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, 1 insertions, 0 deletions

diff --git a/sys/net/if.h b/sys/net/if.h
index 1dab8c0..084fc9d 100644
--- a/sys/net/if.h
+++ b/sys/net/if.h
@@ -126,6 +126,7 @@ struct if_data {
 #define	IFF_PPROMISC	0x20000		/* user-requested promisc mode */
 #define	IFF_MONITOR	0x40000		/* user-requested monitor mode */
 #define	IFF_STATICARP	0x80000		/* static ARP */
+#define	IFF_NEEDSGIANT	0x100000	/* hold Giant over if_start calls */
 
 /* flags set internally only: */
 #define	IFF_CANTCHANGE \