.\" Copyright (c) 2015 Mark Johnston <markj@FreeBSD.org>
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.Dd April 18, 2015
.Dt DTRACE_IO 4
.Os
.Sh NAME
.Nm dtrace_io
.Nd a DTrace provider for tracing events related to disk I/O
.Sh SYNOPSIS
.Fn io:::start "struct bio *" "struct devstat *"
.Fn io:::done "struct bio *" "struct devstat *"
.Sh DESCRIPTION
The
.Nm io
provider allows the tracing of disk I/O events.
The
.Fn io:::start
probe fires when a I/O request is about to be sent to the backing driver of a
.Xr disk 9
object.
This occurs after all
.Xr GEOM 4
transformations have been performed on the request.
The
.Fn io:::done
probe fires when a I/O request is completed.
Both probes take a
.Vt "struct bio *"
representing the I/O request as their first argument.
The second argument is a
.Vt "struct devstat *"
for the underlying
.Xr disk 9
object.
.Sh ARGUMENTS
The fields of
.Vt "struct bio"
are described in the
.Xr g_bio 9
manual page, and the fields of
.Vt "struct devstat"
are described in the
.Xr devstat 9
manual page.
Translators for the
.Vt bufinfo_t
and
.Vt devinfo_t
D types are defined in
.Pa /usr/lib/dtrace/io.d .
.Sh FILES
.Bl -tag -width "/usr/lib/dtrace/io.d" -compact
.It Pa /usr/lib/dtrace/io.d
DTrace type and translator definitions for the
.Nm io
provider.
.El
.Sh EXAMPLES
The following script shows a per-process breakdown of total I/O by disk device:
.Bd -literal -offset indent
#pragma D option quiet

io:::start
{
        @[args[1]->device_name, execname, pid] = sum(args[0]->bio_bcount);
}

END
{
        printf("%10s %20s %10s %15s\\n", "DEVICE", "APP", "PID", "BYTES");
        printa("%10s %20s %10d %15@d\\n", @);
}
.Ed
.Sh COMPATIBILITY
This provider is not compatible with the
.Nm io
provider found in Solaris, as its probes use native
.Fx
argument types.
.Sh SEE ALSO
.Xr dtrace 1 ,
.Xr devstat 9 ,
.Xr SDT 9
.Sh HISTORY
The
.Nm io
provider first appeared in
.Fx
9.2 and 10.0.
.Sh AUTHORS
This manual page was written by
.An Mark Johnston Aq Mt markj@FreeBSD.org .
.Sh BUGS
The
.Fn io:::wait-start
and
.Fn io:::wait-done
probes are not currently implemented on
.Fx .