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lockd: add doc to enable EXPORT_OP_ASYNC_LOCK

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This patch adds a note to enable EXPORT_OP_ASYNC_LOCK for
asynchronous lock request handling.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
This commit is contained in:
Alexander Aring 2023-09-12 17:53:21 -04:00 committed by Chuck Lever
parent afb13302aa
commit e70da17633
1 changed files with 7 additions and 5 deletions
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12
fs/locks.c
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@ -2264,11 +2264,13 @@ out:
* 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_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