On Sep 28, 2006 10:55 +0200, Alexandre Ratchov wrote:
> here is a list of fields we plan to use for the 64bit support, they must be
> zero on file systems without the EXT4_FEATURE_INCOMPAT_64BIT.
>
> struct ext4_super_block
> {
> /* at offset 0xfe */
> __le32 s_desc_size; /* Group descriptor size */
I believe this is actually a __u16 and not __u32. The group descriptor
can't be larger than a filesystem block anyways. Formerly called
s_reserved_word_pad.
> > - EXT4_FEATURE_RO_COMPAT_GDT_CSUM (0x0010?) - store a crc16 checksum in
> > the group descriptor (s_uuid[16] | __u32 group | ext3_group_desc
> > (excluding gd_checksum itself)). This allows the kernel to more safely
> > manage UNINIT groups. Incomplete patch, e2fsck support mostly done.
struct ext3_group_desc
{
__le32 bg_block_bitmap; /* Blocks bitmap block */
__le32 bg_inode_bitmap; /* Inodes bitmap block */
__le32 bg_inode_table; /* Inodes table block */
__le16 bg_free_blocks_count; /* Free blocks count */
__le16 bg_free_inodes_count; /* Free inodes count */
__le16 bg_used_dirs_count; /* Directories count */
- __u16 bg_pad;
- __le32 bg_reserved[3];
+ __le16 bg_flags;
+ __le32 bg_reserved[2];
+ __le16 bg_itable_unused; /*Unused inodes count*/
+ __le16 bg_checksum; /*crc16(s_uuid+group_num+group_desc)*/
};
> > - EXT4_FEATURE_RO_COMPAT_DIR_NLINK (0x0020?) - allow directories to have >
> > 65000 subdirectories (i_nlinks) by setting i_nlinks = 1 for such
> > directories. RO_COMPAT protects old filesystems from unlinking such
> > directories incorrectly and losing all files therein. Needs RO_COMPAT
> > flag handling, needs e2fsck support, but very heavily tested.
No extra fields needed, just compat. Bumps EXT3_LINK_MAX to 65000.
> > - EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE (0x0040?) - add s_min_extra_isize and
> > s_want_extra_isize fields to superblock, which allow specifying
> > the minimum and desired i_extra_isize fields in large inodes
> > (for nsec+epoch timestamps, potential other uses). Needs RO_COMPAT
> > flag handling, needs e2fsck support, patch complete, little testing.
No patch yet which uses s_*_extra_isize, they can go in next available slots.
struct ext3_inode {
} osd2; /* OS dependent 2 */
__le16 i_extra_isize;
__le16 i_pad1;
__le32 i_ctime_extra; /* extra Change time (nsec << 2 | epoch) */
__le32 i_mtime_extra; /* extra Modification time(nsec << 2 | epoch) */
__le32 i_atime_extra; /* extra Access time (nsec << 2 | epoch) */
__le32 i_extra_reserved1;
}
> There's also the change attribute patch; it currently uses the l_i_reserved2
> field of the inode:
>
> - __u32 l_i_reserved2;
> + __le32 l_i_change_attribute;
>
> -#define i_reserved2 osd2.linux2.l_i_reserved2
> +#define i_chattr osd2.linux2.l_i_change_attribute
>
> It doesn't need RO_COMPAT/INCOMPAT flag because there are no incompatibility
> issues with kernels that do not support the change attribute but that mount
> file systems that have used it. Also it doesn't really need changes in fsck.
Did we decide if l_i_change_attribute would also be the ctime nsec value?
That would affect the RO_COMPAT_EXTRA_ISIZE implementation above, putting
the i_ctime_extra in place of l_i_reserved2. That doesn't change the
patch significantly, though it does need the "always increment" change.
Cheers, Andreas
--
Andreas Dilger
Principal Software Engineer
Cluster File Systems, Inc.
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