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if_tuntap: add a busy/unbusy mechanism, replace destroy OPEN check

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A future commit will create device aliases when a tuntap device is renamed
so that it's still easily found in /dev after the rename.  Said mechanism
will want to keep the tun alive long enough to either realize that it's
about to go away or complete the alias creation, even if the alias is about
to get destroyed.

While we're introducing it, using it to prevent open devices from going away
makes plenty of sense and keeps the logic on waking up tun_destroy clean, so
we don't have multiple places trying to cv_broadcast unless it's still in
use elsewhere.
This commit is contained in:
Kyle Evans 2019-10-03 17:46:27 +00:00
parent ee0ee18c9c
commit c4cad1549e
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=353056
1 changed files with 72 additions and 4 deletions
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76
sys/net/if_tuntap.c
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@ -131,13 +131,15 @@ struct tuntap_softc {
struct mtx tun_mtx; /* softc field mutex */
struct cv tun_cv; /* for ref'd dev destroy */
struct ether_addr tun_ether; /* remote address */
int tun_busy; /* busy count */
};
#define TUN2IFP(sc) ((sc)->tun_ifp)
#define TUNDEBUG if (tundebug) if_printf
#define TUN_LOCK(tp) mtx_lock(&(tp)->tun_mtx)
#define TUN_UNLOCK(tp) mtx_unlock(&(tp)->tun_mtx)
#define TUN_LOCK(tp) mtx_lock(&(tp)->tun_mtx)
#define TUN_UNLOCK(tp) mtx_unlock(&(tp)->tun_mtx)
#define TUN_LOCK_ASSERT(tp) mtx_assert(&(tp)->tun_mtx, MA_OWNED);
#define TUN_VMIO_FLAG_MASK 0x0fff
@ -182,6 +184,11 @@ SYSCTL_INT(_net_link_tap, OID_AUTO, devfs_cloning, CTLFLAG_RWTUN, &tapdclone, 0,
"Enable legacy devfs interface creation");
SYSCTL_INT(_net_link_tap, OID_AUTO, debug, CTLFLAG_RW, &tundebug, 0, "");
static int tun_busy_locked(struct tuntap_softc *tp);
static void tun_unbusy_locked(struct tuntap_softc *tp);
static int tun_busy(struct tuntap_softc *tp);
static void tun_unbusy(struct tuntap_softc *tp);
static int tuntap_name2info(const char *name, int *unit, int *flags);
static void tunclone(void *arg, struct ucred *cred, char *name,
int namelen, struct cdev **dev);
@ -303,6 +310,65 @@ VNET_DEFINE_STATIC(SLIST_HEAD(, tuntap_driver_cloner), tuntap_driver_cloners) =
#define V_tuntap_driver_cloners VNET(tuntap_driver_cloners)
/*
* Mechanism for marking a tunnel device as busy so that we can safely do some
* orthogonal operations (such as operations on devices) without racing against
* tun_destroy. tun_destroy will wait on the condvar if we're at all busy or
* open, to be woken up when the condition is alleviated.
*/
static int
tun_busy_locked(struct tuntap_softc *tp)
{
TUN_LOCK_ASSERT(tp);
if ((tp->tun_flags & TUN_DYING) != 0) {
/*
* Perhaps unintuitive, but the device is busy going away.
* Other interpretations of EBUSY from tun_busy make little
* sense, since making a busy device even more busy doesn't
* sound like a problem.
*/
return (EBUSY);
}
++tp->tun_busy;
return (0);
}
static void
tun_unbusy_locked(struct tuntap_softc *tp)
{
TUN_LOCK_ASSERT(tp);
KASSERT(tp->tun_busy != 0, ("tun_unbusy: called for non-busy tunnel"));
--tp->tun_busy;
/* Wake up anything that may be waiting on our busy tunnel. */
if (tp->tun_busy == 0)
cv_broadcast(&tp->tun_cv);
}
static int
tun_busy(struct tuntap_softc *tp)
{
int ret;
TUN_LOCK(tp);
ret = tun_busy_locked(tp);
TUN_UNLOCK(tp);
return (ret);
}
static void
tun_unbusy(struct tuntap_softc *tp)
{
TUN_LOCK(tp);
tun_unbusy_locked(tp);
TUN_UNLOCK(tp);
}
/*
* Sets unit and/or flags given the device name. Must be called with correct
* vnet context.
@ -531,7 +597,7 @@ tun_destroy(struct tuntap_softc *tp)
TUN_LOCK(tp);
tp->tun_flags |= TUN_DYING;
if ((tp->tun_flags & TUN_OPEN) != 0)
if (tp->tun_busy != 0)
cv_wait_unlock(&tp->tun_cv, &tp->tun_mtx);
else
TUN_UNLOCK(tp);
@ -885,6 +951,8 @@ tunopen(struct cdev *dev, int flag, int mode, struct thread *td)
return (EBUSY);
}
error = tun_busy_locked(tp);
KASSERT(error == 0, ("Must be able to busy an unopen tunnel"));
ifp = TUN2IFP(tp);
if ((tp->tun_flags & TUN_L2) != 0) {
@ -988,7 +1056,7 @@ tunclose(struct cdev *dev, int foo, int bar, struct thread *td)
tp->tun_flags &= ~TUN_OPEN;
tp->tun_pid = 0;
cv_broadcast(&tp->tun_cv);
tun_unbusy_locked(tp);
TUN_UNLOCK(tp);
return (0);
}