brlock(tdb, ACTIVE_LOCK, F_RDLCK, F_SETLKW, 0, 1) == -1)) {
+	    (tdb->methods->brlock(tdb, F_RDLCK, ACTIVE_LOCK, 1, TDB_LOCK_WAIT) == -1)) {
 		TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_reopen: failed to obtain active lock\n"));
 		goto fail;
 	}
diff --git a/ccan/tdb/tdb.c b/ccan/tdb/tdb.c
index 0db9a358..d4341803 100644
--- a/ccan/tdb/tdb.c
+++ b/ccan/tdb/tdb.c
@@ -59,13 +59,14 @@ static void tdb_increment_seqnum(struct tdb_context *tdb)
 		return;
 	}
 
-	if (tdb_brlock(tdb, TDB_SEQNUM_OFS, F_WRLCK, F_SETLKW, 1, 1) != 0) {
+	if (tdb_brlock(tdb, F_WRLCK, TDB_SEQNUM_OFS, 1,
+		       TDB_LOCK_WAIT|TDB_LOCK_PROBE) != 0) {
 		return;
 	}
 
 	tdb_increment_seqnum_nonblock(tdb);
 
-	tdb_brlock(tdb, TDB_SEQNUM_OFS, F_UNLCK, F_SETLKW, 1, 1);
+	tdb_brunlock(tdb, F_WRLCK, TDB_SEQNUM_OFS, 1);
 }
 
 static int tdb_key_compare(TDB_DATA key, TDB_DATA data, void *private_data)
diff --git a/ccan/tdb/tdb_private.h b/ccan/tdb/tdb_private.h
index c1a9925f..ef85385c 100644
--- a/ccan/tdb/tdb_private.h
+++ b/ccan/tdb/tdb_private.h
@@ -182,6 +182,15 @@ struct tdb_traverse_lock {
 	int lock_rw;
 };
 
+enum tdb_lock_flags {
+	/* WAIT == F_SETLKW, NOWAIT == F_SETLK */
+	TDB_LOCK_NOWAIT = 0,
+	TDB_LOCK_WAIT = 1,
+	/* If set, don't log an error on failure. */
+	TDB_LOCK_PROBE = 2,
+	/* If set, don't actually lock at all. */
+	TDB_LOCK_MARK_ONLY = 4,
+};
 
 struct tdb_methods {
 	int (*tdb_read)(struct tdb_context *, tdb_off_t , void *, tdb_len_t , int );
@@ -189,7 +198,8 @@ struct tdb_methods {
 	void (*next_hash_chain)(struct tdb_context *, uint32_t *);
 	int (*tdb_oob)(struct tdb_context *, tdb_off_t , int );
 	int (*tdb_expand_file)(struct tdb_context *, tdb_off_t , tdb_off_t );
-	int (*tdb_brlock)(struct tdb_context *, tdb_off_t , int, int, int, size_t);
+	int (*brlock)(struct tdb_context *, int, tdb_off_t, size_t, enum tdb_lock_flags);
+	int (*brunlock)(struct tdb_context *, int, tdb_off_t, size_t);
 };
 
