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    Subject[PATCH 1/2] vfs: add FALLOC_FL_ZERO_RANGE to fallocate
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    Add a new operation mode to fallocate, called FALLOC_FL_ZERO_RANGE.
    It resembles the similarly named XFS ioctl. Filesystems should
    preallocate blocks for regions that span holes in the file, and convert
    the entire range to unwritten extents. This operation is a fast method
    of overwriting any from the range specified with zeros without removing
    any blocks or having to write zeros to disk. Any subsequent read in
    the given range will return zeros until new data is written.

    This functionality requires filesystems to support unwritten extents.
    If xfs_info(8) reports unwritten=1, then the filesystem was made to
    flag unwritten extents. It is okay to report EOPNOTSUPP and let the
    application deal with the outcome, but it is not okay to succeed or
    report EOPNOTSUPP for the same inode depending on the other arguments.

    FALLOC_FL_PUNCH_HOLE|FALLOC_FL_ZERO_RANGE is ruled out here, at the
    vfs level, rather than leaving it to the filesystems. This way, in the
    future 0x6 could be used as a third mode.

    Cc: Al Viro <viro@zeniv.linux.org.uk>
    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
    ---
    fs/open.c | 8 +++++++-
    include/linux/falloc.h | 1 +
    2 files changed, 8 insertions(+), 1 deletions(-)

    diff --git a/fs/open.c b/fs/open.c
    index d6c79a0..dd812b3 100644
    --- a/fs/open.c
    +++ b/fs/open.c
    @@ -222,8 +222,14 @@ int do_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
    if (offset < 0 || len <= 0)
    return -EINVAL;

    + /* Punch hole and write-zeroes are mutually exclusive */
    + if ((mode & FALLOC_FL_PUNCH_HOLE) &&
    + (mode & FALLOC_FL_ZERO_RANGE))
    + return -EINVAL;
    +
    /* Return error if mode is not supported */
    - if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
    + if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE |
    + FALLOC_FL_ZERO_RANGE))
    return -EOPNOTSUPP;

    /* Punch hole must have keep size set */
    diff --git a/include/linux/falloc.h b/include/linux/falloc.h
    index 73e0b62..9aa9599 100644
    --- a/include/linux/falloc.h
    +++ b/include/linux/falloc.h
    @@ -3,6 +3,7 @@

    #define FALLOC_FL_KEEP_SIZE 0x01 /* default is extend size */
    #define FALLOC_FL_PUNCH_HOLE 0x02 /* de-allocates range */
    +#define FALLOC_FL_ZERO_RANGE 0x04 /* write zeroes */

    #ifdef __KERNEL__

    --
    1.7.1



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