freebsd-skq/sys/geom/geom_disk.c
mav 24017b5387 Implement media change notification for DA and CD removable media devices.
It includes three parts:
 1) Modifications to CAM to detect media media changes and report them to
disk(9) layer. For modern SATA (and potentially UAS) devices it utilizes
Asynchronous Notification mechanism to receive events from hardware.
Active polling with TEST UNIT READY commands with 3 seconds period is used
for incapable hardware. After that both CD and DA drivers work the same way,
detecting two conditions: "NOT READY: Medium not present" after medium was
detected previously, and "UNIT ATTENTION: Not ready to ready change, medium
may have changed". First one reported to disk(9) as media removal, second
as media insert/change. To reliably receive second event new
AC_UNIT_ATTENTION async added to make UAs broadcasted to all periphs by
generic error handling code in cam_periph_error().
 2) Modifications to GEOM core to handle media remove and change events.
Media removal handled by spoiling all consumers attached to the provider.
Media change event also schedules provider retaste after spoiling to probe
new media. New flag G_CF_ORPHAN was added to consumers to reflect that
consumer is in process of destruction. It allows retaste to create new
geom instance of the same class, while previous one is still dying.
 3) Modifications to some GEOM classes: DEV -- to report media change
events to devd; VFS -- to handle spoiling same as orphan to prevent
accessing replaced media. PART class already handles spoiling alike to
orphan.

Reviewed by:	silence on geom@ and scsi@
Tested by:	avg
Sponsored by:	iXsystems, Inc. / PC-BSD
MFC after:	2 months
2012-07-29 11:51:48 +00:00

739 lines
18 KiB
C

/*-
* Copyright (c) 2002 Poul-Henning Kamp
* Copyright (c) 2002 Networks Associates Technology, Inc.
* All rights reserved.
*
* This software was developed for the FreeBSD Project by Poul-Henning Kamp
* and NAI Labs, the Security Research Division of Network Associates, Inc.
* under DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the
* DARPA CHATS research program.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. The names of the authors may not be used to endorse or promote
* products derived from this software without specific prior written
* permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include "opt_geom.h"
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/sysctl.h>
#include <sys/bio.h>
#include <sys/ctype.h>
#include <sys/fcntl.h>
#include <sys/malloc.h>
#include <sys/sbuf.h>
#include <sys/sysctl.h>
#include <sys/taskqueue.h>
#include <sys/devicestat.h>
#include <machine/md_var.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <geom/geom.h>
#include <geom/geom_disk.h>
#include <geom/geom_int.h>
#include <dev/led/led.h>
struct g_disk_softc {
struct disk *dp;
struct sysctl_ctx_list sysctl_ctx;
struct sysctl_oid *sysctl_tree;
char led[64];
uint32_t state;
struct task resize_task;
};
static struct mtx g_disk_done_mtx;
static g_access_t g_disk_access;
static g_init_t g_disk_init;
static g_fini_t g_disk_fini;
static g_start_t g_disk_start;
static g_ioctl_t g_disk_ioctl;
static g_dumpconf_t g_disk_dumpconf;
static g_provgone_t g_disk_providergone;
static struct g_class g_disk_class = {
.name = "DISK",
.version = G_VERSION,
.init = g_disk_init,
.fini = g_disk_fini,
.start = g_disk_start,
.access = g_disk_access,
.ioctl = g_disk_ioctl,
.providergone = g_disk_providergone,
.dumpconf = g_disk_dumpconf,
};
SYSCTL_DECL(_kern_geom);
static SYSCTL_NODE(_kern_geom, OID_AUTO, disk, CTLFLAG_RW, 0,
"GEOM_DISK stuff");
static void
g_disk_init(struct g_class *mp __unused)
{
mtx_init(&g_disk_done_mtx, "g_disk_done", NULL, MTX_DEF);
}
static void
g_disk_fini(struct g_class *mp __unused)
{
mtx_destroy(&g_disk_done_mtx);
}
DECLARE_GEOM_CLASS(g_disk_class, g_disk);
static void __inline
g_disk_lock_giant(struct disk *dp)
{
if (dp->d_flags & DISKFLAG_NEEDSGIANT)
mtx_lock(&Giant);
}
static void __inline
g_disk_unlock_giant(struct disk *dp)
{
if (dp->d_flags & DISKFLAG_NEEDSGIANT)
mtx_unlock(&Giant);
}
static int
g_disk_access(struct g_provider *pp, int r, int w, int e)
{
struct disk *dp;
struct g_disk_softc *sc;
int error;
g_trace(G_T_ACCESS, "g_disk_access(%s, %d, %d, %d)",
pp->name, r, w, e);
g_topology_assert();
sc = pp->geom->softc;
if (sc == NULL || (dp = sc->dp) == NULL || dp->d_destroyed) {
/*
* Allow decreasing access count even if disk is not
* avaliable anymore.
