Change on-disk format to support 2^15 uninitialized extents

This change was suggested by Andreas Dilger. 
This patch changes the EXT_MAX_LEN value and extent code which marks/checks
uninitialized extents. With this change it will be possible to have
initialized extents with 2^15 blocks (earlier the max blocks we could have
was 2^15 - 1). This way we can have better extent-to-block alignment.
Now, maximum number of blocks we can have in an initialized extent is 2^15
and in an uninitialized extent is 2^15 - 1.

Signed-off-by: Amit Arora <aarora@in.ibm.com>

1 files changed, 25 insertions, 3 deletions

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index ded3d469f978..77146b826a13 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -1107,7 +1107,7 @@ static int
 ext4_can_extents_be_merged(struct inode *inode, struct ext4_extent *ex1,
                                 struct ext4_extent *ex2)
 {
-        unsigned short ext1_ee_len, ext2_ee_len;
+        unsigned short ext1_ee_len, ext2_ee_len, max_len;
 
         /*
          * Make sure that either both extents are uninitialized, or
@@ -1116,6 +1116,11 @@ ext4_can_extents_be_merged(struct inode *inode, struct ext4_extent *ex1,
         if (ext4_ext_is_uninitialized(ex1) ^ ext4_ext_is_uninitialized(ex2))
                 return 0;
 
+        if (ext4_ext_is_uninitialized(ex1))
+                max_len = EXT_UNINIT_MAX_LEN;
+        else
+                max_len = EXT_INIT_MAX_LEN;
+
         ext1_ee_len = ext4_ext_get_actual_len(ex1);
         ext2_ee_len = ext4_ext_get_actual_len(ex2);
 
@@ -1128,7 +1133,7 @@ ext4_can_extents_be_merged(struct inode *inode, struct ext4_extent *ex1,
          * as an RO_COMPAT feature, refuse to merge to extents if
          * this can result in the top bit of ee_len being set.
          */
-        if (ext1_ee_len + ext2_ee_len > EXT_MAX_LEN)
+        if (ext1_ee_len + ext2_ee_len > max_len)
                 return 0;
 #ifdef AGGRESSIVE_TEST
         if (le16_to_cpu(ex1->ee_len) >= 4)
@@ -1815,7 +1820,11 @@ ext4_ext_rm_leaf(handle_t *handle, struct inode *inode,
 
                 ex->ee_block = cpu_to_le32(block);
                 ex->ee_len = cpu_to_le16(num);
-                if (uninitialized)
+                /*
+                 * Do not mark uninitialized if all the blocks in the
+                 * extent have been removed.
+                 */
+                if (uninitialized && num)
                         ext4_ext_mark_uninitialized(ex);
 
                 err = ext4_ext_dirty(handle, inode, path + depth);
@@ -2308,6 +2317,19 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
         /* allocate new block */
         goal = ext4_ext_find_goal(inode, path, iblock);
 
+        /*
+         * See if request is beyond maximum number of blocks we can have in
+         * a single extent. For an initialized extent this limit is
+         * EXT_INIT_MAX_LEN and for an uninitialized extent this limit is
+         * EXT_UNINIT_MAX_LEN.
+         */
+        if (max_blocks > EXT_INIT_MAX_LEN &&
+            create != EXT4_CREATE_UNINITIALIZED_EXT)
+                max_blocks = EXT_INIT_MAX_LEN;
+        else if (max_blocks > EXT_UNINIT_MAX_LEN &&
+                 create == EXT4_CREATE_UNINITIALIZED_EXT)
+                max_blocks = EXT_UNINIT_MAX_LEN;
+
         /* Check if we can really insert (iblock)::(iblock+max_blocks) extent */
         newex.ee_block = cpu_to_le32(iblock);
         newex.ee_len = cpu_to_le16(max_blocks);