From: Dan Merillat <dan.merillat@gmail.com>
To: Dave Chinner <david@fromorbit.com>
Cc: Sunil Mushran <sunil.mushran@oracle.com>,
Andreas Dilger <adilger@dilger.ca>,
Christoph Hellwig <hch@infradead.org>,
Josef Bacik <josef@redhat.com>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-btrfs@vger.kernel.org, xfs@oss.sgi.com,
viro@zeniv.linux.org.uk, dchinner@redhat.com
Subject: Re: [PATCH] xfstests 255: add a seek_data/seek_hole tester
Date: Wed, 31 Aug 2011 00:48:15 -0400 [thread overview]
Message-ID: <CAPL5yKfC2-4zh26+ApAzLTOqg43rhn18TTo8vwQuDDHV5iaPhw@mail.gmail.com> (raw)
In-Reply-To: <20110831032932.GI32358@dastard>
On Tue, Aug 30, 2011 at 11:29 PM, Dave Chinner <david@fromorbit.com> wrote:
> On Tue, Aug 30, 2011 at 06:17:02PM -0700, Sunil Mushran wrote:
>> Instead
>> we should let the fs weigh the cost of providing accurate information
>> with the possible gain in performance.
>>
>> Data:
>> A range in a file that could contain something other than nulls.
>> If in doubt, it is data.
>>
>> Hole:
>> A range in a file that only contains nulls.
>
> And that's -exactly- the ambiguous, vague definition that has raised
> all these questions in the first place. I was in doubt about whether
> unwritten extents can be considered a hole, and by your definition
> that means it should be data. But Andreas seems to be in no doubt it
> should be considered a hole.
That's fine, though. Different filesystems have different abilities
to recognize a data hole - FAT can't do it at all. Perhaps the
requirements would be better stated in reverse: If the filesystem
knows that a read() will return nulls (for whatever reason based on
it's internal knowledge), it can report a hole. If it can't guarantee
that, it's data. It's an absolute requirement that SEEK_DATA never
miss data. SEEK_HOLE working is a nicety that userspace would
appreciate - remember that the consumer here is cp(1), using it to
skip empty portions of files and create sparse destination files.
WARNING: multiple messages have this Message-ID (diff)
From: Dan Merillat <dan.merillat@gmail.com>
To: Dave Chinner <david@fromorbit.com>
Cc: Sunil Mushran <sunil.mushran@oracle.com>,
Andreas Dilger <adilger@dilger.ca>,
linux-kernel@vger.kernel.org, xfs@oss.sgi.com,
Christoph Hellwig <hch@infradead.org>,
linux-btrfs@vger.kernel.org, dchinner@redhat.com,
linux-fsdevel@vger.kernel.org, Josef Bacik <josef@redhat.com>,
viro@zeniv.linux.org.uk
Subject: Re: [PATCH] xfstests 255: add a seek_data/seek_hole tester
Date: Wed, 31 Aug 2011 00:48:15 -0400 [thread overview]
Message-ID: <CAPL5yKfC2-4zh26+ApAzLTOqg43rhn18TTo8vwQuDDHV5iaPhw@mail.gmail.com> (raw)
In-Reply-To: <20110831032932.GI32358@dastard>
On Tue, Aug 30, 2011 at 11:29 PM, Dave Chinner <david@fromorbit.com> wrote:
> On Tue, Aug 30, 2011 at 06:17:02PM -0700, Sunil Mushran wrote:
>> Instead
>> we should let the fs weigh the cost of providing accurate information
>> with the possible gain in performance.
>>
>> Data:
>> A range in a file that could contain something other than nulls.
>> If in doubt, it is data.
>>
>> Hole:
>> A range in a file that only contains nulls.
>
> And that's -exactly- the ambiguous, vague definition that has raised
> all these questions in the first place. I was in doubt about whether
> unwritten extents can be considered a hole, and by your definition
> that means it should be data. But Andreas seems to be in no doubt it
> should be considered a hole.
That's fine, though. Different filesystems have different abilities
to recognize a data hole - FAT can't do it at all. Perhaps the
requirements would be better stated in reverse: If the filesystem
knows that a read() will return nulls (for whatever reason based on
it's internal knowledge), it can report a hole. If it can't guarantee
that, it's data. It's an absolute requirement that SEEK_DATA never
miss data. SEEK_HOLE working is a nicety that userspace would
appreciate - remember that the consumer here is cp(1), using it to
skip empty portions of files and create sparse destination files.
