Re: [PATCH v5 10/10] manpage: update FALLOC_FL_COLLAPSE_RANGE flag in fallocate

["Michael Kerrisk (man-pages)" <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On 04/18/2014 12:57 AM, Dave Chinner wrote:
> On Thu, Apr 17, 2014 at 03:40:05PM +0200, Michael Kerrisk (man-pages) wrote:
>> On 04/16/2014 08:05 AM, Christoph Hellwig wrote:
>>> Michael, can you apply this now that we merged FALLOC_FL_COLLAPSE_RANGE
>>> into the kernel tree?
>>
>> I've applied Namjae Jeon's patch (thanks Namjae!), and done a lot of
>> tweaking to generate the patch below.
>>
>> Along the way I noticed that there is an inconsistency between XFS
>> and JFS that should be fixed (and so have added Dave and Ted to CC,
>> as well as linux-fsdevel@). 
>>
>> If 'fd' does not refer to a regular file, then XFS fails with the 
>> error EINVAL (fs/xfs/xfs_file.c::xfs_file_fallocate()), but ext4 
>> fails with the error EOPNOTSUP
>> (fs/ext4/extents::ext4_collapse_range()). I suspect that EINVAL
>> is the right error for this case.
> 
> I think EINVAL is correct here - we support the syscall, just the
> type of file we are being asked to operate on is invalid.

Hmmm -- you and Lukasz seem to differ on this point.

> FWIW, the reason this check is in the filesystems is that there is
> no theoretical reason why we can't do things like preallocation for
> directories (e.g. to reduce fragmentation as they grow). It's just
> not implemented by any filesystem yet.
> 
> [ Hmmmm -  I just had a great idea - removing entire directory
> contents via punching blocks. No more "remove one dirent at a time"
> for rm -rf, just punch the directory from start to end and there
> goes millions of directory entries in a single syscall and a handful
> of transactions.  FALLOC_FL_DIR_PUNCH, anyone? ]

Interesting idea. CC me and linux-api on the patch, if you do one.

>> I'd appreciate review on my revised patch, below.
> 
> Looks fine to me.

Thanks,

Michael


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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