Re: [PATCH] blktrace: move trace/ dir to /sys/block/sda/

[Li Zefan <lizf@cn.fujitsu.com>]

Jens Axboe 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.
> 

Ok, I found that patch in btrace mailing list. I'll rebase it and
send it out.

How about just add trace/ to /sys/block/sda? Then if we want to trace
the whole sda, we can:
  # echo 1 > /sys/block/sda/enable
If we want to trace a single partition:
  # echo 1 > /sys/block/sda/sda1/enable

Like "btrace /dev/sda" and "btrace /dev/sda1" when using userspace blktrace.

And when this is done, tracing device-mapper is supported, and I think
current md devices can't be traced by ftrace-plugin blktrace too.

--
Zefan