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Commit 2beb6614 authored by Marc Eshel's avatar Marc Eshel Committed by J. Bruce Fields
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locks: add fl_grant callback for asynchronous lock return 



Acquiring a lock on a cluster filesystem may require communication with
remote hosts, and to avoid blocking lockd or nfsd threads during such
communication, we allow the results to be returned asynchronously.

When a ->lock() call needs to block, the file system will return
-EINPROGRESS, and then later return the results with a call to the
routine in the fl_grant field of the lock_manager_operations struct.

This differs from the case when ->lock returns -EAGAIN to a blocking
lock request; in that case, the filesystem calls fl_notify when the lock
is granted, and the caller retries the original lock.  So while
fl_notify is merely a hint to the caller that it should retry, fl_grant
actually communicates the final result of the lock operation (with the
lock already acquired in the succesful case).

Therefore fl_grant takes a lock, a status and, for the test lock case, a
conflicting lock.  We also allow fl_grant to return an error to the
filesystem, to handle the case where the fl_grant requests arrives after
the lock manager has already given up waiting for it.

Signed-off-by: default avatarMarc Eshel <eshel@almaden.ibm.com>
Signed-off-by: default avatarJ. Bruce Fields <bfields@citi.umich.edu>
parent fd85b817

fs/locks.c

+19 −0
Original line number Diff line number Diff line
@@ -1698,6 +1698,25 @@ out: 
 * If the filesystem defines a private ->lock() method, then @conf will

 * be left unchanged; so a caller that cares should initialize it to

 * some acceptable default.

 *

 * 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)

 * fl_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 -EINPROGRESS, and call ->fl_grant() when the lock

 * request completes.

 * If the request is for non-blocking lock the file system should return

 * -EINPROGRESS 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

 * nonzero return code and the file system should release the lock. The file

 * system is also responsible to keep a corresponding posix lock when it

 * grants a lock so the VFS can find out which locks are locally held and do

 * the correct lock cleanup when required.

 * The underlying filesystem must not drop the kernel lock or call

 * ->fl_grant() before returning to the caller with a -EINPROGRESS

 * return code.

 */

int vfs_lock_file(struct file *filp, unsigned int cmd, struct file_lock *fl, struct file_lock *conf)

{

include/linux/fs.h

+1 −0
Original line number Diff line number Diff line
@@ -785,6 +785,7 @@ struct file_lock_operations { 
struct lock_manager_operations {

	int (*fl_compare_owner)(struct file_lock *, struct file_lock *);

	void (*fl_notify)(struct file_lock *);	/* unblock callback */

	int (*fl_grant)(struct file_lock *, struct file_lock *, int);

	void (*fl_copy_lock)(struct file_lock *, struct file_lock *);

	void (*fl_release_private)(struct file_lock *);

	void (*fl_break)(struct file_lock *);