netdev - [PATCH net-next 3/3] net/act_pedit: Introduce 'add' operation

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Date:   Wed, 30 Nov 2016 11:09:28 +0200
From:   Amir Vadai <amir@...ai.me>
To:     "David S. Miller" <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, Jamal Hadi Salim <jhs@...atatu.com>,
        Or Gerlitz <ogerlitz@...lanox.com>,
        Hadar Har-Zion <hadarh@...lanox.com>,
        Amir Vadai <amir@...ai.me>
Subject: [PATCH net-next 3/3] net/act_pedit: Introduce 'add' operation

This command could be useful to inc/dec fields.

For example, to forward any TCP packet and decrease its TTL:
$ tc filter add dev enp0s9 protocol ip parent ffff: \
    flower ip_proto tcp \
    action pedit munge ip ttl add 0xff pipe \
    action mirred egress redirect dev veth0

In the example above, adding 0xff to this u8 field is actually
decreasing it by one, since the operation is masked.

Signed-off-by: Amir Vadai <amir@...ai.me>
---
 include/uapi/linux/tc_act/tc_pedit.h | 10 ++++++++++
 net/sched/act_pedit.c                | 16 +++++++++++++++-
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/tc_act/tc_pedit.h b/include/uapi/linux/tc_act/tc_pedit.h
index 604e6729ad38..80028cd0bb1b 100644
--- a/include/uapi/linux/tc_act/tc_pedit.h
+++ b/include/uapi/linux/tc_act/tc_pedit.h
@@ -35,8 +35,13 @@ struct tc_pedit_sel {
 #define PEDIT_TYPE_SHIFT 24
 #define PEDIT_TYPE_MASK 0xff
 
+#define PEDIT_CMD_SHIFT 16
+#define PEDIT_CMD_MASK 0xff
+
 #define PEDIT_TYPE_GET(_val) \
 	(((_val) >> PEDIT_TYPE_SHIFT) & PEDIT_TYPE_MASK)
+#define PEDIT_CMD_GET(_val) \
+	(((_val) >> PEDIT_CMD_SHIFT) & PEDIT_CMD_MASK)
 #define PEDIT_SHIFT_GET(_val) ((_val) & 0xff)
 
 enum pedit_header_type {
@@ -49,4 +54,9 @@ enum pedit_header_type {
 	PEDIT_HDR_TYPE_UDP = 5,
 };
 
+enum pedit_cmd {
+	PEDIT_CMD_SET = 0,
+	PEDIT_CMD_ADD = 1,
+};
+
 #endif
diff --git a/net/sched/act_pedit.c b/net/sched/act_pedit.c
index 4b9c7184c752..aa137d51bf7f 100644
--- a/net/sched/act_pedit.c
+++ b/net/sched/act_pedit.c
@@ -169,6 +169,7 @@ static int tcf_pedit(struct sk_buff *skb, const struct tc_action *a,
 			u32 *ptr, _data;
 			int offset = tkey->off;
 			int hoffset;
+			u32 val;
 			int rc;
 			enum pedit_header_type htype =
 				PEDIT_TYPE_GET(tkey->shift);
@@ -214,7 +215,20 @@ static int tcf_pedit(struct sk_buff *skb, const struct tc_action *a,
 			if (!ptr)
 				goto bad;
 			/* just do it, baby */
-			*ptr = ((*ptr & tkey->mask) ^ tkey->val);
+			switch (PEDIT_CMD_GET(tkey->shift)) {
+			case PEDIT_CMD_SET:
+				val = tkey->val;
+				break;
+			case PEDIT_CMD_ADD:
+				val = (*ptr + tkey->val) & ~tkey->mask;
+				break;
+			default:
+				pr_info("tc filter pedit bad command (%d)\n",
+					PEDIT_CMD_GET(tkey->shift));
+				goto bad;
+			}
+
+			*ptr = ((*ptr & tkey->mask) ^ val);
 			if (ptr == &_data)
 				skb_store_bits(skb, hoffset + offset, ptr, 4);
 		}
-- 
2.10.2