*/
if (r <= 0 && w <= 0 && e <= 0)
return (0);
return (ENXIO);
}
r += pp->acr;
w += pp->acw;
e += pp->ace;
error = 0;
if ((pp->acr + pp->acw + pp->ace) == 0 && (r + w + e) > 0) {
if (dp->d_open != NULL) {
g_disk_lock_giant(dp);
error = dp->d_open(dp);
if (bootverbose && error != 0)
printf("Opened disk %s -> %d\n",
pp->name, error);
g_disk_unlock_giant(dp);
}
pp->mediasize = dp->d_mediasize;
pp->sectorsize = dp->d_sectorsize;
if (dp->d_flags & DISKFLAG_CANDELETE)
pp->flags |= G_PF_CANDELETE;
else
pp->flags &= ~G_PF_CANDELETE;
pp->stripeoffset = dp->d_stripeoffset;
pp->stripesize = dp->d_stripesize;
dp->d_flags |= DISKFLAG_OPEN;
if (dp->d_maxsize == 0) {
printf("WARNING: Disk drive %s%d has no d_maxsize\n",
dp->d_name, dp->d_unit);
dp->d_maxsize = DFLTPHYS;
}
} else if ((pp->acr + pp->acw + pp->ace) > 0 && (r + w + e) == 0) {
if (dp->d_close != NULL) {
g_disk_lock_giant(dp);
error = dp->d_close(dp);
if (error != 0)
printf("Closed disk %s -> %d\n",
pp->name, error);
g_disk_unlock_giant(dp);
}
sc->state = G_STATE_ACTIVE;
if (sc->led[0] != 0)
led_set(sc->led, "0");
dp->d_flags &= ~DISKFLAG_OPEN;
}
return (error);
}
static void
g_disk_kerneldump(struct bio *bp, struct disk *dp)
{
struct g_kerneldump *gkd;
struct g_geom *gp;
gkd = (struct g_kerneldump*)bp->bio_data;
gp = bp->bio_to->geom;
g_trace(G_T_TOPOLOGY, "g_disk_kernedump(%s, %jd, %jd)",
gp->name, (intmax_t)gkd->offset, (intmax_t)gkd->length);
if (dp->d_dump == NULL) {
g_io_deliver(bp, ENODEV);
return;
}
gkd->di.dumper = dp->d_dump;
gkd->di.priv = dp;
gkd->di.blocksize = dp->d_sectorsize;
gkd->di.maxiosize = dp->d_maxsize;
gkd->di.mediaoffset = gkd->offset;
if ((gkd->offset + gkd->length) > dp->d_mediasize)
gkd->length = dp->d_mediasize - gkd->offset;
gkd->di.mediasize = gkd->length;
g_io_deliver(bp, 0);
}
static void
g_disk_setstate(struct bio *bp, struct g_disk_softc *sc)
{
const char *cmd;
memcpy(&sc->state, bp->bio_data, sizeof(sc->state));
if (sc->led[0] != 0) {
switch (sc->state) {
case G_STATE_FAILED:
cmd = "1";
break;
case G_STATE_REBUILD:
cmd = "f5";
break;
case G_STATE_RESYNC:
cmd = "f1";
break;
default:
