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[PATCH] ext4: uninitialised extent handling 

Make it possible to add file preallocation support in future as an RO_COMPAT
feature by recognizing uninitialized extents as holes and limiting extent
length to keep the top bit of ee_len free for marking uninitialized extents.

Signed-off-by: Suparna Bhattacharya <suparna@in.ibm.com>
Signed-off-by: Mingming Cao <cmm@us.ibm.com>
Signed-off-by: Dave Kleikamp <shaggy@austin.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Suparna Bhattacharya 2006-10-11 01:21:06 -07:00 committed by Linus Torvalds
parent f65e6fba16
commit 471d4011a9
2 changed files with 18 additions and 0 deletions
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16
fs/ext4/extents.c
View File

@ -1082,6 +1082,13 @@ ext4_can_extents_be_merged(struct inode *inode, struct ext4_extent *ex1,
!= le32_to_cpu(ex2->ee_block))
return 0;
/*
* To allow future support for preallocated extents to be added
* as an RO_COMPAT feature, refuse to merge to extents if
* can result in the top bit of ee_len being set
*/
if (le16_to_cpu(ex1->ee_len) + le16_to_cpu(ex2->ee_len) > EXT_MAX_LEN)
return 0;
#ifdef AGRESSIVE_TEST
if (le16_to_cpu(ex1->ee_len) >= 4)
return 0;
@ -1944,6 +1951,15 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
unsigned long ee_block = le32_to_cpu(ex->ee_block);
ext4_fsblk_t ee_start = ext_pblock(ex);
unsigned short ee_len = le16_to_cpu(ex->ee_len);
/*
* Allow future support for preallocated extents to be added
* as an RO_COMPAT feature:
* Uninitialized extents are treated as holes, except that
* we avoid (fail) allocating new blocks during a write.
*/
if (ee_len > EXT_MAX_LEN)
goto out2;
/* if found exent covers block, simple return it */
if (iblock >= ee_block && iblock < ee_block + ee_len) {
newblock = iblock - ee_block + ee_start;

2
include/linux/ext4_fs_extents.h
View File

@ -141,6 +141,8 @@ typedef int (*ext_prepare_callback)(struct inode *, struct ext4_ext_path *,
#define EXT_MAX_BLOCK 0xffffffff
#define EXT_MAX_LEN ((1UL << 15) - 1)
#define EXT_FIRST_EXTENT(__hdr__) \
((struct ext4_extent *) (((char *) (__hdr__)) + \