replace IFF_OACTIVE manipulation with mpsafe operations.

there are two things shared between the network stack and drivers
in the send path: the send queue and the IFF_OACTIVE flag. the send
queue is now protected by a mutex. this diff makes the oactive
functionality mpsafe too.

IFF_OACTIVE is part of if_flags. there are two problems with that.
firstly, if_flags is a short and we dont have any MI atomic operations
to manipulate a short. secondly, while we could make the IFF_OACTIVE
operates mpsafe, all changes to other flags would have to be made
safe at the same time, otherwise a read-modify-write cycle on their
updates could clobber the oactive change.

instead, this moves the oactive mark into struct ifqueue and provides
an API for changing it. there's ifq_set_oactive, ifq_clr_oactive,
and ifq_is_oactive. these are modelled on ifsq_set_oactive,
ifsq_clr_oactive, and ifsq_is_oactive in dragonflybsd.

this diff includes changes to all the drivers manipulating IFF_OACTIVE
to now use the ifsq_{set,clr_is}_oactive API too.

ok kettenis@ mpi@ jmatthew@ deraadt@

1 files changed, 36 insertions, 4 deletions

diff --git a/share/man/man9/ifq_enqueue.9 b/share/man/man9/ifq_enqueue.9
index d3509cbbf5d..03c5909b0ca 100644
--- a/share/man/man9/ifq_enqueue.9
+++ b/share/man/man9/ifq_enqueue.9
@@ -1,4 +1,4 @@
-.\"     $OpenBSD: ifq_enqueue.9,v 1.3 2015/11/23 11:07:58 jmc Exp $
+.\"     $OpenBSD: ifq_enqueue.9,v 1.4 2015/11/25 03:09:57 dlg Exp $
 .\"
 .\"  Copyright (c) 2015 David Gwynne <dlg@openbsd.org>
 .\"
@@ -14,7 +14,7 @@
 .\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 .\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 .\"
-.Dd $Mdocdate: November 23 2015 $
+.Dd $Mdocdate: November 25 2015 $
 .Dt IFQ_ENQUEUE 9
 .Os
 .Sh NAME
@@ -22,7 +22,10 @@
 .Nm ifq_dequeue ,
 .Nm ifq_purge ,
 .Nm ifq_len ,
-.Nm ifq_empty
+.Nm ifq_empty ,
+.Nm ifq_set_oactive ,
+.Nm ifq_clr_oactive ,
+.Nm ifq_is_oactive
 .Nd interface send queue API
 .Sh SYNOPSIS
 .In net/if_var.h
@@ -36,6 +39,12 @@
 .Fn ifq_len "struct ifqueue *ifq"
 .Ft unsigned int
 .Fn ifq_empty "struct ifqueue *ifq"
+.Ft void
+.Fn ifq_set_oactive "struct ifqueue *ifq"
+.Ft void
+.Fn ifq_clr_oactive "struct ifqueue *ifq"
+.Ft unsigned int
+.Fn ifq_is_oactive "struct ifqueue *ifq"
 .Sh DESCRIPTION
 The ifqueue API provides implementions of data structures and
 operations for the network stack to queue mbufs for a network driver
@@ -72,14 +81,33 @@ or
 Return if the interface send queue
 .Fa ifq
 is empty.
+.It Fn ifq_set_oactive "struct ifqueue *ifq"
+.Fn ifq_set_oactive
+is called by the relevant driver to mark the hardware associated
+with the interface send queue
+.Fa ifq
+as unable to transmit more packets.
+.It Fn ifq_clr_oactive "struct ifqueue *ifq"
+.Fn ifq_clr_oactive
+is called by the relevant driver to clear the "active" mark on the
+hardware associated with the interface send queue
+.Fa ifq ,
+meaning it is now able to transmit packets.
+.It Fn ifq_is_oactive "struct ifqueue *ifq"
+Return if the hardware associated with the interface send queue
+.Fa ifq
+is unable to transmit more packets.
 .El
 .Sh CONTEXT
 .Fn ifq_enqueue ,
 .Fn ifq_dequeue ,
 .Fn ifq_purge ,
 .Fn ifq_len ,
+.Fn ifq_empty ,
+.Fn ifq_set_oactive ,
+.Fn ifq_clr_oactive ,
 and
-.Fn ifq_empty
+.Fn ifq_is_oactive
 can be called during autoconf, from process context, or from interrupt context.
 .Sh RETURN VALUES
 .Fn ifq_enqueue
@@ -99,6 +127,10 @@ returns the number of mbufs on the queue.
 .Pp
 .Fn ifq_empty
 returns a non-zero value if the queue is empty, otherwise 0.
+.Pp
+.Fn ifq_is_oactive
+returns a non-zero value if the hardware associated with the interface
+send queue is unable to transmit more packets, otherwise 0.
 .Sh SEE ALSO
 .Xr ifq_deq_begin 9 ,
 .Xr m_freem 9