When meta_bg feature is enabled and s_first_meta_bg != 0,
ext4_init_block_bitmap() miscalculates the number of block used by
the group descriptor table (0 or 1 for metablock block group)
This patch fix it by using ext4_bg_num_gdb()
Signed-off-by: Akinobu Mita <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Stephen Tweedie <[email protected]>
Cc: [email protected]
Cc: Mingming Cao <[email protected]>
Cc: Theodore Tso <[email protected]>
---
fs/ext4/balloc.c | 7 +------
1 file changed, 1 insertion(+), 6 deletions(-)
Index: 2.6-git/fs/ext4/balloc.c
===================================================================
--- 2.6-git.orig/fs/ext4/balloc.c
+++ 2.6-git/fs/ext4/balloc.c
@@ -121,12 +121,7 @@ unsigned ext4_init_block_bitmap(struct s
le16_to_cpu(sbi->s_es->s_reserved_gdt_blocks);
}
} else { /* For META_BG_BLOCK_GROUPS */
- int group_rel = (block_group -
- le32_to_cpu(sbi->s_es->s_first_meta_bg)) %
- EXT4_DESC_PER_BLOCK(sb);
- if (group_rel == 0 || group_rel == 1 ||
- (group_rel == EXT4_DESC_PER_BLOCK(sb) - 1))
- bit_max += 1;
+ bit_max += ext4_bg_num_gdb(sb, block_group);
}
if (block_group == sbi->s_groups_count - 1) {
On Jun 15, 2008 23:24 +0900, Akinobu Mita wrote:
> When meta_bg feature is enabled and s_first_meta_bg != 0,
> ext4_init_block_bitmap() miscalculates the number of block used by
> the group descriptor table (0 or 1 for metablock block group)
Can you please clarify why the calculation is incorrect? I admit that
I didn't test with META_BG enabled, so it could well be wrong, but looking
at the code I can't understand why it is incorrect.
> @@ -121,12 +121,7 @@ unsigned ext4_init_block_bitmap(struct s
if (!EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_META_BG) ||
block_group < le32_to_cpu(sbi->s_es->s_first_meta_bg) *
sbi->s_desc_per_block) {
if (bit_max) {
bit_max += ext4_bg_num_gdb(sb, block_group);
bit_max +=
> le16_to_cpu(sbi->s_es->s_reserved_gdt_blocks);
> }
> } else { /* For META_BG_BLOCK_GROUPS */
> - int group_rel = (block_group -
> - le32_to_cpu(sbi->s_es->s_first_meta_bg)) %
> - EXT4_DESC_PER_BLOCK(sb);
> - if (group_rel == 0 || group_rel == 1 ||
> - (group_rel == EXT4_DESC_PER_BLOCK(sb) - 1))
> - bit_max += 1;
> + bit_max += ext4_bg_num_gdb(sb, block_group);
> }
As you can see, the "if" checks if the block group is before s_first_meta_bg
to treat it as a "normal" group, and only uses the "else" once beyond the
start of the s_first_meta_bg limit.
It definitely is less complex to use ext4_bg_num_gdb(), and this could
further be simplified by using ext4_bg_gdb_meta() in the "else" clause.
In fact, the whole if/else could be replaced with ext4_bg_num_gdb() if
it weren't for s_reserved_gdt_blocks.
Maybe it makes sense (cleaner code, less chance for bugs) to change the
ext4_bg_num_gdb() function to take a parameter on whether it should
include the s_reserved_gdt_blocks or not:
static unsigned long ext4_bg_num_gdb_nometa(struct super_block *sb, int group,
int reserved)
{
if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
EXT4_FEATURE_RO_COMPAT_SPARSE_SUPER) &&
!ext4_group_sparse(group))
return 0;
return EXT4_SB(sb)->s_gdb_count +
reserved ? EXT4_SB(sb)->s_reserved_gdt_blocks : 0;
}
unsigned long ext4_bg_num_gdb(struct super_block *sb, int group, int reserved)
{
unsigned long first_meta_bg =
le32_to_cpu(EXT4_SB(sb)->s_es->s_first_meta_bg);
unsigned long metagroup = group / EXT4_DESC_PER_BLOCK(sb);
if (!EXT4_HAS_INCOMPAT_FEATURE(sb,EXT4_FEATURE_INCOMPAT_META_BG) ||
metagroup < first_meta_bg)
return ext4_bg_num_gdb_nometa(sb, group, reserved);
return ext4_bg_num_gdb_meta(sb, group);
}
The fewer places in the code that need to understand META_BG, the less
chance of having a bug. Now the code in ext4_init_block_bitmap() can be:
bit_max += ext4_bg_num_gdb(sb, block_group, 1);
Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.
