linux-kernel - Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it

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Message-ID: <20170403184034.GI37923@jra3>
Date:   Mon, 3 Apr 2017 11:40:34 -0700
From:   Jeremy Allison <jra@...ba.org>
To:     Jeff Layton <jlayton@...hat.com>
Cc:     Matthew Wilcox <willy@...radead.org>, NeilBrown <neilb@...e.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-ext4@...r.kernel.org, akpm@...ux-foundation.org,
        tytso@....edu, jack@...e.cz
Subject: Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking
 infrastructure and convert ext4 to use it

On Mon, Apr 03, 2017 at 11:36:48AM -0700, Jeremy Allison wrote:
> On Mon, Apr 03, 2017 at 02:18:44PM -0400, Jeff Layton wrote:
> > On Mon, 2017-04-03 at 11:09 -0700, Jeremy Allison wrote:
> > > 
> > > CIFS has a way to reserve space. Look into "allocation size" on create.
> > 
> > That won't help here as it's done on open().
> > 
> > The problem here is that we might create a file (and not preallocate
> > anything), then write a bunch of stuff to the cache under an oplock.
> > Then when we go to write back, we get the CIFS equivalent of -ENOSPC.
> > 
> > What local filesystems do (AIUI) is preallocate so that you can catch
> > an ENOSPC condition earlier, when you're dirtying new pages in the
> > cache. That's pretty much impossible to do on a network filesystem
> > though.
> 
> There's also SMB_SET_FILE_ALLOCATION_INFO which can be
> done over SMB1/2/3 on an open file handle.

There's *always* a way to do something in SMB1/2/3. :-).