PERFORCE change 137253 for review
Robert Watson
rwatson at FreeBSD.org
Sun Mar 9 19:58:47 UTC 2008
http://perforce.freebsd.org/chv.cgi?CH=137253
Change 137253 by rwatson at rwatson_cinnamon on 2008/03/09 19:58:30
Add a note of caution on memory ordering, etc, to bpf.h when
describing the shared memory header.
Affected files ...
.. //depot/projects/zcopybpf/src/sys/net/bpf.h#25 edit
Differences ...
==== //depot/projects/zcopybpf/src/sys/net/bpf.h#25 (text+ko) ====
@@ -177,7 +177,10 @@
/*
* When using zero-copy BPF buffers, a shared memory header is present
* allowing the kernel BPF implementation and user process to synchronize
- * without using system calls. This structure defines that header.
+ * without using system calls. This structure defines that header. When
+ * accessing these fields, appropriate atomic operation and memory barriers
+ * are required in order not to see stale or out-of-order data; see bpf(4)
+ * for reference code to access these fields from userspace.
*
* The layout of this structure is critical, and must not be changed; if must
* fit in a single page on all architectures.
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