[Gluster-devel] mandatory lock

[Raghavendra G]

On Thu, Jan 8, 2015 at 9:37 PM, Anand Avati <avati at gluster.org> wrote:

> Note that the mandatory locks available in the locks translator is just
> the mandatory extensions for posix locks - at least one of the apps must be
> using locks to begin with.


Linux mandatory locking definition seems to convey exactly the above
meaning [1].

<extract>

4. Semantics
------------

1. Mandatory locks can only be applied via the fcntl()/lockf() locking
   interface - in other words the System V/POSIX interface. BSD style
   locks using flock() never result in a mandatory lock.

</extract>

[1]
https://www.kernel.org/doc/Documentation/filesystems/mandatory-locking.txt

What Harmeet is asking for is something different - automatic exclusive
> access to edit files. i.e, if one app has opened a file for editing, other
> apps which attempt an open must either fail (EBUSY) or block till the first
> app closes. We need to treat open(O_RDONLY) as a read lock and
> open(O_RDWR|O_WRONLY) as a write lock request (essentially an auto applied
> oplock). This is something gluster does not yet have.
>
> Thanks
>
> On Thu Jan 08 2015 at 2:49:29 AM Raghavendra Gowdappa <rgowdapp at redhat.com>
> wrote:
>
>>
>>
>> ----- Original Message -----
>> > From: "Raghavendra Gowdappa" <rgowdapp at redhat.com>
>> > To: "Harmeet Kalsi" <kharmeet at hotmail.com>
>> > Cc: "Gluster-devel at gluster.org" <gluster-devel at gluster.org>
>> > Sent: Thursday, January 8, 2015 4:12:44 PM
>> > Subject: Re: [Gluster-devel] mandatory lock
>> >
>> >
>> >
>> > ----- Original Message -----
>> > > From: "Harmeet Kalsi" <kharmeet at hotmail.com>
>> > > To: "Gluster-devel at gluster.org" <gluster-devel at gluster.org>
>> > > Sent: Wednesday, January 7, 2015 5:55:43 PM
>> > > Subject: [Gluster-devel] mandatory lock
>> > >
>> > > Dear All.
>> > > Would it be possible for someone to guide me in the right direction to
>> > > enable
>> > > the mandatory lock on a volume please.
>> > > At the moment two clients can edit the same file at the same time
>> which is
>> > > causing issues.
>> >
>> > I see code related to mandatory locking in posix-locks xlator
>> (pl_writev,
>> > pl_truncate etc). To enable it you've to set "option mandatory-locks
>> yes" in
>> > posix-locks xlator loaded on bricks
>> > (/var/lib/glusterd/vols/<volname>/*.vol). We've no way to set this
>> option
>> > through gluster cli. Also, I am not sure to what extent this feature is
>> > tested/used till now. You can try it out and please let us know whether
>> it
>> > worked for you :).
>>
>> If mandatory locking doesn't work for you, can you modify your
>> application to use advisory locking, since advisory locking is tested well
>> and being used for long time?
>>
>> >
>> > > Many thanks in advance
>> > > Kind Regards
>> > >
>> > > _______________________________________________
>> > > Gluster-devel mailing list
>> > > Gluster-devel at gluster.org
>> > > http://www.gluster.org/mailman/listinfo/gluster-devel
>> > >
>> > _______________________________________________
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>> >
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>
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>


-- 
Raghavendra G
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