Hi Amir,
On 04/09/2011 02:00 AM, Amir Goldstein wrote:
> Hi Ted,
>
> Following our conversation, here is a proposal how to squeeze:
> - 32bit exclude bitmap block address
> - 32bit block+exclude bitmap checksum
> - 32bit inode bitmap checksum
> into the reaming 8 bytes in the group descriptor.
>
> The idea is that the 16bit persistent free inode/block counters
> are redundant to the inode/block bitmap information
> and are needed in 2 use cases:
> 1. sanity checks on fsck
> 2. quick load of in-memory counters
>
> The first use case is nulled by the introduction of inode/block bitmap
> checksums.
> The second use case can be bypassed with no substantial penalty:
> in-memory counters can be calculated on first inode/block bitmap access,
> when the GRP_NEED_INIT (or another) flag is set in the group_info struct,
> just like their cousins, the buddy bitmap counters.
>
> Amir.
>
> diff --git a/lib/ext2fs/ext2_fs.h b/lib/ext2fs/ext2_fs.h
> index 0deb554..5cbaeb2 100644
> --- a/lib/ext2fs/ext2_fs.h
> +++ b/lib/ext2fs/ext2_fs.h
> @@ -153,11 +153,11 @@ struct ext2_group_desc
> __u32 bg_block_bitmap; /* Blocks bitmap block */
> __u32 bg_inode_bitmap; /* Inodes bitmap block */
> __u32 bg_inode_table; /* Inodes table block */
> - __u16 bg_free_blocks_count; /* Free blocks count */
> - __u16 bg_free_inodes_count; /* Free inodes count */
> + __u32 bg_exclude_bitmap; /* Exclude bitmap block */
> __u16 bg_used_dirs_count; /* Directories count */
> __u16 bg_flags;
> - __u32 bg_reserved[2];
> + __u32 bg_block_bitmap_csum; /* Blocks+exclude bitmap checksum */
> + __u32 bg_inode_bitmap_csum; /* Inodes bitmap checksum */
> __u16 bg_itable_unused; /* Unused inodes count */
> __u16 bg_checksum; /* crc16(s_uuid+grouo_num+group_desc)*/
> };
> @@ -170,18 +170,17 @@ struct ext4_group_desc
> __u32 bg_block_bitmap; /* Blocks bitmap block */
> __u32 bg_inode_bitmap; /* Inodes bitmap block */
> __u32 bg_inode_table; /* Inodes table block */
> - __u16 bg_free_blocks_count; /* Free blocks count */
> - __u16 bg_free_inodes_count; /* Free inodes count */
> + __u32 bg_exclude_bitmap; /* Exclude bitmap block */
> __u16 bg_used_dirs_count; /* Directories count */
> __u16 bg_flags;
> - __u32 bg_reserved[2];
> + __u32 bg_block_bitmap_csum; /* Blocks+exclude bitmap checksum */
> + __u32 bg_inode_bitmap_csum; /* Inodes bitmap checksum */
> __u16 bg_itable_unused; /* Unused inodes count */
> __u16 bg_checksum; /* crc16(s_uuid+grouo_num+group_desc)*/
> __u32 bg_block_bitmap_hi; /* Blocks bitmap block MSB */
> __u32 bg_inode_bitmap_hi; /* Inodes bitmap block MSB */
> __u32 bg_inode_table_hi; /* Inodes table block MSB */
> - __u16 bg_free_blocks_count_hi;/* Free blocks count MSB */
> - __u16 bg_free_inodes_count_hi;/* Free inodes count MSB */
> + __u32 bg_exclude_bitmap; /* Exclude bitmap block MSB */
> __u16 bg_used_dirs_count_hi; /* Directories count MSB */
> __u16 bg_pad;
> __u32 bg_reserved2[3];
> @@ -190,6 +189,7 @@ struct ext4_group_desc
> #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
> @@ -751,6 +751,7 @@ struct ext2_super_block {
> #define EXT4_FEATURE_RO_COMPAT_DIR_NLINK 0x0020
> #define EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE 0x0040
> #define EXT4_FEATURE_RO_COMPAT_HAS_SNAPSHOT 0x0080
> +#define EXT4_FEATURE_RO_COMPAT_BITMAP_CSUM 0x0100
I guess this should be in FEATURE_INCOMPAT, not RO_COMPAT?
Since you have changed free_{inodes, blocks}_count to exclude_map. an
old kernel will interpret these values wrongly.
Regards,
Tao
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