Re: [PATCH v2 bpf-next 5/5] selftest: Add tests for XDP programs in devmap entries

On Thu, 28 May 2020 00:08:34 -0700
Andrii Nakryiko [off-list ref] wrote:

quoted

diff --git a/tools/testing/selftests/bpf/progs/test_xdp_with_devmap.c b/tools/testing/selftests/bpf/progs/test_xdp_with_devmap.c
new file mode 100644
index 000000000000..815cd59b4866
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_xdp_with_devmap.c

@@ -0,0 +1,17 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+struct bpf_map_def SEC("maps") dm_ports = {
+       .type = BPF_MAP_TYPE_DEVMAP,
+       .key_size = sizeof(__u32),
+       .value_size = sizeof(struct devmap_val),
+       .max_entries = 4,
+};
+  

This is an old syntax for maps, all the selftests were converted to
BTF-defined maps. Please update.

LOL - The map type BPF_MAP_TYPE_DEVMAP does not support BTF for key and
value, which it what I've been trying to point out... (and yes, I do
have code that makes it work in my tree.).

That said, you should use the new SEC(".maps") definitions, but you
need to use some tricks to avoid a BTF-ID getting generated.  Let me
help you with something that should work:

/* DEVMAP values */
struct devmap_val {
	__u32 ifindex;   /* device index */
};

struct {
	__uint(type, BPF_MAP_TYPE_DEVMAP);
	__uint(key_size, sizeof(u32));
	__uint(value_size, sizeof(struct devmap_val));
	__uint(max_entries, 4);
} dm_ports SEC(".maps");

Notice by setting key_size and value_size, instead of the "__type",
then a BTF-ID will be generated for this map.
Normally with proper BTF it should look like:

struct {
	__uint(type, BPF_MAP_TYPE_DEVMAP);
	__type(key, u32);
	__type(value, struct devmap_val);
	__uint(max_entries, 4);
} dm_ports_with_BTF SEC(".maps");


-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer