[lkml]   [2007]   [May]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: [PATCH 1/5] fallocate() implementation in i86, x86_64 and powerpc
    On Wed, May 09, 2007 at 09:31:02PM +0530, Amit K. Arora wrote:
    > I have the updated patches ready which take care of Andrew's comments.
    > Will run some tests and post them soon.
    > But, before submitting these patches, I think it will be better to finalize
    > on certain things which might be worth some discussion here:
    > 1) Should the file size change when preallocation is done beyond EOF ?
    > - Andreas and Chris Wedgwood are in favor of not changing the
    > file size in this case. I also tend to agree with them. Does anyone
    > has an argument in favor of changing the filesize ?
    > If not, I will remove the code which changes the filesize, before I
    > resubmit the concerned ext4 patch.

    I think there needs to be both. If we don't have a mechanism to
    atomically change the file size with the preallocation, then
    applications that use stat() to work out if they need to preallocate
    more space will end up racing.

    > 2) For FA_UNALLOCATE mode, should the file system allow unallocation
    > of normal (non-preallocated) blocks (blocks allocated via
    > regular write/truncate operations) also (i.e. work as punch()) ?

    Yes. That is the current XFS implementation for XFS_IOC_UNRESVSP, and
    what i did for FA_UNALLOCATE as well.

    > - Though FA_UNALLOCATE mode is yet to be implemented on ext4, still
    > we need to finalize on the convention here as a general guideline
    > to all the filesystems that implement fallocate.
    > 3) If above is true, the file size will need to be changed
    > for "unallocation" when block holding the EOF gets unallocated.

    No - we punch a hole. If you want the filesize to change, then
    you use ftruncate() to remove the blocks at EOF and change the
    file size atomically.

    > 4) Should we update mtime & ctime on a successfull allocation/
    > unallocation ?
    > - David Chinner raised this question in following post:
    > I think it makes sense to update the [mc]time for a successfull
    > preallocation/unallocation. Does anyone feel otherwise ?
    > It will be interesting to know how XFS behaves currently. Does XFS
    > update [mc]time for preallocation ?

    No, XFS does *not* update a/m/ctime on prealloc/punch unless the file size
    changes. If the filesize changes, it behaves exactly the same way that
    ftruncate() behaves.


    Dave Chinner
    Principal Engineer
    SGI Australian Software Group
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to
    More majordomo info at
    Please read the FAQ at

     \ /
      Last update: 2007-05-10 03:03    [W:0.023 / U:66.928 seconds]
    ©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site