libext2fs: Avoid creating unneeded new extents in ext2fs_extent_set_bmap()

Avoiding inserting a new extent if it is possible to merge the new
block to the beginning or the end of the previous or next extent.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/lib/ext2fs/extent.c b/lib/ext2fs/extent.c
index c47fbcc..1505447 100644 (file)
--- a/lib/ext2fs/extent.c
+++ b/lib/ext2fs/extent.c
@@ -1146,11 +1146,14 @@ errcode_t ext2fs_extent_set_bmap(ext2_extent_handle_t handle,
        int                     mapped = 1; /* logical is mapped? */
        int                     orig_height;
        int                     extent_uninit = 0;
+       int                     prev_uninit = 0;
+       int                     next_uninit = 0;
        int                     new_uninit = 0;
        int                     max_len = EXT_INIT_MAX_LEN;
+       int                     has_prev, has_next;
        blk64_t                 orig_lblk;
        struct extent_path      *path;
-       struct ext2fs_extent    extent;
+       struct ext2fs_extent    extent, next_extent, prev_extent;
        struct ext2fs_extent    newextent;
        struct ext2_extent_info info;
 
@@ -1222,12 +1225,44 @@ errcode_t ext2fs_extent_set_bmap(ext2_extent_handle_t handle,
        /*
         * This may be the extent *before* the requested logical,
         * if it's currently unmapped.
+        *
+        * Get the previous and next leaf extents, if they are present.
         */
        retval = ext2fs_extent_get(handle, EXT2_EXTENT_CURRENT, &extent);
        if (retval)
                goto done;
        if (extent.e_flags & EXT2_EXTENT_FLAGS_UNINIT)
                extent_uninit = 1;
+       retval = ext2fs_extent_get(handle, EXT2_EXTENT_NEXT_LEAF, &next_extent);
+       if (retval) {
+               has_next = 0;
+               if (retval != EXT2_ET_EXTENT_NO_NEXT)
+                       goto done;
+       } else {
+               dbg_print_extent("set_bmap: next_extent",
+                                &next_extent);
+               has_next = 1;
+               if (next_extent.e_flags & EXT2_EXTENT_FLAGS_UNINIT)
+                       next_uninit = 1;
+       }
+       retval = ext2fs_extent_goto(handle, logical);
+       if (retval && retval != EXT2_ET_EXTENT_NOT_FOUND)
+               goto done;
+       retval = ext2fs_extent_get(handle, EXT2_EXTENT_PREV_LEAF, &prev_extent);
+       if (retval) {
+               has_prev = 0;
+               if (retval != EXT2_ET_EXTENT_NO_PREV)
+                       goto done;
+       } else {
+               has_prev = 1;
+               dbg_print_extent("set_bmap: prev_extent",
+                                &prev_extent);
+               if (prev_extent.e_flags & EXT2_EXTENT_FLAGS_UNINIT)
+                       prev_uninit = 1;
+       }
+       retval = ext2fs_extent_goto(handle, logical);
+       if (retval && retval != EXT2_ET_EXTENT_NOT_FOUND)
+               goto done;
 