 struct tdb_context {
@@ -235,9 +245,13 @@ void tdb_mmap(struct tdb_context *tdb);
 int tdb_lock(struct tdb_context *tdb, int list, int ltype);
 int tdb_lock_nonblock(struct tdb_context *tdb, int list, int ltype);
 int tdb_unlock(struct tdb_context *tdb, int list, int ltype);
-int tdb_brlock(struct tdb_context *tdb, tdb_off_t offset, int rw_type, int lck_type, int probe, size_t len);
+int tdb_brlock(struct tdb_context *tdb,
+	       int rw_type, tdb_off_t offset, size_t len,
+	       enum tdb_lock_flags flags);
+int tdb_brunlock(struct tdb_context *tdb,
+		 int rw_type, tdb_off_t offset, size_t len);
 int tdb_transaction_lock(struct tdb_context *tdb, int ltype);
-int tdb_transaction_unlock(struct tdb_context *tdb);
+int tdb_transaction_unlock(struct tdb_context *tdb, int ltype);
 int tdb_brlock_upgrade(struct tdb_context *tdb, tdb_off_t offset, size_t len);
 int tdb_write_lock_record(struct tdb_context *tdb, tdb_off_t off);
 int tdb_write_unlock_record(struct tdb_context *tdb, tdb_off_t off);
@@ -250,7 +264,7 @@ int tdb_ofs_read(struct tdb_context *tdb, tdb_off_t offset, tdb_off_t *d);
 int tdb_ofs_write(struct tdb_context *tdb, tdb_off_t offset, tdb_off_t *d);
 int tdb_lock_record(struct tdb_context *tdb, tdb_off_t off);
 int tdb_unlock_record(struct tdb_context *tdb, tdb_off_t off);
-int _tdb_transaction_cancel(struct tdb_context *tdb);
+int _tdb_transaction_cancel(struct tdb_context *tdb, int ltype);
 int tdb_rec_read(struct tdb_context *tdb, tdb_off_t offset, struct list_struct *rec);
 int tdb_rec_write(struct tdb_context *tdb, tdb_off_t offset, struct list_struct *rec);
 int tdb_do_delete(struct tdb_context *tdb, tdb_off_t rec_ptr, struct list_struct *rec);
diff --git a/ccan/tdb/test/run-3G-file.c b/ccan/tdb/test/run-3G-file.c
index d19decc7..8b75f2b8 100644
--- a/ccan/tdb/test/run-3G-file.c
+++ b/ccan/tdb/test/run-3G-file.c
@@ -50,7 +50,8 @@ static const struct tdb_methods large_io_methods = {
 	tdb_next_hash_chain,
 	tdb_oob,
 	tdb_expand_file_sparse,
-	tdb_brlock
+	tdb_brlock,
+	tdb_brunlock
 };
 
 static int test_traverse(struct tdb_context *tdb, TDB_DATA key, TDB_DATA data,
diff --git a/ccan/tdb/transaction.c b/ccan/tdb/transaction.c
index 7e8ac34d..c2e4748a 100644
--- a/ccan/tdb/transaction.c
+++ b/ccan/tdb/transaction.c
@@ -411,8 +411,15 @@ static int transaction_expand_file(struct tdb_context *tdb, tdb_off_t size,
 /*
   brlock during a transaction - ignore them
 */
-static int transaction_brlock(struct tdb_context *tdb, tdb_off_t offset, 
-			      int rw_type, int lck_type, int probe, size_t len)
+static int transaction_brlock(struct tdb_context *tdb,
+			      int rw_type, tdb_off_t offset, size_t len,
+			      enum tdb_lock_flags flags)
+{
+	return 0;
+}
+
+static int transaction_brunlock(struct tdb_context *tdb,
+				int rw_type, tdb_off_t offset, size_t len)
 {
 	return 0;
 }
@@ -423,7 +430,8 @@ static const struct tdb_methods transaction_methods = {
 	transaction_next_hash_chain,
 	transaction_oob,
 	transaction_expand_file,
-	transaction_brlock
+	transaction_brlock,
+	transaction_brunlock
 };
 
 /*
@@ -455,7 +463,8 @@ static int transaction_sync(struct tdb_context *tdb, tdb_off_t offset, tdb_len_t
 	return 0;
 }
 
-int _tdb_transaction_cancel(struct tdb_context *tdb)
+/* ltype is F_WRLCK after prepare. */
+int _tdb_transaction_cancel(struct tdb_context *tdb, int ltype)
 {
 	int i, ret = 0;
 
@@ -494,15 +503,16 @@ int _tdb_transaction_cancel(struct tdb_context *tdb)
 
 	/* remove any global lock created during the transaction */
 	if (tdb->global_lock.count != 0) {
-		tdb_brlock(tdb, FREELIST_TOP, F_UNLCK, F_SETLKW, 0, 4*tdb->header.hash_size);
+		tdb_brunlock(tdb, tdb->global_lock.ltype,
+			     FREELIST_TOP, 4*tdb->header.hash_size);
 		tdb->global_lock.count = 0;
 	}
 
 	/* remove any locks created during the transaction */
 	if (tdb->num_locks != 0) {
 		for (i=0;i<tdb->num_lockrecs;i++) {
-			tdb_brlock(tdb,FREELIST_TOP+4*tdb->lockrecs[i].list,
-				   F_UNLCK,F_SETLKW, 0, 1);
+			tdb_brunlock(tdb, tdb->lockrecs[i].ltype,
+				     FREELIST_TOP+4*tdb->lockrecs[i].list, 1);
 		}
 		tdb->num_locks = 0;
 		tdb->num_lockrecs = 0;
@@ -512,8 +522,8 @@ int _tdb_transaction_cancel(struct tdb_context *tdb)
 	/* restore the normal io methods */
 	tdb->methods = tdb->transaction->io_methods;
 
