From: Dave Chinner <david@fromorbit.com>
To: David Howells <dhowells@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>,
Carlos Maiolino <cmaiolino@redhat.com>,
linux-fsdevel@vger.kernel.org, adilger@dilger.ca,
jaegeuk@kernel.org, darrick.wong@oracle.com, miklos@szeredi.hu,
rpeterso@redhat.com, linux-xfs@vger.kernel.org
Subject: Re: [PATCH 2/9] cachefiles: drop direct usage of ->bmap method.
Date: Fri, 6 Sep 2019 08:44:03 +1000 [thread overview]
Message-ID: <20190905224403.GK1119@dread.disaster.area> (raw)
In-Reply-To: <28402.1567212357@warthog.procyon.org.uk>
On Sat, Aug 31, 2019 at 01:45:57AM +0100, David Howells wrote:
> Christoph Hellwig <hch@lst.de> wrote:
>
> > We'll you'd need to implement a IOCB_NOHOLE, but that wouldn't be all
> > that hard. Having a READ_PLUS like interface that actually tells you
> > how large the hole is might be hard.
>
> Actually, that raises another couple of questions:
>
> (1) Is a filesystem allowed to join up two disjoint blocks of data with a
> block of zeros to make a single extent? If this happens, I'll see the
> inserted block of zeros to be valid data.
Yes.
> (2) Is a filesystem allowed to punch out a block of valid zero data to make a
> hole? This would cause me to refetch the data.
Yes.
Essentially, assumptions that filesystems will not change the file
layout even if the data does not change are invalid. copy-on-write,
deduplication, speculative preallocation, etc mean the file layout
can change even if the file data itself is not directly modified.
If you want to cache physical file layout information and be
notified when they may change, then that's what layout leases are
for....
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
next prev parent reply other threads:[~2019-09-05 22:44 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-08 8:27 [PATCH 0/9 V5] New ->fiemap infrastructure and ->bmap removal Carlos Maiolino
2019-08-08 8:27 ` [PATCH 1/9] fs: Enable bmap() function to properly return errors Carlos Maiolino
2019-08-08 21:24 ` kbuild test robot
2019-08-14 11:14 ` Christoph Hellwig
2019-08-20 11:36 ` Carlos Maiolino
2019-08-08 8:27 ` [PATCH 2/9] cachefiles: drop direct usage of ->bmap method Carlos Maiolino
2019-08-14 11:15 ` Christoph Hellwig
2019-08-20 11:57 ` Carlos Maiolino
2019-08-20 12:50 ` David Howells
2019-08-29 7:13 ` Christoph Hellwig
2019-08-30 16:17 ` David Howells
2019-08-30 16:59 ` Christoph Hellwig
2019-08-31 0:45 ` David Howells
2019-09-05 22:44 ` Dave Chinner [this message]
2019-08-20 13:31 ` David Howells
2019-08-08 8:27 ` [PATCH 3/9] ecryptfs: drop direct calls to ->bmap Carlos Maiolino
2019-08-08 22:50 ` kbuild test robot
2019-08-08 8:27 ` [PATCH 4/9] fibmap: Use bmap instead of ->bmap method in ioctl_fibmap Carlos Maiolino
2019-08-08 20:38 ` kbuild test robot
2019-08-14 11:01 ` Carlos Maiolino
2019-08-14 11:08 ` Christoph Hellwig
2019-08-08 8:27 ` [PATCH 5/9] fs: Move start and length fiemap fields into fiemap_extent_info Carlos Maiolino
2019-08-08 20:21 ` kbuild test robot
2019-08-08 8:27 ` [PATCH 6/9] iomap: Remove length and start fields from iomap_fiemap Carlos Maiolino
2019-08-08 8:27 ` [PATCH 7/9] fiemap: Use a callback to fill fiemap extents Carlos Maiolino
2019-08-09 0:04 ` kbuild test robot
2019-08-14 11:16 ` Christoph Hellwig
2019-08-08 8:27 ` [PATCH 8/9] Use FIEMAP for FIBMAP calls Carlos Maiolino
2019-08-09 1:56 ` kbuild test robot
2019-08-14 11:18 ` Christoph Hellwig
2019-08-20 13:01 ` Carlos Maiolino
2019-08-29 7:15 ` Christoph Hellwig
2019-09-10 12:28 ` Carlos Maiolino
2019-09-16 15:58 ` Darrick J. Wong
2019-08-08 8:27 ` [PATCH 9/9] xfs: Get rid of ->bmap Carlos Maiolino
-- strict thread matches above, loose matches on Subject: below --
2019-09-11 13:43 [PATCH 0/9 V6] New ->fiemap infrastructure and ->bmap removal Carlos Maiolino
2019-09-11 13:43 ` [PATCH 2/9] cachefiles: drop direct usage of ->bmap method Carlos Maiolino
2019-07-31 14:12 [PATCH 0/9 V4] New ->fiemap infrastructure and ->bmap removal Carlos Maiolino
2019-07-31 14:12 ` [PATCH 2/9] cachefiles: drop direct usage of ->bmap method Carlos Maiolino
2019-02-18 13:03 [PATCH 0/9 V3] New ->fiemap infrastructure and ->bmap removal Carlos Maiolino
2019-02-18 13:03 ` [PATCH 2/9] cachefiles: drop direct usage of ->bmap method Carlos Maiolino
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