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

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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>
This commit is contained in:
Amit Arora
2007-07-18 09:02:56 -04:00
committed by Theodore Ts'o
parent 56055d3ae4
commit 749269faca
2 changed files with 52 additions and 7 deletions
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31
include/linux/ext4_fs_extents.h
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@@ -141,7 +141,25 @@ typedef int (*ext_prepare_callback)(struct inode *, struct ext4_ext_path *,
#define EXT_MAX_BLOCK 0xffffffff
#define EXT_MAX_LEN ((1UL << 15) - 1)
/*
* EXT_INIT_MAX_LEN is the maximum number of blocks we can have in an
* initialized extent. This is 2^15 and not (2^16 - 1), since we use the
* MSB of ee_len field in the extent datastructure to signify if this
* particular extent is an initialized extent or an uninitialized (i.e.
* preallocated).
* EXT_UNINIT_MAX_LEN is the maximum number of blocks we can have in an
* uninitialized extent.
* If ee_len is <= 0x8000, it is an initialized extent. Otherwise, it is an
* uninitialized one. In other words, if MSB of ee_len is set, it is an
* uninitialized extent with only one special scenario when ee_len = 0x8000.
* In this case we can not have an uninitialized extent of zero length and
* thus we make it as a special case of initialized extent with 0x8000 length.
* This way we get better extent-to-group alignment for initialized extents.
* Hence, the maximum number of blocks we can have in an *initialized*
* extent is 2^15 (32768) and in an *uninitialized* extent is 2^15-1 (32767).
*/
#define EXT_INIT_MAX_LEN (1UL << 15)
#define EXT_UNINIT_MAX_LEN (EXT_INIT_MAX_LEN - 1)
#define EXT_FIRST_EXTENT(__hdr__) \
@@ -190,17 +208,22 @@ ext4_ext_invalidate_cache(struct inode *inode)
static inline void ext4_ext_mark_uninitialized(struct ext4_extent *ext)
{
ext->ee_len |= cpu_to_le16(0x8000);
/* We can not have an uninitialized extent of zero length! */
BUG_ON((le16_to_cpu(ext->ee_len) & ~EXT_INIT_MAX_LEN) == 0);
ext->ee_len |= cpu_to_le16(EXT_INIT_MAX_LEN);
}
static inline int ext4_ext_is_uninitialized(struct ext4_extent *ext)
{
return (int)(le16_to_cpu((ext)->ee_len) & 0x8000);
/* Extent with ee_len of 0x8000 is treated as an initialized extent */
return (le16_to_cpu(ext->ee_len) > EXT_INIT_MAX_LEN);
}
static inline int ext4_ext_get_actual_len(struct ext4_extent *ext)
{
return (int)(le16_to_cpu((ext)->ee_len) & 0x7FFF);
return (le16_to_cpu(ext->ee_len) <= EXT_INIT_MAX_LEN ?
le16_to_cpu(ext->ee_len) :
(le16_to_cpu(ext->ee_len) - EXT_INIT_MAX_LEN));
}
extern int ext4_extent_tree_init(handle_t *, struct inode *);