xfs: handle zeroing in xfs_file_iomap_begin_delay

We only need to allocate blocks for zeroing for reflink inodes,
and for we currently have a special case for reflink files in
the otherwise direct I/O path that I'd like to get rid of.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

1 files changed, 38 insertions, 6 deletions

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 6320aca39f39..9b572a1fbd42 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -62,6 +62,21 @@ xfs_bmbt_to_iomap(
         iomap->dax_dev = xfs_find_daxdev_for_inode(VFS_I(ip));
 }
 
+static void
+xfs_hole_to_iomap(
+        struct xfs_inode        *ip,
+        struct iomap            *iomap,
+        xfs_fileoff_t           offset_fsb,
+        xfs_fileoff_t           end_fsb)
+{
+        iomap->addr = IOMAP_NULL_ADDR;
+        iomap->type = IOMAP_HOLE;
+        iomap->offset = XFS_FSB_TO_B(ip->i_mount, offset_fsb);
+        iomap->length = XFS_FSB_TO_B(ip->i_mount, end_fsb - offset_fsb);
+        iomap->bdev = xfs_find_bdev_for_inode(VFS_I(ip));
+        iomap->dax_dev = xfs_find_daxdev_for_inode(VFS_I(ip));
+}
+
 xfs_extlen_t
 xfs_eof_alignment(
         struct xfs_inode        *ip,
@@ -502,6 +517,7 @@ xfs_file_iomap_begin_delay(
         struct inode            *inode,
         loff_t                  offset,
         loff_t                  count,
+        unsigned                flags,
         struct iomap            *iomap)
 {
         struct xfs_inode        *ip = XFS_I(inode);
@@ -538,13 +554,23 @@ xfs_file_iomap_begin_delay(
                         goto out_unlock;
         }
 
+        end_fsb = min(XFS_B_TO_FSB(mp, offset + count), maxbytes_fsb);
+
         eof = !xfs_iext_lookup_extent(ip, ifp, offset_fsb, &icur, &got);
-        if (!eof && got.br_startoff <= offset_fsb) {
-                if (xfs_is_reflink_inode(ip)) {
+        if (eof)
+                got.br_startoff = end_fsb; /* fake hole until the end */
+
+        if (got.br_startoff <= offset_fsb) {
+                /*
+                 * For reflink files we may need a delalloc reservation when
+                 * overwriting shared extents.   This includes zeroing of
+                 * existing extents that contain data.
+                 */
+                if (xfs_is_reflink_inode(ip) &&
+                    ((flags & IOMAP_WRITE) ||
+                     got.br_state != XFS_EXT_UNWRITTEN)) {
                         bool            shared;
 
-                        end_fsb = min(XFS_B_TO_FSB(mp, offset + count),
-                                        maxbytes_fsb);
                         xfs_trim_extent(&got, offset_fsb, end_fsb - offset_fsb);
                         error = xfs_reflink_reserve_cow(ip, &got, &shared);
                         if (error)
@@ -555,6 +581,11 @@ xfs_file_iomap_begin_delay(
                 goto done;
         }
 
+        if (flags & IOMAP_ZERO) {
+                xfs_hole_to_iomap(ip, iomap, offset_fsb, got.br_startoff);
+                goto out_unlock;
+        }
+
         error = xfs_qm_dqattach_locked(ip, false);
         if (error)
                 goto out_unlock;
@@ -1009,10 +1040,11 @@ xfs_file_iomap_begin(
         if (XFS_FORCED_SHUTDOWN(mp))
                 return -EIO;
 
-        if (((flags & (IOMAP_WRITE | IOMAP_DIRECT)) == IOMAP_WRITE) &&
+        if ((flags & (IOMAP_WRITE | IOMAP_ZERO)) && !(flags & IOMAP_DIRECT) &&
                         !IS_DAX(inode) && !xfs_get_extsz_hint(ip)) {
                 /* Reserve delalloc blocks for regular writeback. */
-                return xfs_file_iomap_begin_delay(inode, offset, length, iomap);
+                return xfs_file_iomap_begin_delay(inode, offset, length, flags,
+                                iomap);
         }
 
         /*