-	tdb_brlock(tdb, FREELIST_TOP, F_UNLCK, F_SETLKW, 0, 0);
-	tdb_transaction_unlock(tdb);
+	tdb_brunlock(tdb, ltype, FREELIST_TOP, 0);
+	tdb_transaction_unlock(tdb, F_WRLCK);
 	SAFE_FREE(tdb->transaction->hash_heads);
 	SAFE_FREE(tdb->transaction);
 	
@@ -585,7 +595,7 @@ int tdb_transaction_start(struct tdb_context *tdb)
 	
 	/* get a read lock from the freelist to the end of file. This
 	   is upgraded to a write lock during the commit */
-	if (tdb_brlock(tdb, FREELIST_TOP, F_RDLCK, F_SETLKW, 0, 0) == -1) {
+	if (tdb_brlock(tdb, F_RDLCK, FREELIST_TOP, 0, TDB_LOCK_WAIT) == -1) {
 		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_start: failed to get hash locks\n"));
 		tdb->ecode = TDB_ERR_LOCK;
 		goto fail;
@@ -621,8 +631,8 @@ int tdb_transaction_start(struct tdb_context *tdb)
 	return 0;
 	
 fail:
-	tdb_brlock(tdb, FREELIST_TOP, F_UNLCK, F_SETLKW, 0, 0);
-	tdb_transaction_unlock(tdb);
+	tdb_brunlock(tdb, F_RDLCK, FREELIST_TOP, 0);
+	tdb_transaction_unlock(tdb, F_WRLCK);
 	SAFE_FREE(tdb->transaction->blocks);
 	SAFE_FREE(tdb->transaction->hash_heads);
 	SAFE_FREE(tdb->transaction);
@@ -634,9 +644,12 @@ fail:
   cancel the current transaction
 */
 int tdb_transaction_cancel(struct tdb_context *tdb)
-{	
+{
+	int ltype = F_RDLCK;
 	tdb_trace(tdb, "tdb_transaction_cancel");
-	return _tdb_transaction_cancel(tdb);
+	if (tdb->transaction && tdb->transaction->prepared)
+		ltype = F_WRLCK;
+	return _tdb_transaction_cancel(tdb, ltype);
 }
 
 /*
@@ -896,14 +909,14 @@ static int _tdb_transaction_prepare_commit(struct tdb_context *tdb)
 
 	if (tdb->transaction->prepared) {
 		tdb->ecode = TDB_ERR_EINVAL;
-		_tdb_transaction_cancel(tdb);
+		_tdb_transaction_cancel(tdb, F_WRLCK);
 		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_prepare_commit: transaction already prepared\n"));
 		return -1;
 	}
 
 	if (tdb->transaction->transaction_error) {
 		tdb->ecode = TDB_ERR_IO;
-		_tdb_transaction_cancel(tdb);
+		_tdb_transaction_cancel(tdb, F_RDLCK);
 		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_prepare_commit: transaction error pending\n"));
 		return -1;
 	}
@@ -931,7 +944,7 @@ static int _tdb_transaction_prepare_commit(struct tdb_context *tdb)
 	if (tdb->num_locks || tdb->global_lock.count) {
 		tdb->ecode = TDB_ERR_LOCK;
 		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_prepare_commit: locks pending on commit\n"));
-		_tdb_transaction_cancel(tdb);
+		_tdb_transaction_cancel(tdb, F_RDLCK);
 		return -1;
 	}
 
@@ -939,16 +952,16 @@ static int _tdb_transaction_prepare_commit(struct tdb_context *tdb)
 	if (tdb_brlock_upgrade(tdb, FREELIST_TOP, 0) == -1) {
 		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_prepare_commit: failed to upgrade hash locks\n"));
 		tdb->ecode = TDB_ERR_LOCK;
-		_tdb_transaction_cancel(tdb);
+		_tdb_transaction_cancel(tdb, F_RDLCK);
 		return -1;
 	}
 
 	/* get the global lock - this prevents new users attaching to the database
 	   during the commit */
-	if (tdb_brlock(tdb, GLOBAL_LOCK, F_WRLCK, F_SETLKW, 0, 1) == -1) {
+	if (tdb_brlock(tdb, F_WRLCK, GLOBAL_LOCK, 1, TDB_LOCK_WAIT) == -1) {
 		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_prepare_commit: failed to get global lock\n"));
 		tdb->ecode = TDB_ERR_LOCK;
-		_tdb_transaction_cancel(tdb);
+		_tdb_transaction_cancel(tdb, F_WRLCK);
 		return -1;
 	}
 
