Always send EOI. We can't feasibly share interrupts (since we have no

clue what the "previous" interrupt handler will do, which could range
from "just an iret" to "disable the interrupt"), and that means that
we have to take responsibility for ACKing all interrupts.  Joy.

src/arch/i386/drivers/net/undinet.c

 		/* Do nothing unless ISR has been triggered */
 		if ( ! undinet_isr_triggered() )
 			return;
-		
+
 		/* See if this was our interrupt */
 		memset ( &undi_isr, 0, sizeof ( undi_isr ) );
 		undi_isr.FuncFlag = PXENV_UNDI_ISR_IN_START;
 		if ( ( rc = undinet_call ( undinic, PXENV_UNDI_ISR, &undi_isr,
 					   sizeof ( undi_isr ) ) ) != 0 )
 			return;
+
+		/* Send EOI to the PIC.  In an ideal world, we'd do
+		 * this only for interrupts which the UNDI stack
+		 * reports as "ours".  However, since we don't (can't)
+		 * chain to the previous interrupt handler, we have to
+		 * acknowledge all interrupts.  See undinet_hook_isr()
+		 * for more background.
+		 */
+		send_eoi ( undinic->irq );
+
+		/* If this wasn't our interrupt, exit now */
 		if ( undi_isr.FuncFlag != PXENV_UNDI_ISR_OUT_OURS )
 			return;
 		
-		/* Send EOI */
-		send_eoi ( undinic->irq );
-
 		/* Start ISR processing */
 		undinic->isr_processing = 1;
 		undi_isr.FuncFlag = PXENV_UNDI_ISR_IN_PROCESS;