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 the 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 %15s\n", "DEVICE", "APP", "PID", "BYTES");
                   printa("%10s %20s %10d %15@d\n", @);
           }

COMPATIBILITY

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

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>.

BUGS

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