[PATCH bpf V8 1/7] selftests/bpf: xdp_hw_metadata default disable bpf_printk

[Jesper Dangaard Brouer]

The tool xdp_hw_metadata can be used by driver developers
implementing XDP-hints kfuncs.  The tool transfers the
XDP-hints via metadata information to an AF_XDP userspace
process. When everything works the bpf_printk calls are
unncesssary.  Thus, disable bpf_printk by default, but
make it easy to reenable for driver developers to use
when debugging their driver implementation.

Next patch will add counters to track some of these cases.
That will provide a hint to re-enable bpf_printk.

This also converts bpf_printk "forwarding UDP:9091 to AF_XDP"
into a code comment.  The bpf_printk's that are important
to the driver developers is when bpf_xdp_adjust_meta fails.
The likely mistake from driver developers is expected to
be that they didn't implement XDP metadata adjust support.

Signed-off-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
---
 .../testing/selftests/bpf/progs/xdp_hw_metadata.c  |   16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c b/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c
index 4c55b4d79d3d..b0104763405a 100644
--- a/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c
+++ b/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c
@@ -5,6 +5,19 @@
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_endian.h>
 
+/* Per default below bpf_printk() calls are disabled.  Can be
+ * reenabled manually for convenience by XDP-hints driver developer,
+ * when troubleshooting the drivers kfuncs implementation details.
+ *
+ * Remember BPF-prog bpf_printk info output can be access via:
+ *  /sys/kernel/debug/tracing/trace_pipe
+ */
+//#define DEBUG	1
+#ifndef DEBUG
+#undef  bpf_printk
+#define bpf_printk(fmt, ...) ({})
+#endif
+
 struct {
 	__uint(type, BPF_MAP_TYPE_XSKMAP);
 	__uint(max_entries, 256);
@@ -49,11 +62,10 @@ int rx(struct xdp_md *ctx)
 	if (!udp)
 		return XDP_PASS;
 
+	/* Forwarding UDP:9091 to AF_XDP */
 	if (udp->dest != bpf_htons(9091))
 		return XDP_PASS;
 
-	bpf_printk("forwarding UDP:9091 to AF_XDP");
-
 	ret = bpf_xdp_adjust_meta(ctx, -(int)sizeof(struct xdp_meta));
 	if (ret != 0) {
 		bpf_printk("bpf_xdp_adjust_meta returned %d", ret);