Re: [PATCH 4/7] lockd: add doc to enable EXPORT_OP_SAFE_ASYNC_LOCK

[Jeff Layton <jlayton@kernel.org>]

On Wed, 2023-08-23 at 17:33 -0400, Alexander Aring wrote:
> This patch adds a note to enable EXPORT_OP_SAFE_ASYNC_LOCK for
> asynchronous lock request handling.
> 
> Signed-off-by: Alexander Aring <aahringo@redhat.com>
> ---
>  fs/locks.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/locks.c b/fs/locks.c
> index df8b26a42524..edee02d1ca93 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -2255,11 +2255,13 @@ int fcntl_getlk(struct file *filp, unsigned int cmd, struct flock *flock)
>   * To avoid blocking kernel daemons, such as lockd, that need to acquire POSIX
>   * locks, the ->lock() interface may return asynchronously, before the lock has
>   * been granted or denied by the underlying filesystem, if (and only if)
> - * lm_grant is set. Callers expecting ->lock() to return asynchronously
> - * will only use F_SETLK, not F_SETLKW; they will set FL_SLEEP if (and only if)
> - * the request is for a blocking lock. When ->lock() does return asynchronously,
> - * it must return FILE_LOCK_DEFERRED, and call ->lm_grant() when the lock
> - * request completes.
> + * lm_grant is set. Additionally EXPORT_OP_SAFE_ASYNC_LOCK in export_operations
> + * flags need to be set.
> + *
> + * Callers expecting ->lock() to return asynchronously will only use F_SETLK,
> + * not F_SETLKW; they will set FL_SLEEP if (and only if) the request is for a
> + * blocking lock. When ->lock() does return asynchronously, it must return
> + * FILE_LOCK_DEFERRED, and call ->lm_grant() when the lock request completes.
>   * If the request is for non-blocking lock the file system should return
>   * FILE_LOCK_DEFERRED then try to get the lock and call the callback routine
>   * with the result. If the request timed out the callback routine will return a

Reviewed-by: Jeff Layton <jlayton@kernel.org>