cvs commit: src/sys/sys socketvar.h

Peter Jeremy peterjeremy at
Tue Jul 3 19:52:30 UTC 2007

On 2007-Jul-03 10:14:13 +0000, Robert Watson <rwatson at> wrote:
>  Fix a bug in sblock() that has existed since revision 1.1 from BSD:
>  correctly return an error if M_NOWAIT is passed to sblock() and the
>  operation might block.  This remarkably subtle macro bug appears to
>  be responsible for quite a few undiagnosed socket buffer corruption
>  and mbuf-related kernel panics.

This bug would appear to be a classic example of the dangers of trying
to force force multiple C statements into a single statement.  IMHO,
it (and many of the other macros in socketvar.h) should be inline
functions, rather than macros.

IMHO, the following is far more legible:

static __inline int
sblock(struct sockbuf *sb, int wf)
	if (sb->sb_flags & SB_LOCK)
		return ((wf == M_WAITOK) ? sb_lock(sb) : EWOULDBLOCK);
	else {
		sb->sb_flags |= SB_LOCK;
		return (0);

Peter Jeremy
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