Re: [PATCH] Add support for flock over a cifs mount.

[Sachin Prabhu <sprabhu-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On Tue, 2011-11-08 at 23:08 +0400, Pavel Shilovsky wrote:

> Let's predict the following situation:
> 
> 1) f1 = open(filename)
> 2) f2 = open(filename) # the same process
> 3) f1.lock(0, 1) # lock file from 0 to 1
> 4) f2.lock(1, 2) # lock file from 1 to 2
> 5) f1.unlock(0, 2)
> 
> it unlocks both locks (3) and (4) from the VFS cache but unlock only
> (3) lock from CIFS-lock cache and server side (see cifs_unlock_range -
> it unlocks only locks held by the same fd, not the same process) - the
> lock (4) is still there.
> 
> 6) f2.unlock(1, 2)
> 
> it appears into if (unlock) {}, fails on FL_EXISTS with -ENOENT and
> goto out. The result we can't unlock the existing lock - the problem!
> 

Hello Pavel,

Thanks for your reply.

In my opinion this behaviour is wrong. The application running on the
Linux box will expect the locking behaviour to follow Posix locking
semantics. The current behaviour will break these applications which
expect the system to work in this manner.

After step 5, the client should unlock the whole range and send 2
separate unlock requests to the file server using 2 different netfids if
required.


Sachin Prabhu