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    SubjectQuota mods needed for journaled quota
    Hi,

    There are a few problems in the Linux quota code which make it
    impossible to perform quota updates transactionally when using a
    journaled filesystem.

    Basically we have the following problems:

    * The underlying filesystem does not know which files are the quota
    files, so cannot tell when to apply journaling consistency
    guarantees to data writes

    * "chown" is not transactional: the filesystem is given no
    opportunity to wrap the quota transfer and the owner-attribute
    notify-change call into a single transaction.

    All of these could be fixed very easily (at least for ext3) if it were
    possible for ext3 to install its own version of the superblock->dq_ops
    quota operations (which would just be simple wrappers around the
    existing quota calls). However, the current sys_quotactl installs the
    default quota_ops into the superblock on quota_on without any chance
    for the filesystem to override it.

    The addition of an "init_quota" method to the super_operations struct,
    with quota_on calling this and defaulting to installing the default
    quota_ops if the method is NULL, ought to be sufficient to let ext3
    get quotas right in all cases as far as I can see.

    Comments?

    --Stephen
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