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    SubjectRe: [PATCHSET] Sysfs cleanups from Eric W. Biederman
    Date
    Tejun Heo <htejun@gmail.com> writes:

    > Hello, all.
    >
    > This is subset of Eric W. Biederman's "Sysfs cleanups & tagged
    > directory support" patchset[1] with the following modifications.

    As a base:
    Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>

    >
    > * fix-i_mutex-locking-in-sysfs_get_dentry patch is added at the top
    > and #14-Don_t-use-lookup_one_len_kern and
    > #15-vfs-Remove-lookup_one_len_kern are dropped. This is because #14
    > contained had a bug where it might created dentry/inode for an
    > already deleted sysfs_dirent. I think it's benefitial to keep
    > single lookup path.

    I think I disagree with the bug spotting.

    At least in net we the sysfs_rename_mutex which keeps parent
    directories from disappearing. Further we have a reference
    to the leaf sysfs_dirent and are actively manipulating it, so
    the sysfs_dirent should not disappear on us.

    > * Rewrote simplify-sysfs_get_dentry patch and
    > #08-Implement-__sysfs_get_dentry,
    > #09-Move-sysfs_get_dentry-below-__sysfs_get_dentry and
    > #10-Rewrite-sysfs_get_dentry-in-terms-of-__sysfs_get_dentry are
    > omitted as __sysfs_get_dentry() isn't used by anyone.

    Right. __sysfs_get_dentry is an optimization that has makes
    the best case for sysfs_get_dentry O(1) instead of O(depth).
    However this doesn't matter because sysfs_get_dentry is not
    on any fast path and the maximum depth of sysfs directories
    is fairly shallow and programmer controlled.

    The only user other user of __sysfs_get_dentry is in the tagged
    directory support, and even that user doesn't strictly need it.
    Although it is a bit silly to populate the dcache just so you
    can invalidate it a moment later...

    Just doing the dget(sysfs_sb->s_root) is a bit clearer in
    sysfs_get_dentry then knowing implicitly that is what
    __sysfs_get_dentry does in the worst cased.

    > * #16, 19-25 are omitted as it isn't clear yet how the tagged entry
    > support will end up.
    >
    > * readdir simplification fixed.
    >
    > * sysfs_mutex double locking fixed.
    >
    > The patchset is on top of the current -gregkh.

    Eric
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