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    SubjectRe: [PATCH][v3] blktrace: conversion to tracepoints
    On Mon, Nov 03 2008, Arnaldo Carvalho de Melo wrote:
    > Em Thu, Oct 30, 2008 at 12:11:45PM +0100, Jens Axboe escreveu:
    > > On Thu, Oct 30 2008, Arnaldo Carvalho de Melo wrote:
    > > > Yes, I tested it, run 'btrace /dev/sda' several times, while doing a
    > > > 45 GB backup using rsync over NFS, etc. So it should have exercised the
    > > > tracepoints use and repeated registrater/unregister cycles.
    > >
    > > Awesome, just wanted to know what level of testing you had done (from
    > > "none" to "doesn't crash" to "actually works"), so thanks for that.
    >
    > Jens,
    >
    > Now I'm working on the marker glue code for systemtap to use
    > these tracepoints and I noticed that one important piece of information
    > is not available unless one first uses blk_trace_ioctl to fill in
    > request_queue->blk_trace, that is request_queue->blk_trace->dev, i.e.
    > the device associated with the request_queue.
    >
    > Is there a way to, from the request_queue, get the dev? I guess
    > not, as if there would be you wouldn't have added it to struct
    > blk_trace...
    >
    > Would it be sane to add get struct block_device->bd_dev dev_t
    > info into struct request_queue at sd_probe time or most probably at some
    > more suitable routine in the device/disk registration sequence of
    > events?

    You can't do that, the queue is nothing more than a transport. There's
    no sane way to map from a queue to a device, since it's not given that
    there will be a 1:1 mapping even. So no go there, sorry.

    > I am certainly missing lots of connections here, there are many
    > objects and relationships among these objects that may make the
    > association of a block_device with a request_queue not to be fixed all
    > the time, thus requiring the struct blk_trace ->dev field to be set up
    > at ioctl time, but I'm just trying to figure out how to remove the
    > requirement of a setup routine for the tracepoints to know what is the
    > dev_t associated with the request_queue they are getting as a parameter.
    >
    > Best Regards,
    >
    > - Arnaldo
    > --
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    --
    Jens Axboe



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