From: Andrew Tridgell <tridge@samba.org>
Date: Sat, 5 May 2007 07:14:33 +0000 (+1000)
Subject: added tdb_chainlock_mark() call, which can be used to mark a chain locked without... 
X-Git-Tag: tevent-0.9.20~348^2~2775
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=d903e9542d6e04f757d523774098807259e83561;p=thirdparty%2Fsamba.git

added tdb_chainlock_mark() call, which can be used to mark a chain locked without actually locking it. This will be used to guarantee forward progress in the ctdb non-blocking lockwait code
(This used to be ctdb commit 2af98c3418496b39106c7282f550049ec8239657)
---

diff --git a/ctdb/lib/tdb/common/lock.c b/ctdb/lib/tdb/common/lock.c
index 14ccbe39765..140d17818c4 100644
--- a/ctdb/lib/tdb/common/lock.c
+++ b/ctdb/lib/tdb/common/lock.c
@@ -28,6 +28,8 @@
 
 #include "tdb_private.h"
 
+#define TDB_MARK_LOCK 0x80000000
+
 /* a byte range locking function - return 0 on success
    this functions locks/unlocks 1 byte at the specified offset.
 
@@ -109,6 +111,9 @@ static int _tdb_lock(struct tdb_context *tdb, int list, int ltype, int op)
 {
 	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 && 
@@ -158,7 +163,8 @@ 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 (tdb->methods->tdb_brlock(tdb,FREELIST_TOP+4*list,ltype, op,
+	if (!mark_lock &&
+	    tdb->methods->tdb_brlock(tdb,FREELIST_TOP+4*list, ltype, op,
 				     0, 1)) {
 		return -1;
 	}
@@ -200,6 +206,9 @@ int tdb_unlock(struct tdb_context *tdb, int list, int ltype)
 	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 && 
@@ -244,8 +253,12 @@ int tdb_unlock(struct tdb_context *tdb, int list, int ltype)
 	 * anyway.
 	 */
 
-	ret = tdb->methods->tdb_brlock(tdb, FREELIST_TOP+4*list, F_UNLCK,
-				       F_SETLKW, 0, 1);
+	if (mark_lock) {
+		ret = 0;
+	} else {
+		ret = tdb->methods->tdb_brlock(tdb, FREELIST_TOP+4*list, F_UNLCK,
+					       F_SETLKW, 0, 1);
+	}
 	tdb->num_locks--;
 
 	/*
@@ -376,6 +389,18 @@ int tdb_chainlock_nonblock(struct tdb_context *tdb, TDB_DATA key)
 	return tdb_lock_nonblock(tdb, BUCKET(tdb->hash_fn(&key)), F_WRLCK);
 }
 
+/* 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)
+{
+	return tdb_lock(tdb, BUCKET(tdb->hash_fn(&key)), F_WRLCK | TDB_MARK_LOCK);
+}
+
+/* unmark a chain as locked without actually locking it. Warning! use with great caution! */
+int tdb_chainlock_unmark(struct tdb_context *tdb, TDB_DATA key)
+{
+	return tdb_unlock(tdb, BUCKET(tdb->hash_fn(&key)), F_WRLCK | TDB_MARK_LOCK);
+}
+
 int tdb_chainunlock(struct tdb_context *tdb, TDB_DATA key)
 {
 	return tdb_unlock(tdb, BUCKET(tdb->hash_fn(&key)), F_WRLCK);
diff --git a/ctdb/lib/tdb/include/tdb.h b/ctdb/lib/tdb/include/tdb.h
index b3f6a840b94..36fc0b405a6 100644
--- a/ctdb/lib/tdb/include/tdb.h
+++ b/ctdb/lib/tdb/include/tdb.h
@@ -140,6 +140,8 @@ int tdb_chainlock_nonblock(struct tdb_context *tdb, TDB_DATA key);
 int tdb_chainunlock(struct tdb_context *tdb, TDB_DATA key);
 int tdb_chainlock_read(struct tdb_context *tdb, TDB_DATA key);
 int tdb_chainunlock_read(struct tdb_context *tdb, TDB_DATA key);
+int tdb_chainlock_mark(struct tdb_context *tdb, TDB_DATA key);
+int tdb_chainlock_unmark(struct tdb_context *tdb, TDB_DATA key);
 
 /* Debug functions. Not used in production. */
 void tdb_dump_all(struct tdb_context *tdb);