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

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Message-ID: <4E4F814B.5070202@gmail.com>
Date:	Sat, 20 Aug 2011 11:41:31 +0200
From:	Marco Stornelli <marco.stornelli@...il.com>
To:	Josef Bacik <josef@...hat.com>
CC:	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

Hi,

Il 28/06/2011 17:33, Josef Bacik ha scritto:
> This just gets us ready to support the SEEK_HOLE and SEEK_DATA flags.  Turns out
> using fiemap in things like cp cause more problems than it solves, so lets try
> and give userspace an interface that doesn't suck.  We need to match solaris
> here, and the definitions are
>
> *o* If /whence/ is SEEK_HOLE, the offset of the start of the
> next hole greater than or equal to the supplied offset
> is returned. The definition of a hole is provided near
> the end of the DESCRIPTION.
>
> *o* If /whence/ is SEEK_DATA, the file pointer is set to the
> start of the next non-hole file region greater than or
> equal to the supplied offset.
>

I'm implementing the SEEK_DATA/SEEK_HOLE management for pramfs and I've 
got some doubts about the right behavior:

1) when we use SEEK_DATA/SEEK_HOLE, the offset used in lseek means 
always the offset from the start of the file, right?

2) in case of a file with hole at the beginning and data at the end, if 
I do lseek(fd, 0, SEEK_HOLE) I should receive the end of the file 
because the idea is to search the *next* hole and we have always a 
virtual hole at the end of the file, right?

3) about the last sentence of point 2), is it always true even if we 
have a case of block allocation beyond the end of file (fallocate with 
keep size option)?

Thanks.

Regards,

Marco
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