cmd = "0";
break;
}
led_set(sc->led, cmd);
}
g_io_deliver(bp, 0);
}
static void
g_disk_done(struct bio *bp)
{
struct bio *bp2;
struct disk *dp;
struct g_disk_softc *sc;
/* See "notes" for why we need a mutex here */
/* XXX: will witness accept a mix of Giant/unGiant drivers here ? */
mtx_lock(&g_disk_done_mtx);
bp->bio_completed = bp->bio_length - bp->bio_resid;
bp2 = bp->bio_parent;
if (bp2->bio_error == 0)
bp2->bio_error = bp->bio_error;
bp2->bio_completed += bp->bio_completed;
if ((bp->bio_cmd & (BIO_READ|BIO_WRITE|BIO_DELETE)) != 0 &&
(sc = bp2->bio_to->geom->softc) != NULL &&
(dp = sc->dp) != NULL) {
devstat_end_transaction_bio(dp->d_devstat, bp);
}
g_destroy_bio(bp);
bp2->bio_inbed++;
if (bp2->bio_children == bp2->bio_inbed) {
bp2->bio_resid = bp2->bio_bcount - bp2->bio_completed;
g_io_deliver(bp2, bp2->bio_error);
}
mtx_unlock(&g_disk_done_mtx);
}
static int
g_disk_ioctl(struct g_provider *pp, u_long cmd, void * data, int fflag, struct thread *td)
{
struct g_geom *gp;
struct disk *dp;
struct g_disk_softc *sc;
int error;
gp = pp->geom;
sc = gp->softc;
dp = sc->dp;
if (dp->d_ioctl == NULL)
return (ENOIOCTL);
g_disk_lock_giant(dp);
error = dp->d_ioctl(dp, cmd, data, fflag, td);
g_disk_unlock_giant(dp);
return (error);
}
static void
g_disk_start(struct bio *bp)
{
struct bio *bp2, *bp3;
struct disk *dp;
struct g_disk_softc *sc;
int error;
off_t off;
sc = bp->bio_to->geom->softc;
if (sc == NULL || (dp = sc->dp) == NULL || dp->d_destroyed) {
g_io_deliver(bp, ENXIO);
return;
}
error = EJUSTRETURN;
switch(bp->bio_cmd) {
case BIO_DELETE:
if (!(dp->d_flags & DISKFLAG_CANDELETE)) {
error = EOPNOTSUPP;
break;
}
/* fall-through */
case BIO_READ:
case BIO_WRITE:
off = 0;
bp3 = NULL;
bp2 = g_clone_bio(bp);
if (bp2 == NULL) {
error = ENOMEM;
break;
}
do {
bp2->bio_offset += off;
bp2->bio_length -= off;
bp2->bio_data += off;
if (bp2->bio_length > dp->d_maxsize) {
/*
* XXX: If we have a stripesize we should really
* use it here.
*/
bp2->bio_length = dp->d_maxsize;
off += dp->d_maxsize;
/*
* To avoid a race, we need to grab the next bio
* before we schedule this one. See "notes".
