From: Amir Goldstein Subject: [RFC] exclude bitmap and 32bit bitmap cheksum fields Date: Fri, 8 Apr 2011 11:00:07 -0700 Message-ID: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Cc: Ext4 Developers List To: Theodore Tso Return-path: Received: from mail-qw0-f46.google.com ([209.85.216.46]:41747 "EHLO mail-qw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757348Ab1DHSAI (ORCPT ); Fri, 8 Apr 2011 14:00:08 -0400 Received: by qwk3 with SMTP id 3so2241950qwk.19 for ; Fri, 08 Apr 2011 11:00:07 -0700 (PDT) Sender: linux-ext4-owner@vger.kernel.org List-ID: 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