linux-kernel - Re: [PATCH] fallocate.2: add FALLOC_FL_PUNCH

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Date:	Wed, 21 Sep 2011 07:49:33 +0200
From:	Michael Kerrisk <mtk.manpages@...il.com>
To:	Andreas Dilger <adilger@...ger.ca>
Cc:	Josef Bacik <josef@...hat.com>, Eric Gouriou <egouriou@...gle.com>,
	inux-man@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Lucian Adrian Grijincu <lucian.grijincu@...il.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Dave Chinner <dchinner@...hat.com>
Subject: Re: [PATCH] fallocate.2: add FALLOC_FL_PUNCH_HOLE flag definition

Hello Andreas,

On Wed, Sep 21, 2011 at 7:25 AM, Andreas Dilger <adilger@...ger.ca> wrote:
> On 2011-09-20, at 10:11 PM, Michael Kerrisk wrote:
>> Thanks for this patch. As noted in another mail, Lucian also sent a
>> patch for FALLOC_FL_PUNCH_HOLE, and I applied his patch first, and
>> then added some pieces from yours, as well as some of my own edits.
>>
>> However, the addition of a second class of operation to the man page
>> made it clear that some significant restructuring of the page is
>> required. So I substantially reworked the page, including the
>> preexisting material on the default "file allocation" operation (Dave
>> C please note).
>>
>>  .TP
>> .B EINVAL
>> .I offset
>> was less than 0, or
>> .I len
>> was less than or equal to 0.
>
> I wasn't sure if this is a bug in the manpage or actually how it is done
> in the kernel, but it seems this is a kernel implementation issue...
>
> Does it make sense to return an error if len == 0?  That just adds extra
> complexity on the part of the application, and doesn't reduce complexity
> in the kernel (whether the kernel checks for len == 0 and returns 0 or
> -EINVAL is not any different).  read() and write() and malloc() all allow
> a length of zero to succeed, since applications may compute this length
> and sometimes it is zero.

Good point. I agree: for comfort of userspace application writers and
for consistency with related interfaces, len == 0 shouldn't be an
error.

Cheers,

Michael

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Author of "The Linux Programming Interface"; http://man7.org/tlpi/
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