DTRACE-IO(4)	       FreeBSD Kernel Interfaces Manual 	  DTRACE-IO(4)

NAME
     dtrace-io – a DTrace provider for tracing events related to disk I/O

SYNOPSIS
     io:::start(struct bio *, struct devstat *);

     io:::done(struct bio *, struct devstat *);

DESCRIPTION
     The io provider allows the tracing of disk I/O events.  The io:::start()
     probe fires when a I/O request is about to be sent to the backing driver
     of a disk(9) object.  This occurs after all GEOM(4) transformations have
     been performed on the request.  The io:::done() probe fires when a I/O
     request is completed.  Both probes take a struct bio * representing the
     I/O request as their first argument.  The second argument is a struct
     devstat * for the underlying disk(9) object.

ARGUMENTS
     The fields of struct bio are described in the g_bio(9) manual page, and
     the fields of struct devstat are described in the devstat(9) manual page.
     Translators for the bufinfo_t and devinfo_t D types are defined in
     /usr/lib/dtrace/io.d.

FILES
     /usr/lib/dtrace/io.d  DTrace type and translator definitions for io
			   provider.

EXAMPLES
     The following script shows a per-process breakdown of total I/O by disk
     device:

	   #pragma D option quiet

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

	   END
	   {
		   printf("%10s %20s %10s %15s0, "DEVICE", "APP", "PID", "BYTES");
		   printa("%10s %20s %10d %15@d0, @);
	   }

COMPATIBILITY
     This provider is not compatible with the io provider found in Solaris, as
     its probes use native FreeBSD argument types.

     The io:::wait-start() and io:::wait-done() probes are not currently
     implemented on FreeBSD.

SEE ALSO
     dtrace(1), devstat(9), SDT(9)

HISTORY
     The io provider first appeared in FreeBSD 9.2 and 10.0.

AUTHORS
     This manual page was written by Mark Johnston <markj@FreeBSD.org>.

FreeBSD 11.0-CURRENT		March 22, 2015		  FreeBSD 11.0-CURRENT