xfs: Introduce XFS_IOC_ZERO_RANGE

XFS_IOC_ZERO_RANGE is the equivalent of an atomic XFS_IOC_UNRESVSP/
XFS_IOC_RESVSP call pair. It enabled ranges of written data to be
turned into zeroes without requiring IO or having to free and
reallocate the extents in the range given as would occur if we had
to punch and then preallocate them separately.  This enables
applications to zero parts of files very quickly without changing
the layout of the files in any way.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

1 files changed, 8 insertions, 2 deletions

diff --git a/fs/xfs/xfs_vnodeops.c b/fs/xfs/xfs_vnodeops.c
index 4c7c7bfb2b2f..dc6e4fb8bbc9 100644
--- a/fs/xfs/xfs_vnodeops.c
+++ b/fs/xfs/xfs_vnodeops.c
@@ -2272,7 +2272,7 @@ xfs_alloc_file_space(
         count = len;
         imapp = &imaps[0];
         nimaps = 1;
-        bmapi_flag = XFS_BMAPI_WRITE | (alloc_type ? XFS_BMAPI_PREALLOC : 0);
+        bmapi_flag = XFS_BMAPI_WRITE | alloc_type;
         startoffset_fsb = XFS_B_TO_FSBT(mp, offset);
         allocatesize_fsb = XFS_B_TO_FSB(mp, count);
 
@@ -2711,6 +2711,7 @@ xfs_change_file_space(
         xfs_off_t       llen;
         xfs_trans_t     *tp;
         struct iattr    iattr;
+        int             prealloc_type;
 
         if (!S_ISREG(ip->i_d.di_mode))
                 return XFS_ERROR(EINVAL);
@@ -2753,12 +2754,17 @@ xfs_change_file_space(
          * size to be changed.
          */
         setprealloc = clrprealloc = 0;
+        prealloc_type = XFS_BMAPI_PREALLOC;
 
         switch (cmd) {
+        case XFS_IOC_ZERO_RANGE:
+                prealloc_type |= XFS_BMAPI_CONVERT;
+                xfs_tosspages(ip, startoffset, startoffset + bf->l_len, 0);
+                /* FALLTHRU */
         case XFS_IOC_RESVSP:
         case XFS_IOC_RESVSP64:
                 error = xfs_alloc_file_space(ip, startoffset, bf->l_len,
-                                                                1, attr_flags);
+                                                prealloc_type, attr_flags);
                 if (error)
                         return error;
                 setprealloc = 1;