Add a new network interface flag, IFF_NEEDSGIANT, which will allow

device drivers to declare that the ifp->if_start() method implemented
by the driver requires Giant in order to operate correctly.

Add a 'struct task' to 'struct ifnet' that can be used to execute a
deferred ifp->if_start() in the event that if_start needs to be called
in a Giant-free environment.  To do this, introduce if_start(), a
wrapper function for ifp->if_start().  If the interface can run MPSAFE,
it directly dispatches into the interface start routine.  If it can't
run MPSAFE, we're running with debug.mpsafenet != 0, and Giant isn't
currently held, the task is queued to execute in a swi holding Giant
via if_start_deferred().

Modify if_handoff() to use if_start() instead of direct dispatch.
Modify 802.11 to use if_start() instead of direct dispatch.

This is intended to provide increased compatibility for non-MPSAFE
network device drivers in the presence of Giant-free operation via
asynchronous dispatch.  However, this commit does not mark any network
interfaces as IFF_NEEDSGIANT.

1 files changed, 2 insertions, 0 deletions

diff --git a/sys/net/if_ethersubr.c b/sys/net/if_ethersubr.c
index fb10e01..080dcfb 100644
--- a/sys/net/if_ethersubr.c
+++ b/sys/net/if_ethersubr.c
@@ -888,6 +888,8 @@ ether_ifattach(struct ifnet *ifp, const u_int8_t *llc)
 			break; 
 	if (i != ifp->if_addrlen)
 		if_printf(ifp, "Ethernet address: %6D\n", llc, ":");
+	if (debug_mpsafenet && (ifp->if_flags & IFF_NEEDSGIANT) != 0)
+		if_printf(ifp, "if_start running deferred for Giant\n");
 }
 
 /*