@@ -956,8 +969,8 @@ static int _tdb_transaction_prepare_commit(struct tdb_context *tdb)
 		/* write the recovery data to the end of the file */
 		if (transaction_setup_recovery(tdb, &tdb->transaction->magic_offset) == -1) {
 			TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_prepare_commit: failed to setup recovery data\n"));
-			tdb_brlock(tdb, GLOBAL_LOCK, F_UNLCK, F_SETLKW, 0, 1);
-			_tdb_transaction_cancel(tdb);
+			tdb_brunlock(tdb, F_WRLCK, GLOBAL_LOCK, 0);
+			_tdb_transaction_cancel(tdb, F_WRLCK);
 			return -1;
 		}
 	}
@@ -971,8 +984,8 @@ static int _tdb_transaction_prepare_commit(struct tdb_context *tdb)
 					     tdb->transaction->old_map_size) == -1) {
 			tdb->ecode = TDB_ERR_IO;
 			TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_prepare_commit: expansion failed\n"));
-			tdb_brlock(tdb, GLOBAL_LOCK, F_UNLCK, F_SETLKW, 0, 1);
-			_tdb_transaction_cancel(tdb);
+			tdb_brunlock(tdb, F_WRLCK, GLOBAL_LOCK, 0);
+			_tdb_transaction_cancel(tdb, F_WRLCK);
 			return -1;
 		}
 		tdb->map_size = tdb->transaction->old_map_size;
@@ -1030,7 +1043,7 @@ int tdb_transaction_commit(struct tdb_context *tdb)
 
 	/* check for a null transaction */
 	if (tdb->transaction->blocks == NULL) {
-		_tdb_transaction_cancel(tdb);
+		_tdb_transaction_cancel(tdb, F_RDLCK);
 		return 0;
 	}
 
@@ -1066,8 +1079,8 @@ int tdb_transaction_commit(struct tdb_context *tdb)
 			tdb->methods = methods;
 			tdb_transaction_recover(tdb); 
 
-			_tdb_transaction_cancel(tdb);
-			tdb_brlock(tdb, GLOBAL_LOCK, F_UNLCK, F_SETLKW, 0, 1);
+			_tdb_transaction_cancel(tdb, F_WRLCK);
+			tdb_brunlock(tdb, F_WRLCK, GLOBAL_LOCK, 0);
 
 			TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_commit: write failed\n"));
 			return -1;
@@ -1083,7 +1096,7 @@ int tdb_transaction_commit(struct tdb_context *tdb)
 		return -1;
 	}
 
-	tdb_brlock(tdb, GLOBAL_LOCK, F_UNLCK, F_SETLKW, 0, 1);
+	tdb_brunlock(tdb, F_WRLCK, GLOBAL_LOCK, 1);
 
 	/*
 	  TODO: maybe write to some dummy hdr field, or write to magic
@@ -1104,7 +1117,7 @@ int tdb_transaction_commit(struct tdb_context *tdb)
 
 	/* use a transaction cancel to free memory and remove the
 	   transaction locks */
-	_tdb_transaction_cancel(tdb);
+	_tdb_transaction_cancel(tdb, F_WRLCK);
 
 	if (need_repack) {
 		return tdb_repack(tdb);
diff --git a/ccan/tdb/traverse.c b/ccan/tdb/traverse.c
index 953edcf4..1ca88d71 100644
--- a/ccan/tdb/traverse.c
+++ b/ccan/tdb/traverse.c
@@ -229,7 +229,7 @@ int tdb_traverse_read(struct tdb_context *tdb,
 	ret = _tdb_traverse(tdb, fn, private_data, &tl);
 	tdb->traverse_read--;
 
-	tdb_transaction_unlock(tdb);
+	tdb_transaction_unlock(tdb, F_RDLCK);
 
 	return ret;
 }
@@ -260,7 +260,7 @@ int tdb_traverse(struct tdb_context *tdb,
 	ret = _tdb_traverse(tdb, fn, private_data, &tl);
 	tdb->traverse_write--;
 
-	tdb_transaction_unlock(tdb);
+	tdb_transaction_unlock(tdb, F_WRLCK);
 
 	return ret;
 }