*/
bp3 = g_clone_bio(bp);
if (bp3 == NULL)
bp->bio_error = ENOMEM;
}
bp2->bio_done = g_disk_done;
bp2->bio_pblkno = bp2->bio_offset / dp->d_sectorsize;
bp2->bio_bcount = bp2->bio_length;
bp2->bio_disk = dp;
devstat_start_transaction_bio(dp->d_devstat, bp2);
g_disk_lock_giant(dp);
dp->d_strategy(bp2);
g_disk_unlock_giant(dp);
bp2 = bp3;
bp3 = NULL;
} while (bp2 != NULL);
break;
case BIO_GETATTR:
/* Give the driver a chance to override */
if (dp->d_getattr != NULL) {
if (bp->bio_disk == NULL)
bp->bio_disk = dp;
error = dp->d_getattr(bp);
if (error != -1)
break;
error = EJUSTRETURN;
}
if (g_handleattr_int(bp, "GEOM::candelete",
(dp->d_flags & DISKFLAG_CANDELETE) != 0))
break;
else if (g_handleattr_int(bp, "GEOM::fwsectors",
dp->d_fwsectors))
break;
else if (g_handleattr_int(bp, "GEOM::fwheads", dp->d_fwheads))
break;
else if (g_handleattr_off_t(bp, "GEOM::frontstuff", 0))
break;
else if (g_handleattr_str(bp, "GEOM::ident", dp->d_ident))
break;
else if (g_handleattr(bp, "GEOM::hba_vendor",
&dp->d_hba_vendor, 2))
break;
else if (g_handleattr(bp, "GEOM::hba_device",
&dp->d_hba_device, 2))
break;
else if (g_handleattr(bp, "GEOM::hba_subvendor",
&dp->d_hba_subvendor, 2))
break;
else if (g_handleattr(bp, "GEOM::hba_subdevice",
&dp->d_hba_subdevice, 2))
break;
else if (!strcmp(bp->bio_attribute, "GEOM::kerneldump"))
g_disk_kerneldump(bp, dp);
else if (!strcmp(bp->bio_attribute, "GEOM::setstate"))
g_disk_setstate(bp, sc);
else
error = ENOIOCTL;
break;
case BIO_FLUSH:
g_trace(G_T_TOPOLOGY, "g_disk_flushcache(%s)",
bp->bio_to->name);
if (!(dp->d_flags & DISKFLAG_CANFLUSHCACHE)) {
error = EOPNOTSUPP;
break;
}
bp2 = g_clone_bio(bp);
if (bp2 == NULL) {
g_io_deliver(bp, ENOMEM);
return;
}
bp2->bio_done = g_disk_done;
bp2->bio_disk = dp;
g_disk_lock_giant(dp);
dp->d_strategy(bp2);
g_disk_unlock_giant(dp);
break;
default:
error = EOPNOTSUPP;
break;
}
if (error != EJUSTRETURN)
g_io_deliver(bp, error);
return;
}
static void
g_disk_dumpconf(struct sbuf *sb, const char *indent, struct g_geom *gp, struct g_consumer *cp, struct g_provider *pp)
{
struct disk *dp;
struct g_disk_softc *sc;
sc = gp->softc;
if (sc == NULL || (dp = sc->dp) == NULL)
return;
if (indent == NULL) {
sbuf_printf(sb, " hd %u", dp->d_fwheads);
sbuf_printf(sb, " sc %u", dp->d_fwsectors);
return;
}
if (pp != NULL) {
sbuf_printf(sb, "%s<fwheads>%u</fwheads>\n",
indent, dp->d_fwheads);
sbuf_printf(sb, "%s<fwsectors>%u</fwsectors>\n",
indent, dp->d_fwsectors);
sbuf_printf(sb, "%s<ident>%s</ident>\n", indent, dp->d_ident);
sbuf_printf(sb, "%s<descr>%s</descr>\n", indent, dp->d_descr);
}
}
static void
g_disk_resize_task(void *context, int pending)
{
struct g_geom *gp;
struct g_provider *pp;
struct disk *dp;
struct g_disk_softc *sc;
