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
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