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    SubjectRe: [PATCH 3/4] autofs4 - track uid and gid of last mount requestor
    On Thu, 28 Feb 2008 16:08:20 +0900 Ian Kent <> wrote:

    > >
    > > What problem are you actually trying to solve here?
    > The basic problem arises only when we want to restart the user space
    > daemon and there are active autofs managed mounts in place at exit (ie.
    > autofs mounts that have busy user mounts). They are left mounted and
    > processes using them continue to function. But then, when we startup
    > autofs we need to reconnect to these autofs mounts, some of which can
    > covered the by mounted file systems, and hence the need for another way
    > to open an ioctl descriptor to them.

    So we want to store persistant state in the kernel across userspace process
    invokations. That's normally done with a thing called a "file" ;) Could we
    stick all the necessary state into files in a pseudo-fs and have the daemon
    go and open and read them all when it restarts?

    > It may have been overkill to re-implement all the current ioctls (and
    > add a couple of other much needed ones)

    I don't understand that bit. But then, I don't have a clue how autofs

    > but I though it sensible for
    > completeness, and we get to identify any possible problems the current
    > ioctls might have had due to the use of the BKL (by the VFS when calling
    > the ioctls).

    It isn't a good idea to wait for races to reveal themselves. It will take
    years, especially with a system which has as low a call frequency as autofs
    mounting. And once a bug _does_ reveal itself, by then we'll have tens of
    millions of machines out there running that bug.

    > So, why do we need the uid and gid? When someone walks over an autofs
    > dentry that is meant to cause a mount we send a request packet to the
    > daemon via a pipe

    connector or genetlink would be more fashionable transports.

    > which includes the process uid and gid, and as part of
    > the lookup we set macros for several mount map substitution variables,
    > derived from the uid and gid of the process requesting the mount and
    > they can be used within autofs maps.

    yeah, could be a problem. Hopefully the namespace people can advise.
    Perhaps we need a concept of an exportable-to-userspace namespace-id+uid,
    namespace-id+gid, namespace-id+pid, etc for this sort of thing. It has
    come up before. Recently, but I forget what the context was.

    > This is all fine as long as we don't need to re-connect to these mounts
    > when starting up, since we don't get kernel requests for the mounts, we
    > need to obtain that information from the active mount itself.

     \ /
      Last update: 2008-02-28 08:27    [W:0.030 / U:5.468 seconds]
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