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    SubjectRe: [PATCH] blktrace: move trace/ dir to /sys/block/sda/
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    On Mon, 2009-04-13 at 22:11 +0200, Ingo Molnar wrote:
    > * Jens Axboe <jens.axboe@oracle.com> wrote:
    >
    > > On Mon, Apr 13 2009, Li Zefan wrote:
    > > > Impact: allow ftrace-plugin blktrace to trace device-mapper devices
    > > >
    > > > blktrace can't trace a single partition, so it makes no sense to
    > > > have one trace/ dir in each /sys/block/sda/sdaX. Move it to
    > > > /sys/block/sda/.
    > > >
    > > > Thus we fix an issue reported by Ted, that ftrace-plugin
    > > > blktrace can't be used to trace device-mapper devices.
    > >
    > > Perhaps I never committed that patch, but it would be trivial to
    > > do partition based blktrace tracing. It's also quite useful. So
    > > please don't go changing things to make that harder to support, it
    > > would be nicer to just add the (small) bits to support
    > > per-partition tracing. It's basically just a start/stop sector
    > > range, while some events are per-device and should just be
    > > included always.
    >
    > btw., per tracepoint filters could be used for that. That would
    > allow multiple partitions to be traced at once.
    >
    > blktrace user-space could make use of sector range filters straight
    > away [ hm, Tom - do we have the <= comparison operator already, or
    > is that still WIP? ] - but i think it's better to do this in a more

    The new comparison operators aren't there yet, but will be part of the
    new parser, which I'll be getting back to this week.

    Tom

    > integrated way: via the sysfs API, via /sys/block/sda/sda2/trace/.
    >
    > So when a partition's trace entry is activated, it would
    > auto-install a specific filter expression for sda, with the sector
    > range of that partition. Or something like that. How does this
    > sound?
    >
    > Ingo



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