[PATCH net-next] samples/bpf: Fix map interation in xdp1_user

[PATCH net-next] samples/bpf: Fix map interation in xdp1_user

[Gerhard Engleder]

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@engleder-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

Re: [PATCH net-next] samples/bpf: Fix map interation in xdp1_user

[Song Liu]

On Thu, Oct 13, 2022 at 2:01 PM Gerhard Engleder
<gerhard@engleder-embedded.com> wrote:
>
> 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@engleder-embedded.com>

Acked-by: Song Liu <song@kernel.org>

> ---
>  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
>

Re: [PATCH net-next] samples/bpf: Fix map interation in xdp1_user

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Martin KaFai Lau <martin.lau@kernel.org>:

On Thu, 13 Oct 2022 22:09:22 +0200 you wrote:
> 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.
> 
> [...]

Here is the summary with links:
  - [net-next] samples/bpf: Fix map interation in xdp1_user
    https://git.kernel.org/bpf/bpf-next/c/05ee658c654b

You are awesome, thank you!
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