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    SubjectRe: [PATCH 2/7] proc: Implement support for automounts in task directories
    Andrew Morton <> writes:

    > On Thu, 06 Nov 2008 19:51:23 -0800 (Eric W. Biederman)
    > wrote:
    >> If we could do all of this with reference counting so that the
    >> mount would persist exactly until the last user of it has gone
    >> away without a periodic poll I would love it. But the infrastructure
    >> doesn't support that today,
    > Well that sucks. The free-on-last-put idiom occurs in so many places
    > and serves us so well. I wonder what went wrong here?

    > I guess it has interactions with dentry and inode cache aging which
    > could get tricky.

    At least in part. If you just have the dentry you can't easily
    find what is mounted on it.

    >> and where this is at least partially
    >> a bug fix I would rather not have the change depend on enhancing
    >> the VFS.
    >> The algorithm is actually very aggressive and in practice you don't
    >> see any /proc/<pid>/net showing up as a mount point.
    > Do you think it has failure modes? Most particularly: obscure usage
    > patterns which can cause memory exhaustion?

    I don't think we can pin anything that way that we can't
    pin right now.

    You might be able to pin more if you happen to mount something
    on top of /proc/<pid>/net/ but that is an unprivileged operation.

    >> > Obviously, that becomes clearer as one spends more time with the code,
    >> > but I wonder whether this has all been made as maintainble as it
    >> > possibly could be.
    >> Good question.
    >> In the sense of will we have to go through and futz with the code all
    >> of the time. The abstraction seems good. You put a mount on
    >> the proc_automounts list with do_add_mounts and it goes away eventually
    >> with all of the vfs rules maintained.
    >> In the sense of can the code be read? Perhaps it could be better.
    >> I expect it helps to have run the code and see /proc/net as a filesystem.
    >> that is magically mounted.
    > 'twould be a useful contribution if you were to enshrine your
    > discoveries in /*these things*/. You knew I was working up to that :)

    Short of a big fat comment I'm not certain if there is something I can do


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