Btrfs: Optimizations for the extent_buffer code

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 8 insertions, 3 deletions

diff --git a/fs/btrfs/extent_map.c b/fs/btrfs/extent_map.c
index 55fefdfab84c..8bef309e1b37 100644
--- a/fs/btrfs/extent_map.c
+++ b/fs/btrfs/extent_map.c
@@ -2140,14 +2140,20 @@ void read_extent_buffer(struct extent_buffer *eb, void *dstv,
 EXPORT_SYMBOL(read_extent_buffer);
 
 int map_extent_buffer(struct extent_buffer *eb, unsigned long start,
+                      unsigned long min_len,
                       char **token, char **map,
                       unsigned long *map_start,
                       unsigned long *map_len, int km)
 {
-        size_t offset;
+        size_t offset = start & (PAGE_CACHE_SIZE - 1);
         char *kaddr;
         size_t start_offset = eb->start & ((u64)PAGE_CACHE_SIZE - 1);
         unsigned long i = (start_offset + start) >> PAGE_CACHE_SHIFT;
+        unsigned long end_i = (start_offset + start + min_len) >>
+                                PAGE_CACHE_SHIFT;
+
+        if (i != end_i)
+                return -EINVAL;
 
         WARN_ON(start > eb->len);
 
@@ -2155,8 +2161,7 @@ int map_extent_buffer(struct extent_buffer *eb, unsigned long start,
                 offset = start_offset;
                 *map_start = 0;
         } else {
-                offset = 0;
-                *map_start = (i << PAGE_CACHE_SHIFT) - offset;
+                *map_start = (i << PAGE_CACHE_SHIFT) - start_offset;
         }
 
         // kaddr = kmap_atomic(eb->pages[i], km);