[GFS2] Add a function to interate over an extent

This adds a function (currently the only use is during mapping
of already allocated blocks, but watch this space) which iterates
over a number of pointers in a block and returns the extent length.

If the initial pointer is 0 (i.e. unallocated) it will return the
number of unallocated blocks in the extent. If the initial pointer
is allocated, then it returns the number of contiguously allocated
blocks in the extent.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

1 files changed, 52 insertions, 16 deletions

diff --git a/fs/gfs2/bmap.c b/fs/gfs2/bmap.c
index 7f72564e0597..6780aa5841b2 100644
--- a/fs/gfs2/bmap.c
+++ b/fs/gfs2/bmap.c
@@ -422,6 +422,42 @@ static void release_metapath(struct metapath *mp)
                         brelse(mp->mp_bh[i]);
 }
 
+/**
+ * gfs2_extent_length - Returns length of an extent of blocks
+ * @start: Start of the buffer
+ * @len: Length of the buffer in bytes
+ * @ptr: Current position in the buffer
+ * @limit: Max extent length to return (0 = unlimited)
+ * @eob: Set to 1 if we hit "end of block"
+ *
+ * If the first block is zero (unallocated) it will return the number of
+ * unallocated blocks in the extent, otherwise it will return the number
+ * of contiguous blocks in the extent.
+ *
+ * Returns: The length of the extent (minimum of one block)
+ */
+
+static inline unsigned int gfs2_extent_length(void *start, unsigned int len, __be64 *ptr, unsigned limit, int *eob)
+{
+        const __be64 *end = (start + len);
+        const __be64 *first = ptr;
+        u64 d = be64_to_cpu(*ptr);
+
+        *eob = 0;
+        do {
+                ptr++;
+                if (ptr >= end)
+                        break;
+                if (limit && --limit == 0)
+                        break;
+                if (d)
+                        d++;
+        } while(be64_to_cpu(*ptr) == d);
+        if (ptr >= end)
+                *eob = 1;
+        return (ptr - first);
+}
+
 static inline void bmap_lock(struct inode *inode, int create)
 {
         struct gfs2_inode *ip = GFS2_I(inode);
@@ -499,26 +535,26 @@ int gfs2_block_map(struct inode *inode, sector_t lblock,
                 goto out_fail;
         boundary = error;
 
+        if (new) {
+                map_bh(bh_map, inode->i_sb, dblock);
+                if (boundary)
+                        set_buffer_boundary(bh_map);
+                gfs2_trans_add_bh(ip->i_gl, mp.mp_bh[0], 1);
+                gfs2_dinode_out(ip, mp.mp_bh[0]->b_data);
+                set_buffer_new(bh_map);
+                goto out_ok;
+        }
+
         if (dblock) {
+                unsigned int len;
+                struct buffer_head *bh = mp.mp_bh[ip->i_height - 1];
+                __be64 *ptr = metapointer(&boundary, ip->i_height - 1, &mp);
                 map_bh(bh_map, inode->i_sb, dblock);
+                len = gfs2_extent_length(bh->b_data, bh->b_size, ptr, maxlen,
+                                         &boundary);
+                bh_map->b_size = (len << inode->i_blkbits);
                 if (boundary)
                         set_buffer_boundary(bh_map);
-                if (new) {
-                        gfs2_trans_add_bh(ip->i_gl, mp.mp_bh[0], 1);
-                        gfs2_dinode_out(ip, mp.mp_bh[0]->b_data);
-                        set_buffer_new(bh_map);
-                        goto out_ok;
-                }
-                while(--maxlen && !buffer_boundary(bh_map)) {
-                        u64 eblock;
-                        mp.mp_list[ip->i_height - 1]++;
-                        boundary = lookup_block(ip, ip->i_height - 1, &mp, 0, &new, &eblock);
-                        if (eblock != ++dblock)
-                                break;
-                        bh_map->b_size += (1 << inode->i_blkbits);
-                        if (boundary)
-                                set_buffer_boundary(bh_map);
-                }
         }
 out_ok:
         error = 0;