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    SubjectRe: [RFC PATCH] Introduce filesystem type tracking
    2008/5/20 Al Viro <>:
    > On Tue, May 20, 2008 at 02:06:42PM +0100, Tom Spink wrote:
    > [snip]
    >> I'm just adding people to CC here, but also I had a couple of thoughts
    >> after reviewing my own code.
    >> I see that do_kern_mount is encapsulated with the BKL, but would it be
    >> wise to introduce a lock (e.g. a mutex) now for reading and updating
    >> nr_mounts (and hence calling ->init), rather than wait for the BKL
    >> removal to come round here?
    >> Also, have I got all the cases where a filesystem is unmounted,
    >> because I now see umount_tree, and am wondering if decrementing the
    >> nr_mounts field should be done in here, in the loop of vfsmounts... or
    >> is it sufficient to leave it at the end of do_umount?

    Hi Al,

    > No, you have not and no, doing that anywhere near that layer is hopeless.
    > a) Instances of filesystem can easily outlive all vfsmounts,
    > let alone their attachment to namespaces.

    I see! Whoops...

    > b) What should happen if init is done in the middle of exit?

    Okay, I guess *some* sort of locking is in order. :)

    > c) Why do we need to bother, anyway?

    Well, just for the reason I mentioned, I saw the posting about XFS
    starting threads (when compiled into the kernel), but there's no use
    of an XFS filesystem at all - there was a suggestion that something
    like this be tried, so I thought I'd give it a go.

    Thanks for replying!

    Tom Spink

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