s3: locking: Convert on the wire behavior of POSIX (UNIX extensions) locks from process-associated locks to open file description locks.

This means locks are associated with the SMB handle
they were created on, not the inode. In all other ways
they behave like UNIX extensions fcntl (process-associated)
locks. Torture test to follow.

When a handle is closed all locks attached to that handle
are closed, not all locks on the underlying inode. In
this respect they now behave like Windows locks.

The key to this in the UNIX extensions locking codepath is modifying
the reference count only when a new locking context is seen
on any lock request, and decrementing the reference count
when the last instance of a locking context is seen on any
unlock request. For SMB2+ the persistent part of a file handle
is used as the locking context so this behavior becomes
natural.

This is a behavior change but after consultation with
Jeff Layton and Steve French the only client that implements
UNIX extensions POSIX locks - the cifsfs client - already
expects these locks to behave like open file description
(ofd) locks. With our previous behavior Linux ofd-locks
fail against smbd.

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Jeff Layton <jlayton@samba.org>

source3/locking/posix.c

@@ -1179,6 +1179,86 @@ bool release_posix_lock_windows_flavour(files_struct *fsp,
  the underlying system POSIX locks.
 ****************************************************************************/
 
+/****************************************************************************
+ We only increment the lock ref count when we see a POSIX lock on a context
+ that doesn't already have them.
+****************************************************************************/
+
+static void increment_posix_lock_count(const files_struct *fsp,
+					uint64_t smblctx)
+{
+	NTSTATUS status;
+	TDB_DATA ctx_key;
+	TDB_DATA val = { 0 };
+
+	ctx_key.dptr = (uint8_t *)&smblctx;
+	ctx_key.dsize = sizeof(smblctx);
+
+	/*
+	 * Don't increment if we already have any POSIX flavor
+	 * locks on this context.
+	 */
+	if (dbwrap_exists(posix_pending_close_db, ctx_key)) {
+		return;
+	}
+
+	/* Remember that we have POSIX flavor locks on this context. */
+	status = dbwrap_store(posix_pending_close_db, ctx_key, val, 0);
+	SMB_ASSERT(NT_STATUS_IS_OK(status));
+
+	increment_lock_ref_count(fsp);
+
+	DEBUG(10,("posix_locks set for file %s\n",
+		fsp_str_dbg(fsp)));
+}
+
+static void decrement_posix_lock_count(const files_struct *fsp, uint64_t smblctx)
+{
+	NTSTATUS status;
+	TDB_DATA ctx_key;
+
+	ctx_key.dptr = (uint8_t *)&smblctx;
+	ctx_key.dsize = sizeof(smblctx);
+
+	status = dbwrap_delete(posix_pending_close_db, ctx_key);
+	SMB_ASSERT(NT_STATUS_IS_OK(status));
+
+	decrement_lock_ref_count(fsp);
+
+	DEBUG(10,("posix_locks deleted for file %s\n",
+		fsp_str_dbg(fsp)));
+}
+
+/****************************************************************************
+ Return true if any locks exist on the given lock context.
+****************************************************************************/
+
+static bool locks_exist_on_context(const struct lock_struct *plocks,
+				int num_locks,
+				const struct lock_context *lock_ctx)
+{
+	int i;
+
+	for (i=0; i < num_locks; i++) {
+		const struct lock_struct *lock = &plocks[i];
+
+		/* Ignore all but read/write locks. */
+		if (lock->lock_type != READ_LOCK && lock->lock_type != WRITE_LOCK) {
+			continue;
+		}
+
+		/* Ignore locks not owned by this process. */
+		if (!serverid_equal(&lock->context.pid, &lock_ctx->pid)) {
+			continue;
+		}
+
+		if (lock_ctx->smblctx == lock->context.smblctx) {
+			return true;
+		}
+	}
+	return false;
+}
+
 /****************************************************************************
  POSIX function to acquire a lock. Returns True if the
  lock could be granted, False if not.
@@ -1210,6 +1290,7 @@ bool set_posix_lock_posix_flavour(files_struct *fsp,
 	 */
 
 	if(!posix_lock_in_range(&offset, &count, u_offset, u_count)) {
+		increment_posix_lock_count(fsp, lock_ctx->smblctx);
 		return True;
 	}
 
@@ -1219,6 +1300,7 @@ bool set_posix_lock_posix_flavour(files_struct *fsp,
 			posix_lock_type_name(posix_lock_type), (intmax_t)offset, (intmax_t)count, strerror(errno) ));
 		return False;
 	}
+	increment_posix_lock_count(fsp, lock_ctx->smblctx);
 	return True;
 }
 
@@ -1255,6 +1337,9 @@ bool release_posix_lock_posix_flavour(files_struct *fsp,
 	 */
 
 	if(!posix_lock_in_range(&offset, &count, u_offset, u_count)) {
+		if (!locks_exist_on_context(plocks, num_locks, lock_ctx)) {
+			decrement_posix_lock_count(fsp, lock_ctx->smblctx);
+		}
 		return True;
 	}
 
@@ -1308,6 +1393,9 @@ bool release_posix_lock_posix_flavour(files_struct *fsp,
 		}
 	}
 
+	if (!locks_exist_on_context(plocks, num_locks, lock_ctx)) {
+		decrement_posix_lock_count(fsp, lock_ctx->smblctx);
+	}
 	talloc_destroy(ul_ctx);
 	return ret;
 }