On Tue, Mar 2, 2010 at 3:20 AM, Henrik Johansen <fi...@hotmail.com> wrote:
> Hi folks,
>
> While playing around with the FBT provider I came across something I simply
> can't figure out how to do.
>
> I would really like to track I/O to some of our zvols - for writes something
> like this does the trick :
>
> dtrace -qn 'fbt:zfs:zvol_log_write:entry { @[args[0]->zv_name] = count(); }';
>
> For reads this proves more difficult since the zvol_state struct (which holds
> the zvol name) is not passed as an argument.
>
> I haven't used C since school (more than a decade ago) so excuse me for
> mistaking but
> judging from the zvol_read function in
> http://src.opensolaris.org/source/xref/onnv/onnv-gate/usr/src/uts/common/fs/zfs/zvol.c
> uses a pointer to the zvol_state struct instead.
>
> How can I get my hands on that data from dtrace ?
zvol_read() gets the pointer to the zvol_state struct by caling
ddi_get_soft_state(). You can get this pointer by tracing
ddi_get_soft_state() predicated on being called from inside
zvol_read().
For example, you could do something like this:
fbt::zvol:read:entry
{
self->trace = 1;
}
fbt::ddi_get_soft_state:return
/ self->trace /
{
self->zv = args[1];
}
fbt::zvol_read:return
/ self->zv /
{
@[self->zv->zv_name] = count();
self->zv = 0;
self->trace = 0;
}
Chad
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