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    SubjectRe: [PATCH 1/3] Add extended attributes to ext2/3
    Date
    On Wednesday 16 October 2002 02:00, Andrew Morton wrote:
    > tytso@mit.edu wrote:
    > > This is an updated submission of the extended attribute patches for
    > > ext2/3 (versus bk-current). Many thanks to Cristoph, Andrea, and Andrew
    > > for their suggestions and cleanups.
    > >
    > > This patch creates a meta block cache which is utilized by the ext3 and
    > > ext2 extended attribute patches (patches 2 and 3, respectively). This
    > > cache allows directory blocks to be indexed by multiple keys. In the
    > > case of the extended attribute patches, it is used to look up blocks by
    > > both the block number and by the hash of the extended attributes. This
    > > is extremely important to allow the sharing of acl's when stored as
    > > extended attributes. Otherwise every single file would require its own,
    > > separate, one block overhead to store then ACL, even though there might
    > > be a large number of files that have the same ACL.
    >
    > The key thing here appears to be the cache entry:
    >
    > +struct mb_cache_entry {
    > + struct list_head e_lru_list;
    > + struct mb_cache *e_cache;
    > + atomic_t e_used;
    > + dev_t e_dev;
    > + unsigned long e_block;
    > + struct list_head e_block_list;
    > + struct mb_cache_entry_index e_indexes[0];
    > +};
    >
    > This should be converted to use sector_t for >2TB support, and tested
    > with CONFIG_LBD=y and n.

    e_block is the block number; the e_indexes are hash values. Ext[23] only has
    32bit block numbers. Am I getting you wrong?

    > The use of a dev_t search key is a bit old-fashioned. Maybe
    > use the address of inode->i_sb->s_bdev?

    That would do as well.

    A related issue:

    Would switching to a more decent hash algorithm in fs/ext?/xattr.c make sense?
    I think there are better ones in 2.5. This would only degrade sharing on
    "legacy" systems for a while, but the slow down would vanish over time.

    --Andreas.

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