linux-kernel - Re: [PATCH 1/4] fs: add SEEK_HOLE and SEEK

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Date:	Mon, 22 Aug 2011 08:57:51 -0700
From:	Sunil Mushran <sunil.mushran@...cle.com>
To:	Marco Stornelli <marco.stornelli@...il.com>
CC:	Josef Bacik <josef@...hat.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-btrfs@...r.kernel.org,
	xfs@....sgi.com, viro@...iv.linux.org.uk
Subject: Re: [PATCH 1/4] fs: add SEEK_HOLE and SEEK_DATA flags

On 08/22/2011 03:56 AM, Marco Stornelli wrote:
> 2011/8/22 Sunil Mushran<sunil.mushran@...cle.com>:
>> On 08/20/2011 09:32 AM, Marco Stornelli wrote:
>>> Thank. Yes the word "next" is not very clear. I re-read the proposal for
>>> the standard, actually it's seems to me that if we are in the last hole we
>>> should return the file size, if we are not in the last hole than it's ok the
>>> same offset - "....except that
>>> if offset falls beyond the last byte not within a hole, then the file
>>> offset may be set to the file size instead".
>> Any proposal that differentiates between holes is wrong. It should not
>> matter where the hole is.
>>
>> Think of it from the usage-pov.
>>
>> doff = 0;
>> while ((doff = lseek(SEEK_DATA, doff)) != -ENXIO) {
>>     hoff = lseek(SEEK_HOLE, doff);
>>     read_offset = doff;
>>     read_len = hoff -doff;
>>     process();
>>     doff = hoff;
>> }
>>
>> The goal is to make this as efficient as follows. Treating the last
>> hole differently adds more code for no benefit.
>>
> Mmmm.....It seems that Josef has to be clear in this point. However I
> looked for the seek hole test in xfs test suite, but I didn't find
> anything. Btrfs guys, how have you got tested the implementation? What
> do you think about this corner case? Al, what do you think about it?


The following test was used to test the early implementations.
http://oss.oracle.com/~smushran/seek_data/
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