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    SubjectRe: [take 3] Use pid in inotify events.
    On Wed, Nov 19, 2008 at 6:53 AM, Evgeniy Polyakov <zbr@ioremap.net> wrote:
    > Hi Michael.
    >
    > On Wed, Nov 19, 2008 at 09:34:46AM -0500, Michael Kerrisk (mtk.manpages@googlemail.com) wrote:
    >> > So effectively you propose to have second generation of the inotify
    >> > which will have additional pid field, which will be unused by all but
    >> > the same uid events?
    >>
    >> I susepect that Christoph wants the same thing as I do: some thinking
    >> towards a future-proof design, rather than a quick hack to address the needs
    >> of a single application.
    >
    > So far the only real need is a pid. That will solve the cases I'm
    > working on and it may be interesting for other applications. It is
    > possible to extend read/write IO with offset and size parameters though.
    >
    > Do you see any other possible extensions?
    >
    >> > If you want to return -EPERM, than it will be _always_ returned for non
    >> > sysadmin capable user, which effectively makes it unusable.
    >> >
    >> Again, appropriate flags in inotify_init1() could fix this -- e.g., only
    >> fill the field (and give an error if no perms) if a flag is set.
    >
    > Um, hmm... Permission is _always_ denied for 'alien' IO, as it was
    > pointed by Robert, at init time there is no way to know, will there be
    > alien IO (i.e. originated by the process with different uid) or not.
    > More on this: inotify initialization is just a memory allocation in
    > the kernel, nothing more.
    >
    > We can argue about object insertion into inotify queue though. But
    > again, we check already that it has read permissions, and if so, we are
    > allowed to receive notificatons about IO against given target, since if
    > new code will return for whatever reason -EPERM, people will use old
    > code.
    >
    > So, putting PID/whatever else into event can be flag-driven, but there
    > is no way to return EPERM anywhere in the call chain not breaking
    > backward compatibility of the whole idea.


    I really don't like the idea of overloading the cookie field to store
    the pid for only the events that don't already use the cookie field.

    Coming into this late, maybe I missed it but can you explain why you
    need the pid that caused the event?

    --
    John McCutchan <john@johnmccutchan.com>


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