From: Tao Ma Subject: Re: [RFC] exclude bitmap and 32bit bitmap cheksum fields Date: Sat, 09 Apr 2011 02:45:24 +0800 Message-ID: <4D9F57C4.4010306@tao.ma> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Theodore Tso , Ext4 Developers List To: Amir Goldstein Return-path: Received: from cpoproxy2-pub.bluehost.com ([67.222.39.38]:51867 "HELO cpoproxy2-pub.bluehost.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1756293Ab1DHSp3 (ORCPT ); Fri, 8 Apr 2011 14:45:29 -0400 In-Reply-To: Sender: linux-ext4-owner@vger.kernel.org List-ID: 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