linux-ext4 - Re: [PATCH] libext2fs: reserve exclude bitmap fields in group descriptor

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Date:	Thu, 15 Sep 2011 17:03:37 +0300
From:	Amir Goldstein <amir73il@...il.com>
To:	Andreas Dilger <adilger.kernel@...ger.ca>
Cc:	"Ted Ts'o" <tytso@....edu>, "Darrick J. Wong" <djwong@...ibm.com>,
	Sunil Mushran <sunil.mushran@...cle.com>,
	Andi Kleen <andi@...stfloor.org>,
	Mingming Cao <cmm@...ibm.com>,
	Joel Becker <jlbec@...lplan.org>, linux-ext4@...r.kernel.org,
	Coly Li <colyli@...il.com>,
	Yongqiang Yang <xiaoqiangnk@...il.com>
Subject: Re: [PATCH] libext2fs: reserve exclude bitmap fields in group descriptor

On Thu, Sep 15, 2011 at 1:06 PM, Andreas Dilger
<adilger.kernel@...ger.ca> wrote:
> On 2011-09-15, at 12:50 AM, Amir Goldstein wrote:
>> Here is a patch to reserve the exclude bitmap field, so we won't
>> forget them again...
>> The full patch series for adding exclude bitmap can be found here:
>> https://github.com/amir73il/e2fsprogs-snapshots-patch-queue
>>
>> ---
>> From: Amir Goldstein <amir73il@...rs.sf.net>
>> Date: Thu, 15 Sep 2011 09:42:38 +0300
>>
>> Ext4 snapshots require the compatible feature 'exclude_bitmap', meaning that
>> the exclude bitmap was allocated.
>> The allocated exclude bitmap blocks are stored in the block group descriptors.
>>
>> To allow easy migration of existing Next3 installations, I took the liberty
>> of 'burning' the old 'exclude_inode' compatible flag and using a new
>> 'exclude_bitmap' comaptible flag, to state the exclude bitmap blocks are stored
>> in the group descriptors.
>>
>> Signed-off-by: Amir Goldstein <amir73il@...rs.sf.net>
>> ---
>> lib/ext2fs/ext2_fs.h |   13 +++++++++----
>> 1 files changed, 9 insertions(+), 4 deletions(-)
>>
>> diff --git a/lib/ext2fs/ext2_fs.h b/lib/ext2fs/ext2_fs.h
>> index 54cb3d4..f1f0e19 100644
>> --- a/lib/ext2fs/ext2_fs.h
>> +++ b/lib/ext2fs/ext2_fs.h
>> @@ -142,7 +142,8 @@ struct ext2_group_desc
>>        __u16   bg_free_inodes_count;   /* Free inodes count */
>>        __u16   bg_used_dirs_count;     /* Directories count */
>>        __u16   bg_flags;
>> -       __u32   bg_reserved[2];
>> +       __u32   bg_exclude_bitmap;      /* Exclude bitmap block */
>
> I'd prefer if these comments were "Snapshot exclude bitmap block" so
> that it is more clear what an exclude bitmap is used for.

I'll change that.

>
> For consistency, it would also be good to name these "_lo" to match the
> kernel fields.
>

That's a major cleanup.
Forgive me for not picking up that glove...

>> +       __u32   bg_reserved[1];
>>        __u16   bg_itable_unused;       /* Unused inodes count */
>>        __u16   bg_checksum;            /* crc16(s_uuid+grouo_num+group_desc)*/
>> };
>> @@ -159,7 +160,8 @@ struct ext4_group_desc
>>        __u16   bg_free_inodes_count;   /* Free inodes count */
>>        __u16   bg_used_dirs_count;     /* Directories count */
>>        __u16   bg_flags;               /* EXT4_BG_flags (INODE_UNINIT, etc) */
>> -       __u32   bg_reserved[2];         /* Likely block/inode bitmap checksum */
>> +       __u32   bg_exclude_bitmap;      /* Exclude bitmap block */
>> +       __u32   bg_reserved[1];         /* Likely block/inode bitmap checksum */
>>        __u16   bg_itable_unused;       /* Unused inodes count */
>>        __u16   bg_checksum;            /* crc16(sb_uuid+group+desc) */
>>        __u32   bg_block_bitmap_hi;     /* Blocks bitmap block MSB */
>>
>> @@ -169,12 +171,14 @@ struct ext4_group_desc
>>        __u16   bg_free_inodes_count_hi;/* Free inodes count MSB */
>>        __u16   bg_used_dirs_count_hi;  /* Directories count MSB */
>>        __u16   bg_itable_unused_hi;    /* Unused inodes count MSB */
>> -       __u32   bg_reserved2[3];
>> +       __u32   bg_exclude_bitmap_hi;   /* Exclude bitmap block MSB */
>> +       __u32   bg_reserved2[2];
>> };
>>
>> #define EXT2_BG_INODE_UNINIT   0x0001 /* Inode table/bitmap not initialized */
>> #define EXT2_BG_BLOCK_UNINIT   0x0002 /* Block bitmap not initialized */
>> #define EXT2_BG_INODE_ZEROED   0x0004 /* On-disk itable initialized to zero */
>> +#define EXT2_BG_EXCLUDE_UNINIT 0x0008 /* Exclude bitmap not initialized */
>>
>> /*
>>  * Data structures used by the directory indexing feature
>> @@ -670,7 +674,8 @@ struct ext2_super_block {
>> #define EXT2_FEATURE_COMPAT_RESIZE_INODE       0x0010
>> #define EXT2_FEATURE_COMPAT_DIR_INDEX          0x0020
>> #define EXT2_FEATURE_COMPAT_LAZY_BG            0x0040
>> -#define EXT2_FEATURE_COMPAT_EXCLUDE_INODE      0x0080
>> +/* #define EXT2_FEATURE_COMPAT_EXCLUDE_INODE   0x0080 not used */
>> +#define EXT2_FEATURE_COMPAT_EXCLUDE_BITMAP     0x0100
>>
>> #define EXT2_FEATURE_RO_COMPAT_SPARSE_SUPER    0x0001
>> #define EXT2_FEATURE_RO_COMPAT_LARGE_FILE      0x0002
>> --
>> 1.7.0.4
>
>
> Cheers, Andreas
>
>
>
>
>
>
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