kern/84823: [PATCH] bpf in non-blocking mode is broken

[Rudolf Cejka]

>Number:         84823
>Category:       kern
>Synopsis:       [PATCH] bpf in non-blocking mode is broken
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Thu Aug 11 22:30:08 GMT 2005
>Closed-Date:
>Last-Modified:
>Originator:     Rudolf Cejka
>Release:        FreeBSD 5.3-STABLE i386
>Organization:
FIT, Brno University of Technology, Czech Republic
>Environment:

  Any FreeBSD since Dec 17 2000 with sys/net/bpf.c >= 1.72.

>Description:

  When bpf is in non-blocking mode, it always returns EWOULDBLOCK - it
  never returns any data. The bpf is broken since following commit:

  : Revision 1.72, Sun Dec 17 20:50:22 2000 UTC (4 years, 7 months ago)
  :
  : Fix bug: a read() on a bpf device which was in non-blocking mode
  : and had no data available returned 0.  Now it returns -1 with errno
  : set to EWOULDBLOCK (== EAGAIN) as it should.  This fix makes the bpf
  : device usable in threaded programs.

>How-To-Repeat:
>Fix:

  Following patch should fix the problem:

--- sys/net/bpf.c.orig	Thu Aug 11 23:24:42 2005
+++ sys/net/bpf.c	Thu Aug 11 23:27:10 2005
@@ -489,8 +489,13 @@
 		}
 
 		if (ioflag & O_NONBLOCK) {
-			BPFD_UNLOCK(d);
-			return (EWOULDBLOCK);
+			if (d->bd_slen == 0) {
+				BPFD_UNLOCK(d);
+				return (EWOULDBLOCK);
+			} else {
+				ROTATE_BUFFERS(d);
+				break;
+			}
 		}
 		error = msleep(d, &d->bd_mtx, PRINET|PCATCH,
 		     "bpf", d->bd_rtout);
>Release-Note:
>Audit-Trail:
>Unformatted: