xfs: move DIO mapping size calculation

The mapping size calculation is done last in __xfs_get_blocks(), but
we are going to need the actual mapping size we will use to map the
direct IO correctly in xfs_map_direct(). Factor out the calculation
for code clarity, and move the call to be the first operation in
mapping the extent to the returned buffer.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

1 files changed, 46 insertions, 33 deletions

diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index 489ed200bbbb..4a29399ed549 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -1249,6 +1249,47 @@ xfs_map_direct(
         }
 }
 
+
+/*
+ * If this is O_DIRECT or the mpage code calling tell them how large the mapping
+ * is, so that we can avoid repeated get_blocks calls.
+ *
+ * If the mapping spans EOF, then we have to break the mapping up as the mapping
+ * for blocks beyond EOF must be marked new so that sub block regions can be
+ * correctly zeroed. We can't do this for mappings within EOF unless the mapping
+ * was just allocated or is unwritten, otherwise the callers would overwrite
+ * existing data with zeros. Hence we have to split the mapping into a range up
+ * to and including EOF, and a second mapping for beyond EOF.
+ */
+static void
+xfs_map_trim_size(
+        struct inode            *inode,
+        sector_t                iblock,
+        struct buffer_head      *bh_result,
+        struct xfs_bmbt_irec    *imap,
+        xfs_off_t               offset,
+        ssize_t                 size)
+{
+        xfs_off_t               mapping_size;
+
+        mapping_size = imap->br_startoff + imap->br_blockcount - iblock;
+        mapping_size <<= inode->i_blkbits;
+
+        ASSERT(mapping_size > 0);
+        if (mapping_size > size)
+                mapping_size = size;
+        if (offset < i_size_read(inode) &&
+            offset + mapping_size >= i_size_read(inode)) {
+                /* limit mapping to block that spans EOF */
+                mapping_size = roundup_64(i_size_read(inode) - offset,
+                                          1 << inode->i_blkbits);
+        }
+        if (mapping_size > LONG_MAX)
+                mapping_size = LONG_MAX;
+
+        bh_result->b_size = mapping_size;
+}
+
 STATIC int
 __xfs_get_blocks(
         struct inode            *inode,
@@ -1347,6 +1388,11 @@ __xfs_get_blocks(
                 goto out_unlock;
         }
 
+        /* trim mapping down to size requested */
+        if (direct || size > (1 << inode->i_blkbits))
+                xfs_map_trim_size(inode, iblock, bh_result,
+                                  &imap, offset, size);
+
         /*
          * For unwritten extents do not report a disk address in the buffered
          * read case (treat as if we're reading into a hole).
@@ -1392,39 +1438,6 @@ __xfs_get_blocks(
                 }
         }
 
-        /*
-         * If this is O_DIRECT or the mpage code calling tell them how large
-         * the mapping is, so that we can avoid repeated get_blocks calls.
-         *
-         * If the mapping spans EOF, then we have to break the mapping up as the
-         * mapping for blocks beyond EOF must be marked new so that sub block
-         * regions can be correctly zeroed. We can't do this for mappings within
-         * EOF unless the mapping was just allocated or is unwritten, otherwise
-         * the callers would overwrite existing data with zeros. Hence we have
-         * to split the mapping into a range up to and including EOF, and a
-         * second mapping for beyond EOF.
-         */
-        if (direct || size > (1 << inode->i_blkbits)) {
-                xfs_off_t               mapping_size;
-
-                mapping_size = imap.br_startoff + imap.br_blockcount - iblock;
-                mapping_size <<= inode->i_blkbits;
-
-                ASSERT(mapping_size > 0);
-                if (mapping_size > size)
-                        mapping_size = size;
-                if (offset < i_size_read(inode) &&
-                    offset + mapping_size >= i_size_read(inode)) {
-                        /* limit mapping to block that spans EOF */
-                        mapping_size = roundup_64(i_size_read(inode) - offset,
-                                                  1 << inode->i_blkbits);
-                }
-                if (mapping_size > LONG_MAX)
-                        mapping_size = LONG_MAX;
-
-                bh_result->b_size = mapping_size;
-        }
-
         return 0;
 
 out_unlock: