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    SubjectRe: [PATCH 0/2] add new notifier function ,take3
    On Mon, 14 Apr 2008 12:01:46 -0400
    Neil Horman <nhorman@redhat.com> wrote:

    > On Mon, Apr 14, 2008 at 10:53:23AM -0400, Vivek Goyal wrote:
    > > On Mon, Apr 14, 2008 at 10:42:28AM -0400, Neil Horman wrote:
    > > > On Mon, Apr 14, 2008 at 09:46:22AM -0400, Vivek Goyal wrote:
    > > > > On Fri, Apr 11, 2008 at 09:07:51PM -0700, Andrew Morton wrote:
    > > > >
    > > > > [..]
    > > > > > > Kernel panic - not syncing: Panic by panic_module.
    > > > > > > __tunable_atomic_notifier_call_chain enter
    > > > > > > msg_handler:panic_event was called.
    > > > > > > ipmi_wdog:wdog_panic_handler was called.
    > > > > > > notifier_test: notifier_test_panic() is called.
    > > > > > > notifier_test: notifier_test_panic2() is called.
    > > > > >
    > > > > > OK. But I don't see anywhere in here the most important piece of
    > > > > > information: why do we need this feature in Linux?
    > > > > >
    > > > > > What are the use-cases? What is the value? etc.
    > > > > >
    > > > > > Often I can guess (but I like the originator to remove the guesswork). In
    > > > > > this case I'm stumped - I can't see any reason why anyone would want this.
    > > > > >
    > > > >
    > > > > Hi Andrew,
    > > > >
    > > > > To begin with, he wants kdb, kgdb etc to co-exist with kdump. He wants
    > > > > to put all the RAS tools (who are interested in panic event) on a list
    > > > > and export it to user space and let user decide in what order do the tool get
    > > > > executed at panic time (based on priority).
    > > > >
    > > > > This brings in little bit reliability concerns for kdump due to notifier
    > > > > code being run after panic.
    > > > >
    > > > > I think people want to use this infrastrutucure beyond RAS tools. I
    > > > > remember somebody wanting to send a message to remote node after a
    > > > > panic (before kdump kicks in) so that remote node can initiate failover
    > > > > etc.
    > > > >
    > > > I know it doesn't particularly relate to this patch, but FWIW, for cases like
    > > > failover, I've inserted infrastrucutre in the userspace part of kdump for
    > > > Fedora/RHEL to support this sort of thing. We can run arbitrary scripts righte
    > > > before and after a capture so that notifications can be sent to remote nodes in
    > > > a much safer fashion than using the notifier chain after a panic.
    > > > Neil
    > > >
    > >
    > > That's great. I did not know about these. So user can write custom
    > > scripts/binaries which can be packed into kdump initrd and executed either
    > > before or after dump capture? Any idea, if somebody has started using it
    > > already?
    > >
    > Thats exactly right. I'm not sure if there is any serious use as of yet, but
    > I've had some interrogatories about it. Specific cases that I recall include:
    >
    > 1) A set of users in japan that are using the pre-dump script to block execution
    > until a scsi controller detects all its drives (it apparently takes up to three
    > minues to scan its bus)
    >
    > 2) I think some people using clustering services were using the pre-script to
    > notify cluster peers of the failure to avoid power fencing while a node
    > completed the crash dump
    >
    > 3) A national lab had an interest in using the pre script to send an email to an
    > administrative address to log the failure in a cluster
    >

    OK, thanks.

    I think I'll duck the patch for now as it seems that a littlee more thought
    and coordination is neeed.

    Plus it appears that the only users of this infrastructure are provided via
    presently-out-of-tree patches, so people who are already patching and
    building their own kernels can easily add this other patch as well, for now.


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