Re: [PATCH] lockd: unlock when client rejects GRANTED_MSG

["J. Bruce Fields" <bfields@fieldses.org>]

On Sun, Jul 01, 2007 at 04:38:01PM +0200, Frank van Maarseveen wrote:
> 
> When lockd grants a blocked lock request after a while then the client
> response on it should not be ignored: When the client rejects GRANTED_MSG
> with GRANTED_RES NLM_LCK_DENIED then lockd on the server must release
> the POSIX lock.

There's not really any way to "remove" a posix lock.  All you can do is
issue an unlock, which isn't quite the same--for example, consider the
case when the granted lock was a read lock downgrading a previously
write-locked region.  Or perhaps it was locking a region only some of
whose bytes where previously locked.

I have some bit-rotting patches that define a new "provisional" lock
type that is like a posix lock except that it isn't combined with other
existing locks--such a lock has the advantage that it really can be
completely undone.  You can then break up the lock-applying process into
two steps:

	1. first apply a "provisional" lock (marked with an FL_BLOCK
	   lock type in my code), then
	2. when whoever originally requested the lock requests it,
	   convert the provisional lock until a real posix lock,
	   combining it with other locks as necessary.

So we could handle your case by delaying step number 2 until we get an
affirmative response to the grant.  I don't think my previous attempt
actually considered that case; I was mainly interested in NFSv4.  The
code's at

	git://linux-nfs.org/~bfields/linux.git	fair-queueing

(see the next-to-latest patch on that branch).

But I don't know how much trouble it's worth going to to get this right;
the NLM protocol is inherently racy.  Is this something you saw in real
life?  What was the client, and why did it refuse the grant?

--b.

-------------------------------------------------------------------------
This SF.net email is sponsored by DB2 Express
Download DB2 Express C - the FREE version of DB2 express and take
control of your XML. No limits. Just data. Click to get it now.
http://sourceforge.net/powerbar/db2/
_______________________________________________
NFS maillist  -  NFS@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/nfs