netdev - [PATCH net-next 2/8] net/packet: constify packet_lookup_frame() and __tpacket_has

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Message-Id: <20190612165233.109749-3-edumazet@google.com>
Date:   Wed, 12 Jun 2019 09:52:27 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>,
        Willem de Bruijn <willemb@...gle.com>,
        Mahesh Bandewar <maheshb@...gle.com>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: [PATCH net-next 2/8] net/packet: constify packet_lookup_frame() and __tpacket_has_room()

Goal is to be able to use __tpacket_has_room() without holding a lock.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/packet/af_packet.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 66fcfd5b51f82a861795e002e91d3cbc69ab545a..273bffd2130d36cceb9947540a8511a51895874a 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -460,10 +460,10 @@ static __u32 __packet_set_timestamp(struct packet_sock *po, void *frame,
 	return ts_status;
 }
 
-static void *packet_lookup_frame(struct packet_sock *po,
-		struct packet_ring_buffer *rb,
-		unsigned int position,
-		int status)
+static void *packet_lookup_frame(const struct packet_sock *po,
+				 const struct packet_ring_buffer *rb,
+				 unsigned int position,
+				 int status)
 {
 	unsigned int pg_vec_pos, frame_offset;
 	union tpacket_uhdr h;
@@ -1198,12 +1198,12 @@ static void packet_free_pending(struct packet_sock *po)
 #define ROOM_LOW	0x1
 #define ROOM_NORMAL	0x2
 
-static bool __tpacket_has_room(struct packet_sock *po, int pow_off)
+static bool __tpacket_has_room(const struct packet_sock *po, int pow_off)
 {
 	int idx, len;
 
-	len = po->rx_ring.frame_max + 1;
-	idx = po->rx_ring.head;
+	len = READ_ONCE(po->rx_ring.frame_max) + 1;
+	idx = READ_ONCE(po->rx_ring.head);
 	if (pow_off)
 		idx += len >> pow_off;
 	if (idx >= len)
-- 
2.22.0.rc2.383.gf4fbbf30c2-goog