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From: "Christian S.J. Peron" <csjp@FreeBSD.org>
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Subject: PERFORCE change 114152 for review
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http://perforce.freebsd.org/chv.cgi?CH=114152

Change 114152 by csjp@csjp_rnd01 on 2007/02/07 05:01:04

	Annotate that in the future before we issue wakesup, we might do something like:
	
	(1) Check to see if this descriptor is operating in immediate mode
	(2) Check to see if the holder buffer is NULL
	(3) Check to see if we are waking up any sleepers
	
	We do not need to check the store buffer, as the fact that it has data in it
	at this point in the code is invariant.
	
	If the following conditions are true, then rotate the buffer. This will save
	userspace from issuing an ioctl(2) potentially per wakeup.

Affected files ...

.. //depot/projects/zcopybpf/src/sys/net/bpf.c#14 edit

Differences ...

==== //depot/projects/zcopybpf/src/sys/net/bpf.c#14 (text+ko) ====

@@ -1760,6 +1760,11 @@
 	(*cpfn)(d, d->bd_sbuf, curlen + hdrlen, pkt, hdr.bh_caplen);
 	d->bd_slen = curlen + totlen;
 
+	/*
+	 * XXXCSJP we could probably save a syscall per wakeup if we check the
+	 * d->bd_immediate flag, hold buffer status and rotate the buffers
+	 * before the wakeup.
+	 */
 	if (do_wakeup)
 		bpf_wakeup(d);
 }