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Re: [PATCH 1/2] fiemap: add freespace mapping to FS_IOC_FIEMAP

To: Mark Tinguely <tinguely@xxxxxxx>
Subject: Re: [PATCH 1/2] fiemap: add freespace mapping to FS_IOC_FIEMAP
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Fri, 9 Nov 2012 07:56:48 +1100
Cc: linux-fsdevel@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
In-reply-to: <509BE2E9.1070702@xxxxxxx>
References: <1350537079-16246-1-git-send-email-david@xxxxxxxxxxxxx> <1350537079-16246-2-git-send-email-david@xxxxxxxxxxxxx> <509BE2E9.1070702@xxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Thu, Nov 08, 2012 at 10:50:49AM -0600, Mark Tinguely wrote:
> On 10/18/12 00:11, Dave Chinner wrote:
> >From: Dave Chinner<dchinner@xxxxxxxxxx>
> >
> >fiemap is used to map extents of used space on files. it's just an
> >array of extents, though, so there's no reason it can only index
> >*used*  space.
> >
> >Ther eis need for getting freespace layout information into
> >userspace. For example, defragmentation programs would find it
> >useful to be able to map the free space in the filesystem to
> >work out where it is best to move data to defragment it.
> >Alternatively, knowing where free space is enables us to identify
> >extents that need to be moved to defragment free space.
> >
> >Hence, extend fiemap with the FIEMAP_FLAG_FREESPACE to indicate that
> >the caller wants to map free space in the range fm_start bytes from
> >the start of the filesystem for fm_length bytes.
> >
> >Because XFS can report extents in size order without needing to
> >sort, and this information is useful to xfs_fsr, also add
> >FIEMAP_FLAG_FREESPACE_SIZE to tell the filesystem to return a
> >freespace map ordered by extent size rather than offset. If there
> >are multiple extents of the same size, then they are ordered by
> >offset.
> >
> >Signed-off-by: Dave Chinner<dchinner@xxxxxxxxxx>
> >---
> ...
> >  --------------
> >diff --git a/include/linux/fiemap.h b/include/linux/fiemap.h
> >index d830747..f4fbb9f 100644
> >--- a/include/linux/fiemap.h
> >+++ b/include/linux/fiemap.h
>   include/uabi/linux/fiemap.h
>           ^^^^
> other than that, it looks good.

include/uapi/ actaully, but that change was made after I posted the
patches so there's no surprise that It didn't apply.

As it is, this needs to be redone into an FS_IOC_FIEMAPFS ioctl in
response to other reviews. I've already done that work (a week ago),
I just haven't fully tested it yet so I haven't reported it...


Dave Chinner

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