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next prev parent reply other threads:[~2011-08-31 4:48 UTC|newest]
Thread overview: 106+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-06-28 15:33 [PATCH 1/4] fs: add SEEK_HOLE and SEEK_DATA flags Josef Bacik
2011-06-28 15:33 ` Josef Bacik
2011-06-28 15:33 ` [PATCH 2/4] Btrfs: implement our own ->llseek Josef Bacik
2011-06-28 15:33 ` Josef Bacik
2011-06-28 15:33 ` [PATCH 3/4] Ext4: handle SEEK_HOLE/SEEK_DATA generically Josef Bacik
2011-06-28 15:33 ` Josef Bacik
2011-06-28 16:29 ` Andreas Dilger
2011-06-28 17:34 ` Josef Bacik
2011-06-28 15:33 ` [PATCH 4/4] fs: handle SEEK_HOLE/SEEK_DATA properly in all fs's that define their own llseek Josef Bacik
2011-06-28 15:33 ` Josef Bacik
2011-06-28 15:33 ` [PATCH] xfstests 255: add a seek_data/seek_hole tester Josef Bacik
2011-06-28 15:33 ` Josef Bacik
2011-06-29 6:53 ` Dave Chinner
2011-06-29 6:53 ` Dave Chinner
2011-06-29 6:53 ` Dave Chinner
2011-06-29 6:53 ` Dave Chinner
2011-06-29 7:40 ` Christoph Hellwig
2011-06-29 7:40 ` Christoph Hellwig
2011-06-29 10:42 ` Pádraig Brady
2011-06-29 10:42 ` Pádraig Brady
2011-06-29 10:42 ` Pádraig Brady
2011-06-29 10:42 ` Pádraig Brady
2011-06-29 17:29 ` Sunil Mushran
2011-06-29 17:29 ` Sunil Mushran
2011-06-29 17:29 ` Sunil Mushran
2011-06-29 17:29 ` Sunil Mushran
2011-06-29 17:36 ` Christoph Hellwig
2011-06-29 17:36 ` Christoph Hellwig
2011-06-29 17:40 ` Sunil Mushran
2011-06-29 17:40 ` Sunil Mushran
2011-06-29 21:29 ` Pádraig Brady
2011-06-29 21:29 ` Pádraig Brady
2011-06-29 21:29 ` Pádraig Brady
2011-07-01 9:37 ` Christoph Hellwig
2011-07-01 9:37 ` Christoph Hellwig
2011-06-29 17:10 ` Sunil Mushran
2011-06-29 17:10 ` Sunil Mushran
2011-06-29 17:52 ` Josef Bacik
2011-06-29 17:52 ` Josef Bacik
2011-06-29 13:19 ` Josef Bacik
2011-06-29 13:19 ` Josef Bacik
2011-06-29 13:19 ` Josef Bacik
2011-08-25 6:06 ` Christoph Hellwig
2011-08-25 6:06 ` Christoph Hellwig
2011-08-25 6:40 ` Dave Chinner
2011-08-25 6:40 ` Dave Chinner
2011-08-25 6:51 ` Andreas Dilger
2011-08-25 6:51 ` Andreas Dilger
2011-08-26 1:35 ` Dave Chinner
2011-08-26 1:35 ` Dave Chinner
2011-08-26 6:24 ` Marco Stornelli
2011-08-26 6:24 ` Marco Stornelli
2011-08-26 6:24 ` Marco Stornelli
2011-08-26 14:41 ` Zach Brown
2011-08-26 14:41 ` Zach Brown
2011-08-26 14:41 ` Zach Brown
2011-08-26 14:41 ` Zach Brown
2011-08-27 8:30 ` Marco Stornelli
2011-08-27 8:30 ` Marco Stornelli
2011-08-28 10:17 ` Marco Stornelli
2011-08-28 10:17 ` Marco Stornelli
2011-08-30 17:42 ` Sunil Mushran
2011-08-30 17:42 ` Sunil Mushran
2011-08-31 1:17 ` Sunil Mushran
2011-08-31 1:17 ` Sunil Mushran
2011-08-31 3:29 ` Dave Chinner
2011-08-31 3:29 ` Dave Chinner
2011-08-31 3:53 ` david
2011-08-31 3:53 ` david
2011-08-31 4:43 ` Sunil Mushran
2011-08-31 4:43 ` Sunil Mushran
2011-08-31 9:05 ` Pádraig Brady
2011-08-31 9:05 ` Pádraig Brady
2011-08-31 9:05 ` Pádraig Brady
2011-08-31 4:48 ` Dan Merillat [this message]
2011-08-31 4:48 ` Dan Merillat
2011-07-29 9:58 ` [PATCH 1/4] fs: add SEEK_HOLE and SEEK_DATA flags Marco Stornelli
2011-07-29 9:58 ` Marco Stornelli
2011-08-20 9:41 ` Marco Stornelli
2011-08-20 9:41 ` Marco Stornelli
2011-08-20 10:03 ` Marco Stornelli
2011-08-20 10:03 ` Marco Stornelli
2011-08-20 15:36 ` Sunil Mushran
2011-08-20 15:36 ` Sunil Mushran
2011-08-20 16:32 ` Marco Stornelli
2011-08-20 16:32 ` Marco Stornelli
2011-08-22 6:08 ` Sunil Mushran
2011-08-22 6:08 ` Sunil Mushran
2011-08-22 10:56 ` Marco Stornelli
2011-08-22 10:56 ` Marco Stornelli
2011-08-22 10:56 ` Marco Stornelli
2011-08-22 10:56 ` Marco Stornelli
2011-08-22 15:57 ` Sunil Mushran
2011-08-22 15:57 ` Sunil Mushran
2011-08-22 17:56 ` Marco Stornelli
2011-08-22 17:56 ` Marco Stornelli
2011-08-22 21:22 ` Sunil Mushran
2011-08-22 21:22 ` Sunil Mushran
2011-08-23 17:44 ` Marco Stornelli
2011-08-23 17:44 ` Marco Stornelli
2011-08-31 0:35 ` Dave Chinner
2011-08-31 0:35 ` Dave Chinner
[not found] ` <CAGpXXZ+xjhadprkc_LiP3qUypLLkCxdeEmo8+K+6mOnBuNhmLg@mail.gmail.com>
2011-08-20 17:18 ` Greg Freemyer
-- strict thread matches above, loose matches on Subject: below --
2011-06-27 18:02 Josef Bacik
2011-06-27 18:02 ` [PATCH] xfstests 255: add a seek_data/seek_hole tester Josef Bacik
2011-06-27 18:32 ` Andreas Dilger
2011-06-27 18:47 ` Josef Bacik
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