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From: NeilBrown <neilb@suse.de>
To: Christoph Hellwig <hch@infradead.org>
Cc: David Howells <dhowells@redhat.com>, Chris Mason <clm@fb.com>,
	Al Viro <viro@ZenIV.linux.org.uk>, Josef Bacik <jbacik@fb.com>,
	David Sterba <dsterba@suse.cz>,
	Dave Chinner <david@fromorbit.com>,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-btrfs@vger.kernel.org
Subject: Re: [PATCH 3/3] btrfs: set FS_SUPPORTS_SEEK_HOLE flag.
Date: Mon, 27 Apr 2015 15:41:33 +1000	[thread overview]
Message-ID: <20150427154133.65f58366@notabene.brown> (raw)
In-Reply-To: <20150420094855.GA21116@infradead.org>

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On Mon, 20 Apr 2015 02:48:55 -0700 Christoph Hellwig <hch@infradead.org>
wrote:

> On Mon, Apr 20, 2015 at 10:46:49AM +0100, David Howells wrote:
> > NeilBrown <neilb@suse.de> wrote:
> > 
> > > Missing patch 2 of the 3-patch series?
> > 
> > Yes. :-)
> > 
> > Do ext4 and xfs support this, do you know?
> 
> Yes.  As do f2fs, ocfs2, gfs2, ceph and NFSv4.2

Are you sure about NFSv4.2?

I see that it *can* report holes, but is there any guarantee that if you
create a new file and write only the 5th block, then READ_PLUS will reliably
report that the first 4 block are holes??

Because if it doesn't guarantee that, then NFSv4.2 doesn't fit the with the
others where SEEK_HOLE reliable reports holes.
On the other hand if NFSv4.2 *does* guarantee that then the current READ_PLUS
server patches are broken because they just use vfs_llseek and assume that
trust what it says.

It would be really nice if SEEK_{DATA,HOLE} either reported holes reliably or
returned ENXIO, but I guess there was a goo reason not to do that.

Thanks,
NeilBrown

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  parent reply	other threads:[~2015-04-27  5:41 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-04-20  5:27 [PATCH 0/3] Allow fscache to work on BTRFS NeilBrown
2015-04-20  5:27 ` [PATCH 1/3] cachefiles: perform test on s_blocksize when opening cache file NeilBrown
2015-04-20  5:27 ` [PATCH 2/3] fscache/cachefiles: optionally use SEEK_DATA instead of ->bmap NeilBrown
2015-04-20  6:08   ` Christoph Hellwig
2015-04-20  6:27     ` NeilBrown
2015-04-20  9:45       ` Christoph Hellwig
2015-04-21 23:06         ` NeilBrown
2015-04-20  5:27 ` [PATCH 3/3] btrfs: set FS_SUPPORTS_SEEK_HOLE flag NeilBrown
2015-04-20 19:48   ` Chris Mason
2015-04-20  8:47 ` David Howells
2015-04-20  9:33   ` NeilBrown
2015-04-20  9:46   ` David Howells
2015-04-20  9:48     ` Christoph Hellwig
2015-04-20 12:58       ` Al Viro
2015-04-21  8:43         ` Christoph Hellwig
2015-04-21 10:23           ` Hugh Dickins
2015-04-27  5:41       ` NeilBrown [this message]
2015-04-27 13:43         ` Christoph Hellwig
2015-04-20 11:21 ` [PATCH 2/3] fscache/cachefiles: optionally use SEEK_DATA instead of ->bmap David Howells
2015-04-20 15:59 ` [RFC][PATCH] cachefiles: Make better use of SEEK_DATA/SEEK_HOLE David Howells

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