sc = (struct g_disk_softc *)context;
dp = sc->dp;
gp = dp->d_geom;
LIST_FOREACH(pp, &gp->provider, provider) {
if (pp->sectorsize != 0 &&
pp->sectorsize != dp->d_sectorsize)
g_wither_provider(pp, ENXIO);
else
g_resize_provider(pp, dp->d_mediasize);
}
}
static void
g_disk_create(void *arg, int flag)
{
struct g_geom *gp;
struct g_provider *pp;
struct disk *dp;
struct g_disk_softc *sc;
char tmpstr[80];
if (flag == EV_CANCEL)
return;
g_topology_assert();
dp = arg;
sc = g_malloc(sizeof(*sc), M_WAITOK | M_ZERO);
sc->dp = dp;
gp = g_new_geomf(&g_disk_class, "%s%d", dp->d_name, dp->d_unit);
gp->softc = sc;
pp = g_new_providerf(gp, "%s", gp->name);
pp->mediasize = dp->d_mediasize;
pp->sectorsize = dp->d_sectorsize;
if (dp->d_flags & DISKFLAG_CANDELETE)
pp->flags |= G_PF_CANDELETE;
pp->stripeoffset = dp->d_stripeoffset;
pp->stripesize = dp->d_stripesize;
if (bootverbose)
printf("GEOM: new disk %s\n", gp->name);
sysctl_ctx_init(&sc->sysctl_ctx);
snprintf(tmpstr, sizeof(tmpstr), "GEOM disk %s", gp->name);
sc->sysctl_tree = SYSCTL_ADD_NODE(&sc->sysctl_ctx,
SYSCTL_STATIC_CHILDREN(_kern_geom_disk), OID_AUTO, gp->name,
CTLFLAG_RD, 0, tmpstr);
if (sc->sysctl_tree != NULL) {
snprintf(tmpstr, sizeof(tmpstr),
"kern.geom.disk.%s.led", gp->name);
TUNABLE_STR_FETCH(tmpstr, sc->led, sizeof(sc->led));
SYSCTL_ADD_STRING(&sc->sysctl_ctx,
SYSCTL_CHILDREN(sc->sysctl_tree), OID_AUTO, "led",
CTLFLAG_RW | CTLFLAG_TUN, sc->led, sizeof(sc->led),
"LED name");
}
TASK_INIT(&sc->resize_task, 0, g_disk_resize_task, sc);
pp->private = sc;
dp->d_geom = gp;
g_error_provider(pp, 0);
}
/*
* We get this callback after all of the consumers have gone away, and just
* before the provider is freed. If the disk driver provided a d_gone
* callback, let them know that it is okay to free resources -- they won't
* be getting any more accesses from GEOM.
*/
static void
g_disk_providergone(struct g_provider *pp)
{
struct disk *dp;
struct g_disk_softc *sc;
sc = (struct g_disk_softc *)pp->geom->softc;
/*
* If the softc is already NULL, then we've probably been through
* g_disk_destroy already; there is nothing for us to do anyway.
*/
if (sc == NULL)
return;
dp = sc->dp;
if (dp->d_gone != NULL)
dp->d_gone(dp);
}
static void
g_disk_destroy(void *ptr, int flag)
{
struct disk *dp;
struct g_geom *gp;
struct g_disk_softc *sc;
g_topology_assert();
dp = ptr;
gp = dp->d_geom;
if (gp != NULL) {
sc = gp->softc;
if (sc->sysctl_tree != NULL) {
sysctl_ctx_free(&sc->sysctl_ctx);
sc->sysctl_tree = NULL;
}
if (sc->led[0] != 0) {
led_set(sc->led, "0");
sc->led[0] = 0;
}
g_free(sc);
gp->softc = NULL;
g_wither_geom(gp, ENXIO);
}
g_free(dp);
}
/*
* We only allow printable characters in disk ident,
* the rest is converted to 'x<HH>'.
