[PATCH bpf V7 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.

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..980eb60d8e5b 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 troublshooting 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);