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Date: Fri, 8 Apr 2011 11:00:07 -0700
From: Amir Goldstein <amir73il@...il.com>
To: Theodore Tso <tytso@....edu>
Cc: Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: [RFC] exclude bitmap and 32bit bitmap cheksum fields
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
#define EXT2_FEATURE_INCOMPAT_COMPRESSION 0x0001
#define EXT2_FEATURE_INCOMPAT_FILETYPE 0x0002
--
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