Adding new option to ktrace

[Robert Watson]

On Tue, 6 Sep 2005, Nikhil Dharashivkar wrote:

> Yes, it is ok if i loose data in ktrace queue when crash occurs. 
> Basically, I want to give an Disk IO trace support to ktrace on FreeBSD.
>       So, what I am thinking to use struct dio in dastrategy routine to 
> trace the IO. I 'll use this struct to generate ktr_request. Throught 
> ktr_writerequest it will be written in ktrace.out .
>      Is it possible ?

Try taking a look at KTR(9) and ktrdump(8) for information on ktr, the 
in-kernel trace facility.  ktrace(1) is almost entirely about tracing 
process level system call behavior, and not structured for kernel event 
tracing except in that context.  I think you'll find KTR(9) is much more 
what you're looking for, and among other things, you can extract the 
results from both live kernels and kernel crash dumps.

Robert N M Watson


>
>
>
> On 9/6/05, Peter Jeremy <PeterJeremy at optushome.com.au> wrote:
>> On Tue, 2005-Sep-06 10:33:53 +0530, Nikhil Dharashivkar wrote:
>>>     Thanks for replying me. Basically what happend, while testing
>>> scsi driver on freebsd, at  some point it crashes. So, there is no way
>>> to know how much IO is performed. To know the IO state just before the
>>> driver fails, i selected ktrace to print IO information whatever i ll
>>> get from dastrategy routine.
>>
>> It's not clear how ktrace is going to help here.  The ktrXXX(9)
>> functions place ktr_request events in a queue.  A kernel thread then
>> dumps the queue entries into a file via the normal buffer cache.  The
>> data on disk is typically about 30 seconds behind real time.  If the
>> system crashes, you will lose any events that are still in the buffer
>> cache or ktr_todo queue.
>>
>> Another problem is that since ktrace generates disk I/O, it is likely
>> to disturb your testing.
>>
>> A better approach would seem to be to build a circular buffer and
>> store the I/O requests in the buffer.  When the system crashes, you
>> can look at the last entries in the buffer.
>>
>> --
>> Peter Jeremy
>>
>
>
> -- 
> Thanks and Regards,
>         Nikhil.
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