Re: REVIEW: handling kldload/kldunload of GEOM classes properly.

From: John Baldwin (jhb_at_FreeBSD.org)
Date: 10/26/04

  • Next message: sonjaya: "xeon" 
    To: freebsd-arch@FreeBSD.org
Date: Tue, 26 Oct 2004 11:53:12 -0400

    On Friday 22 October 2004 05:42 pm, Poul-Henning Kamp wrote:
    > There are a number of system calls which starts events running in
    > GEOM and which for consistency should not return to userland until
    > those events have completed and GEOM has settled down.
    >
    > The typical example would be a shell-script doing:
    >
    > kldload md
    > mdconfig bla bla
    >
    >
    > Examples of such syscalls are:
    >
    > open(2) & close(2): can cause spoils and retastes
    >
    > mount(2)/umount(2): acts as open/close.
    >
    > (any other syscall doing a VOP_OPEN/VOP_CLOSE on a diskdevice.)
    >
    > ioctl(2): directed configuration can do almost anything.
    >
    > kldload(2)/kldunload(2): can load/unload GEOm classes.
    >
    > The last one is the most tricky one: The crude solution is to always
    > wait for geom to settle before returning to userland from kldload(2),
    > but there is no point in waiting for GEOM if you loaded a USB
    > serial driver and doing so would increase the risk of cascade
    > failures.
    >
    > A further complication is that we should not wait for geom to settle
    > until after we have dropped Giant again because the geom events
    > might need to grab giant to do their job.

    Just a note on this: If you sleep in your waiting function (i.e. call
    msleep() or cv_wait()), then Giant will be dropped automatically so that you
    don't need to worry about events needing Giant. 

    -- 
John Baldwin <jhb@FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve!"  -  http://www.FreeBSD.org/
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