lockd: introduce safe async lock op

This patch reverts mostly commit 40595cdc93ed ("nfs: block notification
on fs with its own ->lock") and introduces an EXPORT_OP_ASYNC_LOCK
export flag to signal that the "own ->lock" implementation supports
async lock requests. The only main user is DLM that is used by GFS2 and
OCFS2 filesystem. Those implement their own lock() implementation and
return FILE_LOCK_DEFERRED as return value. Since commit 40595cdc93ed
("nfs: block notification on fs with its own ->lock") the DLM
implementation were never updated. This patch should prepare for DLM
to set the EXPORT_OP_ASYNC_LOCK export flag and update the DLM
plock implementation regarding to it.

Acked-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/Documentation/filesystems/nfs/exporting.rst b/Documentation/filesystems/nfs/exporting.rst
index 4b30daee399a..198d805d611c 100644
--- a/Documentation/filesystems/nfs/exporting.rst
+++ b/Documentation/filesystems/nfs/exporting.rst
@@ -241,3 +241,10 @@ following flags are defined:
     all of an inode's dirty data on last close. Exports that behave this
     way should set EXPORT_OP_FLUSH_ON_CLOSE so that NFSD knows to skip
     waiting for writeback when closing such files.
+
+  EXPORT_OP_ASYNC_LOCK - Indicates a capable filesystem to do async lock
+    requests from lockd. Only set EXPORT_OP_ASYNC_LOCK if the filesystem has
+    it's own ->lock() functionality as core posix_lock_file() implementation
+    has no async lock request handling yet. For more information about how to
+    indicate an async lock request from a ->lock() file_operations struct, see
+    fs/locks.c and comment for the function vfs_lock_file().