Btrfs: Avoid memcpy where possible in extent_buffers

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

1 files changed, 40 insertions, 5 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 30fbbd7221a9..aed08618aca6 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -483,15 +483,50 @@ static inline void btrfs_set_##name(struct extent_buffer *eb,		\
 #define BTRFS_SETGET_HEADER_FUNCS(name, type, member, bits)             \
 static inline u##bits btrfs_##name(struct extent_buffer *eb)            \
 {                                                                       \
-        __le##bits res;                                                 \
-        read_eb_member(eb, NULL, type, member, &res);                   \
-        return le##bits##_to_cpu(res);                                  \
+        int err;                                                        \
+        char *map_token;                                                \
+        char *kaddr;                                                    \
+        unsigned long map_start;                                        \
+        unsigned long map_len;                                          \
+        unsigned long offset = offsetof(type, member);                  \
+        err = map_extent_buffer(eb, offset,                             \
+                                sizeof(((type *)0)->member),            \
+                                &map_token, &kaddr,                     \
+                                &map_start, &map_len, KM_USER0);        \
+        if (!err) {                                                     \
+                __le##bits *tmp = (__le##bits *)(kaddr + offset -       \
+                                               map_start);              \
+                u##bits res = le##bits##_to_cpu(*tmp);                  \
+                unmap_extent_buffer(eb, map_token, KM_USER0);           \
+                return res;                                             \
+        } else {                                                        \
+                __le##bits res;                                         \
+                read_eb_member(eb, NULL, type, member, &res);           \
+                return le##bits##_to_cpu(res);                          \
+        }                                                               \
 }                                                                       \
 static inline void btrfs_set_##name(struct extent_buffer *eb,           \
                                     u##bits val)                        \
 {                                                                       \
-        val = cpu_to_le##bits(val);                                     \
-        write_eb_member(eb, NULL, type, member, &val);                  \
+        int err;                                                        \
+        char *map_token;                                                \
+        char *kaddr;                                                    \
+        unsigned long map_start;                                        \
+        unsigned long map_len;                                          \
+        unsigned long offset = offsetof(type, member);                  \
+        err = map_extent_buffer(eb, offset,                             \
+                                sizeof(((type *)0)->member),            \
+                                &map_token, &kaddr,                     \
+                                &map_start, &map_len, KM_USER0);        \
+        if (!err) {                                                     \
+                __le##bits *tmp = (__le##bits *)(kaddr + offset -       \
+                                               map_start);              \
+                *tmp = cpu_to_le##bits(val);                            \
+                unmap_extent_buffer(eb, map_token, KM_USER0);           \
+        } else {                                                        \
+                val = cpu_to_le##bits(val);                             \
+                write_eb_member(eb, NULL, type, member, &val);          \
+        }                                                               \
 }
 
 #define BTRFS_SETGET_STACK_FUNCS(name, type, member, bits)              \