[PATCH 1/4] fs: add SEEK_HOLE and SEEK_DATA flags

[Greg Freemyer]

On Aug 20, 2011 5:52 AM, "Marco Stornelli" <marco.stornelli at gmail.com>
wrote:
>
> 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)?
>

Marco,

You may want to enable the xfstests test(s) for SEEK_HOLE and SEEK_DATA for
pramfs.  That should give you some confidence your implementing the api like
other filesystems are.

Greg
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