On Sun, Jun 15, 2008 at 11:19:00PM -0600, Andreas Dilger wrote:
> On Jun 15, 2008 23:24 +0900, Akinobu Mita wrote:
> > When meta_bg feature is enabled and s_first_meta_bg != 0,
> > ext4_init_block_bitmap() miscalculates the number of block used by
> > the group descriptor table (0 or 1 for metablock block group)
>
> Can you please clarify why the calculation is incorrect? I admit that
> I didn't test with META_BG enabled, so it could well be wrong, but looking
> at the code I can't understand why it is incorrect.
group_rel in the original code should be calculated by:
group_rel = block_group % EXT4_DESC_PER_BLOCK(sb);
No need to subtract s_first_meta_bg from brock_group.
It will be equivalent what ext4_bg_num_gdb_meta() does
> > @@ -121,12 +121,7 @@ unsigned ext4_init_block_bitmap(struct s
> if (!EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_META_BG) ||
> block_group < le32_to_cpu(sbi->s_es->s_first_meta_bg) *
> sbi->s_desc_per_block) {
> if (bit_max) {
> bit_max += ext4_bg_num_gdb(sb, block_group);
> bit_max +=
> > le16_to_cpu(sbi->s_es->s_reserved_gdt_blocks);
> > }
> > } else { /* For META_BG_BLOCK_GROUPS */
> > - int group_rel = (block_group -
> > - le32_to_cpu(sbi->s_es->s_first_meta_bg)) %
> > - EXT4_DESC_PER_BLOCK(sb);
> > - if (group_rel == 0 || group_rel == 1 ||
> > - (group_rel == EXT4_DESC_PER_BLOCK(sb) - 1))
> > - bit_max += 1;
> > + bit_max += ext4_bg_num_gdb(sb, block_group);
> > }
>
> As you can see, the "if" checks if the block group is before s_first_meta_bg
> to treat it as a "normal" group, and only uses the "else" once beyond the
> start of the s_first_meta_bg limit.
>
> It definitely is less complex to use ext4_bg_num_gdb(), and this could
> further be simplified by using ext4_bg_gdb_meta() in the "else" clause.
> In fact, the whole if/else could be replaced with ext4_bg_num_gdb() if
> it weren't for s_reserved_gdt_blocks.
>
> Maybe it makes sense (cleaner code, less chance for bugs) to change the
> ext4_bg_num_gdb() function to take a parameter on whether it should
> include the s_reserved_gdt_blocks or not:
>
> static unsigned long ext4_bg_num_gdb_nometa(struct super_block *sb, int group,
> int reserved)
> {
> if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
> EXT4_FEATURE_RO_COMPAT_SPARSE_SUPER) &&
> !ext4_group_sparse(group))
> return 0;
> return EXT4_SB(sb)->s_gdb_count +
> reserved ? EXT4_SB(sb)->s_reserved_gdt_blocks : 0;
> }
>
> unsigned long ext4_bg_num_gdb(struct super_block *sb, int group, int reserved)
> {
> unsigned long first_meta_bg =
> le32_to_cpu(EXT4_SB(sb)->s_es->s_first_meta_bg);
> unsigned long metagroup = group / EXT4_DESC_PER_BLOCK(sb);
>
> if (!EXT4_HAS_INCOMPAT_FEATURE(sb,EXT4_FEATURE_INCOMPAT_META_BG) ||
> metagroup < first_meta_bg)
> return ext4_bg_num_gdb_nometa(sb, group, reserved);
>
> return ext4_bg_num_gdb_meta(sb, group);
> }
>
> The fewer places in the code that need to understand META_BG, the less
> chance of having a bug. Now the code in ext4_init_block_bitmap() can be:
>
> bit_max += ext4_bg_num_gdb(sb, block_group, 1);
Looks good to me. But I'd like to divide into the change into simple
bugfix and cleanup patch in order to clarify the each change.
Here is a bugfix only patch.
From: Akinobu Mita <[email protected]>
Subject: ext4: fix ext4_init_block_bitmap() for metablock block group
When meta_bg feature is enabled and s_first_meta_bg != 0,
ext4_init_block_bitmap() miscalculates the number of block used by
the group descriptor table (0 or 1 for metablock block group)
group_rel in the original code should be calculated by:
group_rel = block_group % EXT4_DESC_PER_BLOCK(sb);
No need to subtract s_first_meta_bg from brock_group.
It will be equivalent what ext4_bg_num_gdb_meta() does
Signed-off-by: Akinobu Mita <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Stephen Tweedie <[email protected]>
Cc: [email protected]
Cc: Mingming Cao <[email protected]>
Cc: Theodore Tso <[email protected]>
---
fs/ext4/balloc.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
Index: 2.6-git/fs/ext4/balloc.c
===================================================================
--- 2.6-git.orig/fs/ext4/balloc.c
+++ 2.6-git/fs/ext4/balloc.c
@@ -121,9 +121,8 @@ unsigned ext4_init_block_bitmap(struct s
le16_to_cpu(sbi->s_es->s_reserved_gdt_blocks);
}
} else { /* For META_BG_BLOCK_GROUPS */
- int group_rel = (block_group -
- le32_to_cpu(sbi->s_es->s_first_meta_bg)) %
- EXT4_DESC_PER_BLOCK(sb);
+ int group_rel = block_group % EXT4_DESC_PER_BLOCK(sb);
+
if (group_rel == 0 || group_rel == 1 ||
(group_rel == EXT4_DESC_PER_BLOCK(sb) - 1))
bit_max += 1;
On Jun 16, 2008 23:10 +0900, Akinobu Mita wrote:
> Looks good to me. But I'd like to divide into the change into simple
> bugfix and cleanup patch in order to clarify the each change.