        /* check if already pointing to the requested physical */
        if (mapped && (new_uninit == extent_uninit) &&
@@ -1248,6 +1283,28 @@ errcode_t ext2fs_extent_set_bmap(ext2_extent_handle_t handle,
                    ((int) extent.e_len < max_len-1)) {
                        extent.e_len++;
                        retval = ext2fs_extent_replace(handle, 0, &extent);
+               } else if ((logical == extent.e_lblk - 1) &&
+                          (physical == extent.e_pblk - 1) &&
+                          (new_uninit == extent_uninit) &&
+                          ((int) extent.e_len < max_len - 1)) {
+                       extent.e_len++;
+                       extent.e_lblk--;
+                       extent.e_pblk--;
+                       retval = ext2fs_extent_replace(handle, 0, &extent);
+               } else if (has_next &&
+                          (logical == next_extent.e_lblk - 1) &&
+                          (physical == next_extent.e_pblk - 1) &&
+                          (new_uninit == next_uninit) &&
+                          ((int) next_extent.e_len < max_len - 1)) {
+                       retval = ext2fs_extent_get(handle,
+                                                  EXT2_EXTENT_NEXT_LEAF,
+                                                  &next_extent);
+                       if (retval)
+                               goto done;
+                       next_extent.e_len++;
+                       next_extent.e_lblk--;
+                       next_extent.e_pblk--;
+                       retval = ext2fs_extent_replace(handle, 0, &next_extent);
                } else if (logical < extent.e_lblk)
                        retval = ext2fs_extent_insert(handle, 0, &newextent);
                else
@@ -1279,14 +1336,32 @@ errcode_t ext2fs_extent_set_bmap(ext2_extent_handle_t handle,
 #ifdef DEBUG
                printf("(re/un)mapping last block in extent\n");
 #endif
-               /* Make sure insert works before replacing old extent */
                if (physical) {
-                       retval = ext2fs_extent_insert(handle,
-                                       EXT2_EXTENT_INSERT_AFTER, &newextent);
+                       if (has_next &&
+                           (logical == (next_extent.e_lblk - 1)) &&
+                           (physical == (next_extent.e_pblk - 1)) &&
+                           (new_uninit == next_uninit) &&
+                           ((int) next_extent.e_len < max_len - 1)) {
+                               retval = ext2fs_extent_get(handle,
+                                       EXT2_EXTENT_NEXT_LEAF, &next_extent);
+                               if (retval)
+                                       goto done;
+                               next_extent.e_len++;
+                               next_extent.e_lblk--;
+                               next_extent.e_pblk--;
+                               retval = ext2fs_extent_replace(handle, 0,
+                                                              &next_extent);
+                               if (retval)
+                                       goto done;
+                       } else
+                               retval = ext2fs_extent_insert(handle,
+                                     EXT2_EXTENT_INSERT_AFTER, &newextent);
                        if (retval)
                                goto done;
                        /* Now pointing at inserted extent; move back to prev */
-                       retval = ext2fs_extent_goto(handle, logical - 1);
+                       retval = ext2fs_extent_get(handle,
+                                                  EXT2_EXTENT_PREV_LEAF,
+                                                  &extent);
                        if (retval)
                                goto done;
                }
@@ -1299,30 +1374,23 @@ errcode_t ext2fs_extent_set_bmap(ext2_extent_handle_t handle,
                printf("(re/un)mapping first block in extent\n");
 #endif
                if (physical) {
-                       retval = ext2fs_extent_get(handle, 
-                                                  EXT2_EXTENT_PREV_LEAF,
-                                                  &extent);
-                       if (extent.e_flags & EXT2_EXTENT_FLAGS_UNINIT)
-                               extent_uninit = 1;
-                       if (retval == EXT2_ET_EXTENT_NO_PREV) {
-                               retval = ext2fs_extent_goto(handle, logical);
+                       if (has_prev &&
+                           (logical == (prev_extent.e_lblk +
+                                        prev_extent.e_len)) &&
+                           (physical == (prev_extent.e_pblk +
+                                         prev_extent.e_len)) &&
+                           (new_uninit == prev_uninit) &&
+                           ((int) prev_extent.e_len < max_len-1)) {
+                               retval = ext2fs_extent_get(handle, 
+                                       EXT2_EXTENT_PREV_LEAF, &prev_extent);
                                if (retval)
                                        goto done;
-                               retval = ext2fs_extent_insert(handle,
-                                                             0, &newextent);
-                       } else if (retval)
-                               goto done;
-                       else if ((logical == extent.e_lblk + extent.e_len) &&
-                                (physical == extent.e_pblk + extent.e_len) &&
-                                (new_uninit == extent_uninit) &&
-                                ((int) extent.e_len < max_len-1)) {
-                               extent.e_len++;
+                               prev_extent.e_len++;
                                retval = ext2fs_extent_replace(handle, 0,
-                                                              &extent);
-                       } else {
+                                                              &prev_extent);
+                       } else
                                retval = ext2fs_extent_insert(handle,
-                                     EXT2_EXTENT_INSERT_AFTER, &newextent);
-                       }
+                                                             0, &newextent);
                        if (retval)
                                goto done;
                        retval = ext2fs_extent_get(handle,