*/
static void
g_disk_ident_adjust(char *ident, size_t size)
{
char *p, tmp[4], newid[DISK_IDENT_SIZE];
newid[0] = '\0';
for (p = ident; *p != '\0'; p++) {
if (isprint(*p)) {
tmp[0] = *p;
tmp[1] = '\0';
} else {
snprintf(tmp, sizeof(tmp), "x%02hhx",
*(unsigned char *)p);
}
if (strlcat(newid, tmp, sizeof(newid)) >= sizeof(newid))
break;
}
bzero(ident, size);
strlcpy(ident, newid, size);
}
struct disk *
disk_alloc(void)
{
return (g_malloc(sizeof(struct disk), M_WAITOK | M_ZERO));
}
void
disk_create(struct disk *dp, int version)
{
if (version != DISK_VERSION_02) {
printf("WARNING: Attempt to add disk %s%d %s",
dp->d_name, dp->d_unit,
" using incompatible ABI version of disk(9)\n");
printf("WARNING: Ignoring disk %s%d\n",
dp->d_name, dp->d_unit);
return;
}
KASSERT(dp->d_strategy != NULL, ("disk_create need d_strategy"));
KASSERT(dp->d_name != NULL, ("disk_create need d_name"));
KASSERT(*dp->d_name != 0, ("disk_create need d_name"));
KASSERT(strlen(dp->d_name) < SPECNAMELEN - 4, ("disk name too long"));
if (dp->d_devstat == NULL)
dp->d_devstat = devstat_new_entry(dp->d_name, dp->d_unit,
dp->d_sectorsize, DEVSTAT_ALL_SUPPORTED,
DEVSTAT_TYPE_DIRECT, DEVSTAT_PRIORITY_MAX);
dp->d_geom = NULL;
g_disk_ident_adjust(dp->d_ident, sizeof(dp->d_ident));
g_post_event(g_disk_create, dp, M_WAITOK, dp, NULL);
}
void
disk_destroy(struct disk *dp)
{
g_cancel_event(dp);
dp->d_destroyed = 1;
if (dp->d_devstat != NULL)
devstat_remove_entry(dp->d_devstat);
g_post_event(g_disk_destroy, dp, M_WAITOK, NULL);
}
void
disk_gone(struct disk *dp)
{
struct g_geom *gp;
struct g_provider *pp;
gp = dp->d_geom;
if (gp != NULL)
LIST_FOREACH(pp, &gp->provider, provider)
g_wither_provider(pp, ENXIO);
}
void
disk_attr_changed(struct disk *dp, const char *attr, int flag)
{
struct g_geom *gp;
struct g_provider *pp;
gp = dp->d_geom;
if (gp != NULL)
LIST_FOREACH(pp, &gp->provider, provider)
(void)g_attr_changed(pp, attr, flag);
}
void
disk_media_changed(struct disk *dp, int flag)
{
struct g_geom *gp;
struct g_provider *pp;
gp = dp->d_geom;
if (gp != NULL) {
LIST_FOREACH(pp, &gp->provider, provider)
g_media_changed(pp, flag);
}
}
void
disk_media_gone(struct disk *dp, int flag)
{
struct g_geom *gp;
struct g_provider *pp;
gp = dp->d_geom;
if (gp != NULL) {
LIST_FOREACH(pp, &gp->provider, provider)
g_media_gone(pp, flag);
}
}
void
disk_resize(struct disk *dp)
{
struct g_geom *gp;
struct g_disk_softc *sc;
int error;
gp = dp->d_geom;
if (gp == NULL)
return;
sc = gp->softc;
error = taskqueue_enqueue(taskqueue_thread, &sc->resize_task);
KASSERT(error == 0, ("taskqueue_enqueue(9) failed."));
}
static void
g_kern_disks(void *p, int flag __unused)
{
struct sbuf *sb;
struct g_geom *gp;
char *sp;
sb = p;
sp = "";
g_topology_assert();
LIST_FOREACH(gp, &g_disk_class.geom, geom) {
sbuf_printf(sb, "%s%s", sp, gp->name);
sp = " ";
}
sbuf_finish(sb);
}
static int
sysctl_disks(SYSCTL_HANDLER_ARGS)
{
int error;
struct sbuf *sb;
sb = sbuf_new_auto();
g_waitfor_event(g_kern_disks, sb, M_WAITOK, NULL);
error = SYSCTL_OUT(req, sbuf_data(sb), sbuf_len(sb) + 1);
sbuf_delete(sb);
return error;
}
SYSCTL_PROC(_kern, OID_AUTO, disks,
CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_MPSAFE, NULL, 0,
sysctl_disks, "A", "names of available disks");