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

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Message-Id: <804BB4B7-E19F-41EE-81A3-25D4389B54B9@dilger.ca>
Date:	Tue, 20 Sep 2011 23:25:40 -0600
From:	Andreas Dilger <adilger@...ger.ca>
To:	mtk.manpages@...il.com
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

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.

Cheers, Andreas





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