>
> Here is a bugfix only patch.
>
> From: Akinobu Mita <[email protected]>
> Subject: ext4: fix ext4_init_block_bitmap() for metablock block group
>
> When meta_bg feature is enabled and s_first_meta_bg != 0,
> ext4_init_block_bitmap() miscalculates the number of block used by
> the group descriptor table (0 or 1 for metablock block group)
>
> group_rel in the original code should be calculated by:
>
> group_rel = block_group % EXT4_DESC_PER_BLOCK(sb);
>
> No need to subtract s_first_meta_bg from brock_group.
> It will be equivalent what ext4_bg_num_gdb_meta() does
>
> Signed-off-by: Akinobu Mita <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Cc: Stephen Tweedie <[email protected]>
> Cc: [email protected]
> Cc: Mingming Cao <[email protected]>
> Cc: Theodore Tso <[email protected]>
Acked-by: Andreas Dilger <[email protected]>
> ---
> fs/ext4/balloc.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> Index: 2.6-git/fs/ext4/balloc.c
> ===================================================================
> --- 2.6-git.orig/fs/ext4/balloc.c
> +++ 2.6-git/fs/ext4/balloc.c
> @@ -121,9 +121,8 @@ unsigned ext4_init_block_bitmap(struct s
> le16_to_cpu(sbi->s_es->s_reserved_gdt_blocks);
> }
> } else { /* For META_BG_BLOCK_GROUPS */
> - int group_rel = (block_group -
> - le32_to_cpu(sbi->s_es->s_first_meta_bg)) %
> - EXT4_DESC_PER_BLOCK(sb);
> + int group_rel = block_group % EXT4_DESC_PER_BLOCK(sb);
> +
> if (group_rel == 0 || group_rel == 1 ||
> (group_rel == EXT4_DESC_PER_BLOCK(sb) - 1))
> bit_max += 1;
Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.
On Mon, 2008-06-16 at 13:19 -0600, Andreas Dilger wrote:
> On Jun 16, 2008 23:10 +0900, Akinobu Mita wrote:
> > Looks good to me. But I'd like to divide into the change into simple
> > bugfix and cleanup patch in order to clarify the each change.
> >
> > Here is a bugfix only patch.
> >
> > From: Akinobu Mita <[email protected]>
> > Subject: ext4: fix ext4_init_block_bitmap() for metablock block group
> >
> > When meta_bg feature is enabled and s_first_meta_bg != 0,
> > ext4_init_block_bitmap() miscalculates the number of block used by
> > the group descriptor table (0 or 1 for metablock block group)
> >
> > group_rel in the original code should be calculated by:
> >
> > group_rel = block_group % EXT4_DESC_PER_BLOCK(sb);
> >
> > No need to subtract s_first_meta_bg from brock_group.
> > It will be equivalent what ext4_bg_num_gdb_meta() does
> >
> > Signed-off-by: Akinobu Mita <[email protected]>
> > Cc: Andrew Morton <[email protected]>
> > Cc: Stephen Tweedie <[email protected]>
> > Cc: [email protected]
> > Cc: Mingming Cao <[email protected]>
> > Cc: Theodore Tso <[email protected]>
>
> Acked-by: Andreas Dilger <[email protected]>
>
FYI, I have added this patch to patch queue
Mingming
> > ---
> > fs/ext4/balloc.c | 5 ++---
> > 1 file changed, 2 insertions(+), 3 deletions(-)
> >
> > Index: 2.6-git/fs/ext4/balloc.c
> > ===================================================================
> > --- 2.6-git.orig/fs/ext4/balloc.c
> > +++ 2.6-git/fs/ext4/balloc.c
> > @@ -121,9 +121,8 @@ unsigned ext4_init_block_bitmap(struct s
> > le16_to_cpu(sbi->s_es->s_reserved_gdt_blocks);
> > }
> > } else { /* For META_BG_BLOCK_GROUPS */
> > - int group_rel = (block_group -
> > - le32_to_cpu(sbi->s_es->s_first_meta_bg)) %
> > - EXT4_DESC_PER_BLOCK(sb);
> > + int group_rel = block_group % EXT4_DESC_PER_BLOCK(sb);
> > +
> > if (group_rel == 0 || group_rel == 1 ||
> > (group_rel == EXT4_DESC_PER_BLOCK(sb) - 1))
> > bit_max += 1;
>
> Cheers, Andreas
> --
> Andreas Dilger
> Sr. Staff Engineer, Lustre Group
> Sun Microsystems of Canada, Inc.
>