netdev - [PATCH net-next] samples/bpf: Fix map interation in xdp1

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Message-Id: <20221013200922.17167-1-gerhard@engleder-embedded.com>
Date:   Thu, 13 Oct 2022 22:09:22 +0200
From:   Gerhard Engleder <gerhard@...leder-embedded.com>
To:     ast@...nel.org, daniel@...earbox.net, davem@...emloft.net,
        kuba@...nel.org, hawk@...nel.org, john.fastabend@...il.com
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        Gerhard Engleder <gerhard@...leder-embedded.com>
Subject: [PATCH net-next] samples/bpf: Fix map interation in xdp1_user

BPF map iteration in xdp1_user results in endless loop without any
output, because the return value of bpf_map_get_next_key() is checked
against the wrong value.

Other call locations of bpf_map_get_next_key() check for equal 0 for
continuing the iteration. xdp1_user checks against unequal -1. This is
wrong for a function which can return arbitrary negative errno values,
because a return value of e.g. -2 results in an endless loop.

With this fix xdp1_user is printing statistics again:
proto 0:          1 pkt/s
proto 0:          1 pkt/s
proto 17:     107383 pkt/s
proto 17:     881655 pkt/s
proto 17:     882083 pkt/s
proto 17:     881758 pkt/s

Signed-off-by: Gerhard Engleder <gerhard@...leder-embedded.com>
---
 samples/bpf/xdp1_user.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/samples/bpf/xdp1_user.c b/samples/bpf/xdp1_user.c
index ac370e638fa3..281dc964de8d 100644
--- a/samples/bpf/xdp1_user.c
+++ b/samples/bpf/xdp1_user.c
@@ -51,7 +51,7 @@ static void poll_stats(int map_fd, int interval)
 
 		sleep(interval);
 
-		while (bpf_map_get_next_key(map_fd, &key, &key) != -1) {
+		while (bpf_map_get_next_key(map_fd, &key, &key) == 0) {
 			__u64 sum = 0;
 
 			assert(bpf_map_lookup_elem(map_fd, &key, values) == 0);
-- 
2.30.2