netdev - [PATCH 01/21] netfilter: nft_bitwise: correct uapi header comment.

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Message-Id: <20200118201417.334111-2-pablo@netfilter.org>
Date:   Sat, 18 Jan 2020 21:13:57 +0100
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     netfilter-devel@...r.kernel.org
Cc:     davem@...emloft.net, netdev@...r.kernel.org
Subject: [PATCH 01/21] netfilter: nft_bitwise: correct uapi header comment.

From: Jeremy Sowden <jeremy@...zel.net>

The comment documenting how bitwise expressions work includes a table
which summarizes the mask and xor arguments combined to express the
supported boolean operations.  However, the row for OR:

 mask    xor
 0       x

is incorrect.

  dreg = (sreg & 0) ^ x

is not equivalent to:

  dreg = sreg | x

What the code actually does is:

  dreg = (sreg & ~x) ^ x

Update the documentation to match.

Signed-off-by: Jeremy Sowden <jeremy@...zel.net>
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
---
 include/uapi/linux/netfilter/nf_tables.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/uapi/linux/netfilter/nf_tables.h b/include/uapi/linux/netfilter/nf_tables.h
index e237ecbdcd8a..dd4611767933 100644
--- a/include/uapi/linux/netfilter/nf_tables.h
+++ b/include/uapi/linux/netfilter/nf_tables.h
@@ -501,7 +501,7 @@ enum nft_immediate_attributes {
  *
  * 		mask	xor
  * NOT:		1	1
- * OR:		0	x
+ * OR:		~x	x
  * XOR:		1	x
  * AND:		x	0
  */
-- 
2.11.0