source3/lib/util_tdb.c: operation timeout support for TDB2.

TDB2 doesn't have (the racy) signal pointer; the new method is to
override the locking callbacks and do the timeout internally.

The technique here is to invalidate the struct flock when the timeout
occurs, so it works even if it happens before we enter the fcntl() call.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 96 insertions, 0 deletions

diff --git a/source3/lib/util_tdb.c b/source3/lib/util_tdb.c
index 4756fd84ef..ade46bf18e 100644
--- a/source3/lib/util_tdb.c
+++ b/source3/lib/util_tdb.c
@@ -28,6 +28,101 @@
 #undef calloc
 #undef strdup
 
+#ifdef BUILD_TDB2
+static struct flock flock_struct;
+
+/* Return a value which is none of v1, v2 or v3. */
+static inline short int invalid_value(short int v1, short int v2, short int v3)
+{
+	short int try = (v1+v2+v3)^((v1+v2+v3) << 16);
+	while (try == v1 || try == v2 || try == v3)
+		try++;
+	return try;
+}
+
+/* We invalidate in as many ways as we can, so the OS rejects it */
+static void invalidate_flock_struct(int signum)
+{
+	flock_struct.l_type = invalid_value(F_RDLCK, F_WRLCK, F_UNLCK);
+	flock_struct.l_whence = invalid_value(SEEK_SET, SEEK_CUR, SEEK_END);
+	flock_struct.l_start = -1;
+	/* A large negative. */
+	flock_struct.l_len = (((off_t)1 << (sizeof(off_t)*CHAR_BIT - 1)) + 1);
+}
+
+static int timeout_lock(int fd, int rw, off_t off, off_t len, bool waitflag,
+			void *_timeout)
+{
+	int ret, saved_errno;
+	unsigned int timeout = *(unsigned int *)_timeout;
+
+	flock_struct.l_type = rw;
+	flock_struct.l_whence = SEEK_SET;
+	flock_struct.l_start = off;
+	flock_struct.l_len = len;
+
+	CatchSignal(SIGALRM, invalidate_flock_struct);
+	alarm(timeout);
+
+	for (;;) {
+		if (waitflag)
+			ret = fcntl(fd, F_SETLKW, &flock_struct);
+		else
+			ret = fcntl(fd, F_SETLK, &flock_struct);
+
+		if (ret == 0)
+			break;
+
+		/* Not signalled?  Something else went wrong. */
+		if (flock_struct.l_len == len) {
+			if (errno == EAGAIN || errno == EINTR)
+				continue;
+			saved_errno = errno;
+			break;
+		} else {
+			saved_errno = EINTR;
+			break;
+		}
+	}
+
+	alarm(0);
+	errno = saved_errno;
+	return ret;
+}
+
+static int tdb_chainlock_with_timeout_internal(struct tdb_context *tdb,
+					       TDB_DATA key,
+					       unsigned int timeout,
+					       int rw_type)
+{
+	union tdb_attribute locking;
+	enum TDB_ERROR ecode;
+
+	if (timeout) {
+		locking.base.attr = TDB_ATTRIBUTE_FLOCK;
+		ecode = tdb_get_attribute(tdb, &locking);
+		if (ecode != TDB_SUCCESS)
+			return ecode;
+
+		/* Replace locking function with our own. */
+		locking.flock.data = &timeout;
+		locking.flock.lock = timeout_lock;
+
+		ecode = tdb_set_attribute(tdb, &locking);
+		if (ecode != TDB_SUCCESS)
+			return ecode;
+	}
+	if (rw_type == F_RDLCK)
+		ecode = tdb_chainlock_read(tdb, key);
+	else
+		ecode = tdb_chainlock(tdb, key);
+
+	if (timeout) {
+		tdb_unset_attribute(tdb, TDB_ATTRIBUTE_FLOCK);
+	}
+	return ecode == TDB_SUCCESS ? 0 : -1;
+}
+#else
 /* these are little tdb utility functions that are meant to make
    dealing with a tdb database a little less cumbersome in Samba */
 
@@ -80,6 +175,7 @@ static int tdb_chainlock_with_timeout_internal( TDB_CONTEXT *tdb, TDB_DATA key,
 
 	return ret == 0 ? 0 : -1;
 }
+#endif /* TDB1 */
 
 /****************************************************************************
  Write lock a chain. Return non-zero if timeout or lock failed.