tdb2: allow nesting of read locks on top of write locks.

If we have a write lock and ask for a read lock, that's OK, but not the
other way around.  tdb_nest_lock() allowed both, tdb_allrecord_lock() allowed
neither.

diff --git a/ccan/tdb2/lock.c b/ccan/tdb2/lock.c
index 5d13a23aaec89f17e731ffc71415fb43ceb7bafb..60ed46379aa7b6960d51e5778c907945614b7c0f 100644 (file)
--- a/ccan/tdb2/lock.c
+++ b/ccan/tdb2/lock.c
@@ -270,10 +270,14 @@ static int tdb_nest_lock(struct tdb_context *tdb, tdb_off_t offset, int ltype,
 
        new_lck = find_nestlock(tdb, offset);
        if (new_lck) {
-               /*
-                * Just increment the in-memory struct, posix locks
-                * don't stack.
-                */
+               if (new_lck->ltype == F_RDLCK && ltype == F_WRLCK) {
+                       tdb->ecode = TDB_ERR_LOCK;
+                       tdb->log(tdb, TDB_DEBUG_FATAL, tdb->log_priv,
+                                "tdb_nest_lock: offset %llu has read lock\n",
+                                (long long)offset);
+                       return -1;
+               }
+               /* Just increment the struct, posix locks don't stack. */
                new_lck->count++;
                return 0;
        }
@@ -454,7 +458,8 @@ int tdb_allrecord_lock(struct tdb_context *tdb, int ltype,
                return -1;
        }
 
-       if (tdb->allrecord_lock.count && tdb->allrecord_lock.ltype == ltype) {
+       if (tdb->allrecord_lock.count
+           && (ltype == F_RDLCK || tdb->allrecord_lock.ltype == F_WRLCK)) {
                tdb->allrecord_lock.count++;
                return 0;
        }