• Tao Ma's avatar
    ocfs2: Enable xattr set in index btree · 01225596
    Tao Ma authored
    Where the previous patches added the ability of list/get xattr in buckets
    for ocfs2, this patch enables ocfs2 to store large numbers of EAs.
    The original design doc is written by Mark Fasheh, and it can be found in
    http://oss.oracle.com/osswiki/OCFS2/DesignDocs/IndexedEATrees. I only had to
    make small modifications to it.
    First, because the bucket size is 4K, a new field named xh_free_start is added
    in ocfs2_xattr_header to indicate the next valid name/value offset in a bucket.
    It is used when we store new EA name/value. With this field, we can find the
    place more quickly and what's more, we don't need to sort the name/value every
    time to let the last entry indicate the next unused space. This makes the
    insert operation more efficient for blocksizes smaller than 4k.
    Because of the new xh_free_start, another field named as xh_name_value_len is
    also added in ocfs2_xattr_header. It records the total length of all the
    name/values in the bucket. We need this so that we can check it and defragment
    the bucket if there is not enough contiguous free space.
    An xattr insertion looks like this:
    1. xattr_index_block_find: find the right bucket by the name_hash, say bucketA.
    2. check whether there is enough space in bucketA. If yes, insert it directly
       and modify xh_free_start and xh_name_value_len accordingly. If not, check
       xh_name_value_len to see whether we can store this by defragment the bucket.
       If yes, defragment it and go on insertion.
    3. If defragement doesn't work, check whether there is new empty bucket in
       the clusters within this extent record. If yes, init the new bucket and move
       all the buckets after bucketA one by one to the next bucket. Move half of the
       entries in bucketA to the next bucket and go on insertion.
    4. If there is no new bucket, grow the extent tree.
    As for xattr deletion, we will delete an xattr bucket when all it's xattrs
    are removed and move all the buckets after it to the previous one. When all
    the xattr buckets in an extend record are freed, free this extend records
    from ocfs2_xattr_tree.
    Signed-off-by: default avatarTao Ma <tao.ma@oracle.com>
    Signed-off-by: default avatarMark Fasheh <mfasheh@suse.com>
xattr.h 2.15 KB