Teach NOP GEOM class how to gather the following statistics:

- number of read I/O requests,
- number of write I/O requests,
- number of read bytes,
- number of written bytes.
Add 'reset' subcommand for resetting statistics.

sbin/geom/class/nop/geom_nop.c

@@ -68,5 +68,8 @@ struct g_command class_commands[] = {
 	    },
 	    "[-fv] prov ..."
 	},
+	{ "reset", G_FLAG_VERBOSE, NULL, G_NULL_OPTS,
+	    "[-v] prov ..."
+	},
 	G_CMD_SENTINEL
 };

sbin/geom/class/nop/gnop.8

@@ -49,6 +49,10 @@
 .Op Fl fv
 .Ar prov ...
 .Nm
+.Cm reset
+.Op Fl v
+.Ar prov ...
+.Nm
 .Cm list
 .Nm
 .Cm status
@@ -62,7 +66,10 @@ The
 utility is used for setting up transparent providers on existing ones.
 Its main purpose is testing other GEOM classes, as it allows forced provider
 removal and I/O error simulation with a given probability.
-It is also a good starting point for implementing new GEOM classes.
+It also gathers the following statistics: number of read requests, number of
+write requests, number of read bytes and number of wrote bytes.
+In addition, it can be used as a good starting point for implementing new GEOM
+class.
 .Pp
 The first argument to
 .Nm
@@ -77,13 +84,11 @@ The kernel module
 will be loaded if it is not loaded already.
 .It Cm configure
 Configure existing transparent provider.
-At the moment it is only used
-for changing failure probability.
-The kernel module
-.Pa geom_nop.ko
-will be loaded if it is not loaded already.
+At the moment it is only used for changing failure probability.
 .It Cm destroy
 Turn off the given transparent providers.
+.It Cm reset
+Reset statistics for the given transparent providers.
 .It Cm list
 See
 .Xr geom 8 .
@@ -139,6 +144,17 @@ with 50% failure probability, and how to destroy it.
 gnop create -v -f 50 da0
 gnop destroy -v da0.nop
 .Ed
+.Pp
+The traffic statistics for the given transparent providers we can get with
+.Cm list
+command.
+Example below shows how can we obtain number of bytes written with
+.Xr newfs 8 :
+.Bd -literal -offset indent
+gnop create da0
+newfs /dev/da0.nop
+gnop list
+.Ed
 .Sh SEE ALSO
 .Xr geom 4 ,
 .Xr geom 8

sys/geom/nop/g_nop.c

@@ -86,6 +86,16 @@ g_nop_start(struct bio *bp)
 		g_io_deliver(bp, ENOMEM);
 		return;
 	}
+	switch (bp->bio_cmd) {
+	case BIO_READ:
+		sc->sc_reads++;
+		sc->sc_readbytes += bp->bio_length;
+		break;
+	case BIO_WRITE:
+		sc->sc_writes++;
+		sc->sc_wrotebytes += bp->bio_length;
+		break;
+	}
 	if (sc->sc_failprob > 0) {
 		u_int rval;
 
@@ -176,6 +186,10 @@ g_nop_create(struct gctl_req *req, struct g_class *mp, struct g_provider *pp,
 	sc = g_malloc(sizeof(*sc), M_WAITOK);
 	sc->sc_offset = offset;
 	sc->sc_failprob = failprob;
+	sc->sc_reads = 0;
+	sc->sc_writes = 0;
+	sc->sc_readbytes = 0;
+	sc->sc_wrotebytes = 0;
 	gp->softc = sc;
 	gp->start = g_nop_start;
 	gp->orphan = g_nop_orphan;
@@ -448,6 +462,50 @@ g_nop_ctl_destroy(struct gctl_req *req, struct g_class *mp)
 	}
 }
 
+static void
+g_nop_ctl_reset(struct gctl_req *req, struct g_class *mp)
+{
+	struct g_nop_softc *sc;
+	struct g_provider *pp;
+	const char *name;
+	char param[16];
+	int i, *nargs;
+
+	g_topology_assert();
+
+	nargs = gctl_get_paraml(req, "nargs", sizeof(*nargs));
+	if (nargs == NULL) {
+		gctl_error(req, "No '%s' argument", "nargs");
+		return;
+	}
+	if (*nargs <= 0) {
+		gctl_error(req, "Missing device(s).");
+		return;
+	}
+
+	for (i = 0; i < *nargs; i++) {
+		snprintf(param, sizeof(param), "arg%d", i);
+		name = gctl_get_asciiparam(req, param); 
+		if (name == NULL) {
+			gctl_error(req, "No 'arg%d' argument", i);
+			return;
+		}
+		if (strncmp(name, "/dev/", strlen("/dev/")) == 0)
+			name += strlen("/dev/");
+		pp = g_provider_by_name(name);
+		if (pp == NULL || pp->geom->class != mp) {
+			G_NOP_DEBUG(1, "Provider %s is invalid.", name);
+			gctl_error(req, "Provider %s is invalid.", name);
+			return; 
+		}
+		sc = pp->geom->softc;
+		sc->sc_reads = 0;
+		sc->sc_writes = 0;
+		sc->sc_readbytes = 0;
+		sc->sc_wrotebytes = 0;
+	}
+}
+
 static void
 g_nop_config(struct gctl_req *req, struct g_class *mp, const char *verb)
 {
@@ -474,6 +532,9 @@ g_nop_config(struct gctl_req *req, struct g_class *mp, const char *verb)
 	} else if (strcmp(verb, "destroy") == 0) {
 		g_nop_ctl_destroy(req, mp);
 		return;
+	} else if (strcmp(verb, "reset") == 0) {
+		g_nop_ctl_reset(req, mp);
+		return;
 	}
 
 	gctl_error(req, "Unknown verb.");
@@ -490,7 +551,13 @@ g_nop_dumpconf(struct sbuf *sb, const char *indent, struct g_geom *gp,
 	sc = gp->softc;
 	sbuf_printf(sb, "%s<Offset>%jd</Offset>\n", indent,
 	    (intmax_t)sc->sc_offset);
-	sbuf_printf(sb, "%s<Failprob>%u</Failprob>\n", indent, sc->sc_failprob);
+	sbuf_printf(sb, "%s<FailProb>%u</FailProb>\n", indent, sc->sc_failprob);
+	sbuf_printf(sb, "%s<Reads>%ju</Reads>\n", indent, sc->sc_reads);
+	sbuf_printf(sb, "%s<Writes>%ju</Writes>\n", indent, sc->sc_writes);
+	sbuf_printf(sb, "%s<ReadBytes>%ju</ReadBytess>\n", indent,
+	    sc->sc_readbytes);
+	sbuf_printf(sb, "%s<WroteBytes>%ju</WroteBytes>\n", indent,
+	    sc->sc_writebytes);
 }
 
 DECLARE_GEOM_CLASS(g_nop_class, g_nop);

sys/geom/nop/g_nop.h

@@ -55,8 +55,12 @@
 } while (0)
 
 struct g_nop_softc {
-	off_t	sc_offset;
-	u_int	sc_failprob;
+	off_t		sc_offset;
+	u_int		sc_failprob;
+	uintmax_t	sc_reads;
+	uintmax_t	sc_writes;
+	uintmax_t	sc_readbytes;
+	uintmax_t	sc_wrotebytes;
 };
 #endif	/* _KERNEL */