Re: [Fwd: [PATCH] Fix race in xfs_write() between direct and buffered I/O with DMAPI]

[Lachlan McIlroy <lachlan@xxxxxxx>]

Niv Sardi wrote:
> Lachlan McIlroy <lachlan@xxxxxxx> writes:
>
> > Christoph Hellwig wrote:
> >
> > > On Tue, Dec 23, 2008 at 11:40:24AM +1100, Lachlan McIlroy wrote:
> > > > Christoph Hellwig wrote:
> > > > > Do you need more input on this one?
> > > > Actually I just might.  Based on your last reponse I wasn't sure if
> > > > you wanted me to make further changes.
> > > Well, my reponse was that I think we could do it more effecient, but the
> > > patch still looks correct to me.
> > Okay great.  I'll check it in and we can improve it later when I understand
> > what you meant!
> >
> > > > Then I got side-tracked wondering
> > > > why we even have the 'goto retry' in the dmapi post event - why retry the
> > > > write if we get ENOSPC when we don't if dmapi is not enabled?  Could the
> > > > write get stuck in an infinite loop?
> > > We only retry on ENOSPC if the dmapi nospace even is enabled, or am I
> > > missing something?
> > I don't think you're missing anything here.  I don't understand how the
> > DMAPI stuff works but I imagined the event was there to indicate that the
> > write failed but what I don't understand is why that justifies a retry.
> > Is there something about DMAPI that needs the write to succeed?
> yes
>
> http://www.opengroup.org/onlinepubs/9657099/chap3.htm#tagcjh_04_02_04
Oh no, not the DMAPI spec - I don't want to go there!  Sounds like the
XFS_SEND_NAMESP() event can choose to fail and that will prevent an
infinite loop.  Thanks Niv.