Changeset d241aae in mainline for uspace/lib/ext2/libext2_superblock.c

Timestamp:

2011-02-15T19:24:38Z (14 years ago)

Author:

Martin Sucha <sucha14@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

ce13577

Parents:

1d6f507

Message:

Add support for reading ext2 block group descriptors

File:

• uspace/lib/ext2/libext2_superblock.c (modified) (1 diff)

uspace/lib/ext2/libext2_superblock.c

@@ -260 +260 @@
  * Compute count of block groups present in the filesystem
  * 
+ * Note: This function works only for correct filesystem,
+ *       i.e. it assumes that total block count > 0 and
+ *       blocks per group > 0
+ * 
+ * Example:
+ *   If there are 3 blocks per group, the result should be as follows:
+ *   Total blocks       Result
+ *   1                          1
+ *   2                          1
+ *   3                          1
+ *   4                          2
+ * 
+ * 
  * @param sb pointer to superblock
  */
 inline uint32_t ext2_superblock_get_block_group_count(ext2_superblock_t *sb)
 {
-        return ext2_superblock_get_total_block_count(sb) / 
-            ext2_superblock_get_blocks_per_group(sb);
+        /* We add one to the result because e.g. 2/3 = 0, while to store
+         *  2 blocks in 3-block group we need one (1) block group
+         * 
+         * We subtract one first because of special case that to store e.g.
+         *  3 blocks in a 3-block group we need only one group
+         *  (and 3/3 yields one - this is one more that we want as we
+         *   already add one at the end)
+         */ 
+        return ((ext2_superblock_get_total_block_count(sb)-1) / 
+            ext2_superblock_get_blocks_per_group(sb))+1;
 }