xfs: add xfs_trim_extent

This helpers allows to trim an extent to a subset of it's original range
while making sure the block numbers in it remain valid,

In the future xfs_trim_extent and xfs_bmapi_trim_map should probably be
merged in some form.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
[hch: split from a previous patch from Darrick, moved around and added
 support for "raw" delayed extents"]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
index 80bdb11..381e765 100644 (file)
--- a/fs/xfs/libxfs/xfs_bmap.c
+++ b/fs/xfs/libxfs/xfs_bmap.c
@@ -3996,6 +3996,39 @@ xfs_bmap_alloc(
        return xfs_bmap_btalloc(ap);
 }
 
+/* Trim extent to fit a logical block range. */
+void
+xfs_trim_extent(
+       struct xfs_bmbt_irec    *irec,
+       xfs_fileoff_t           bno,
+       xfs_filblks_t           len)
+{
+       xfs_fileoff_t           distance;
+       xfs_fileoff_t           end = bno + len;
+
+       if (irec->br_startoff + irec->br_blockcount <= bno ||
+           irec->br_startoff >= end) {
+               irec->br_blockcount = 0;
+               return;
+       }
+
+       if (irec->br_startoff < bno) {
+               distance = bno - irec->br_startoff;
+               if (isnullstartblock(irec->br_startblock))
+                       irec->br_startblock = DELAYSTARTBLOCK;
+               if (irec->br_startblock != DELAYSTARTBLOCK &&
+                   irec->br_startblock != HOLESTARTBLOCK)
+                       irec->br_startblock += distance;
+               irec->br_startoff += distance;
+               irec->br_blockcount -= distance;
+       }
+
+       if (end < irec->br_startoff + irec->br_blockcount) {
+               distance = irec->br_startoff + irec->br_blockcount - end;
+               irec->br_blockcount -= distance;
+       }
+}
+
 /*
  * Trim the returned map to the required bounds
  */

diff --git a/fs/xfs/libxfs/xfs_bmap.h b/fs/xfs/libxfs/xfs_bmap.h
index f97db71..eb86af0 100644 (file)
--- a/fs/xfs/libxfs/xfs_bmap.h
+++ b/fs/xfs/libxfs/xfs_bmap.h
@@ -190,6 +190,8 @@ void        xfs_bmap_trace_exlist(struct xfs_inode *ip, xfs_extnum_t cnt,
 #define        XFS_BMAP_TRACE_EXLIST(ip,c,w)
 #endif
 
+void   xfs_trim_extent(struct xfs_bmbt_irec *irec, xfs_fileoff_t bno,
+               xfs_filblks_t len);
 int    xfs_bmap_add_attrfork(struct xfs_inode *ip, int size, int rsvd);
 void   xfs_bmap_local_to_extents_empty(struct xfs_inode *ip, int whichfork);
 void   xfs_bmap_add_free(struct xfs_mount *mp, struct xfs_defer_ops *dfops,