Hm, well, the problem is (I believe) that with the "-o" option just
isn't designed to work with multiple devices.
Brett: The simplest thing to do for your example would be:
# blktrace /dev/sdbk /dev/sdam
...
# blkparse -q sdbk sdam
Basically, listing each device used on the blkparse line. [That's how I
(and presumably everyone else) has always done it.]
The technical reason why "-o" doesn't work with multiple devices is
because we use multiple threads of execution - one per device/CPU pair -
and each of them opens a file named "<prefix>.blktrace.<cpu>". With the
"-o" all of the "<prefix>" values are the same - so multiple threads
open the same file and try to do output. Not good. Without the "-o" we
get unique files named: "<device>.blktrace.<cpu>" - as the tuple
(<device>,<cpu>) is unique.
I suppose we could change the definition of "-o" to be:
"<prefix>.<device>.blktrace.<cpu>" - but I don't know what else this
would break. So, I think what I'll do is update the documentation to
just note that "-o" doesn't work with multiple devices.
Regards,
Alan
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