Adding new option to ktrace

[Nikhil Dharashivkar]

Hi Scott and Rajesh,
     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.

On 9/6/05, Scott Long <scottl at samsco.org> wrote:
> Rajesh S. Ghanekar wrote:
> > Scott Long wrote:
> >
> >> Nikhil Dharashivkar wrote:
> >>
> >>> Hi,
> >>>    i want to hack the ktrace system call. Basically, I want to monitor
> >>> scsi disk IO through dastrategy() routine.
> >>>     It seems that kern_ktrace.c implements different functions for
> >>> ktrace options like -tc / -ti ... etc (see man page). So, is it
> >>> possible to add new option for disk IO with new structure object
> >>> containing disk io information which will be pass to
> >>> ktr_submittrequest thr' ktr_request structure.
> >>>          Will data will be written correctly in ktrace.out and will
> >>> kdump analyze that ?
> >>>
> >>>
> >>>
> >>
> >> What are you trying to monitor?  Would the existing devstat interface
> >> work?
> >
> >
> > May be he requires how many bytes transferred (read/write) while a
> > process is executing.
> > I guess devstat doesn't do it from process context, it gives total IO
> > read/writes from a device,
> > if registred via devstat. Please correct me if I am wrong.
> >
> >
> > - Rajesh
> >
> 
> There isn't a 1:1 correlation between the bytes that the userland
> program writes, and the bytes that actually get written to disk.
> Filesystem metadata writes will happen if the file needs to be
> extended, not to mention the access time being updated.  Some writes
> won't even originate from a userland program, like swap writes.
> GEOM also decouples the I/O path, so it's not the user process that
> will actually do the write, it's the g_down kthread.  I would think
> that this would make tracking I/O via ktrace very hard.
> 
> Scott
> 


-- 
Thanks and Regards,
         Nikhil.