[lkml]   [2010]   [Nov]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: [PATCH 1/6] fs: add hole punching to fallocate
    On Mon, Nov 08, 2010 at 03:32:02PM -0500, Josef Bacik wrote:
    > Hole punching has already been implemented by XFS and OCFS2, and has the
    > potential to be implemented on both BTRFS and EXT4 so we need a generic way to
    > get to this feature. The simplest way in my mind is to add FALLOC_FL_PUNCH_HOLE
    > to fallocate() since it already looks like the normal fallocate() operation.
    > I've tested this patch with XFS and BTRFS to make sure XFS did what it's
    > supposed to do and that BTRFS failed like it was supposed to. Thank you,
    > Signed-off-by: Josef Bacik <>
    > ---
    > fs/open.c | 2 +-
    > include/linux/falloc.h | 1 +
    > 2 files changed, 2 insertions(+), 1 deletions(-)
    > diff --git a/fs/open.c b/fs/open.c
    > index 4197b9e..ab8dedf 100644
    > --- a/fs/open.c
    > +++ b/fs/open.c
    > @@ -223,7 +223,7 @@ int do_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
    > return -EINVAL;
    > /* Return error if mode is not supported */
    > - if (mode && !(mode & FALLOC_FL_KEEP_SIZE))
    > + if (mode && (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE)))
    > return -EOPNOTSUPP;
    > if (!(file->f_mode & FMODE_WRITE))
    > diff --git a/include/linux/falloc.h b/include/linux/falloc.h
    > index 3c15510..851cba2 100644
    > --- a/include/linux/falloc.h
    > +++ b/include/linux/falloc.h
    > @@ -2,6 +2,7 @@
    > #define _FALLOC_H_
    > #define FALLOC_FL_KEEP_SIZE 0x01 /* default is extend size */
    > +#define FALLOC_FL_PUNCH_HOLE 0X02 /* de-allocates range */

    Hole punching was not included originally in fallocate() for a
    variety of reasons. IIRC, they were along the lines of:

    1 de-allocating of blocks in an allocation syscall is wrong.
    People wanted a new syscall for this functionality.
    2 no glibc interface needs it
    3 at the time, only XFS supported punching holes, so there
    is not need to support it in a generic interface
    4 the use cases presented were not considered compelling
    enough to justify the additional complexity (!)

    In the end, I gave up arguing for it to be included because just
    getting the FALLOC_FL_KEEP_SIZE functionality was a hard enough

    Anyway, #3 isn't the case any more, #4 was just an excuse not to
    support anything ext4 couldn't do and lots of apps are calling
    fallocate directly (because glibc can't use FALLOC_FL_KEEP_SIZE) so
    #2 isn't an issue, either. I guess that leaves #1 to be debated;
    I don't think there is any problem with doing what you propose.

    What I will suggest is that this requires a generic xfstest to be
    written and support added to xfs_io to enable that test (and others)
    to issue hole punches. Something along the lines of test 242 which I
    wrote for testing all the edge case of XFS_IOC_ZERO_RANGE (*) would be



    (*) fallocate() version:;a=commitdiff;h=45f3e1831e3abc8bd12ec1e6c548f73a8dd9e36d
    Dave Chinner

     \ /
      Last update: 2010-11-09 02:15    [W:0.023 / U:0.284 seconds]
    ©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site