net: skb: use auto-generation to convert skb drop reason to string

It is annoying to add new skb drop reasons to 'enum skb_drop_reason'
and TRACE_SKB_DROP_REASON in trace/event/skb.h, and it's easy to forget
to add the new reasons we added to TRACE_SKB_DROP_REASON.

TRACE_SKB_DROP_REASON is used to convert drop reason of type number
to string. For now, the string we passed to user space is exactly the
same as the name in 'enum skb_drop_reason' with a 'SKB_DROP_REASON_'
prefix. Therefore, we can use 'auto-generation' to generate these
drop reasons to string at build time.

The new source 'dropreason_str.c' will be auto generated during build
time, which contains the string array
'const char * const drop_reasons[]'.

Signed-off-by: Menglong Dong <imagedong@tencent.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

4 files changed, 26 insertions, 14 deletions

diff --git a/net/core/.gitignore b/net/core/.gitignore
new file mode 100644
index 000000000000..df1e74372cce
--- /dev/null
+++ b/net/core/.gitignore
@@ -0,0 +1 @@
+dropreason_str.c
diff --git a/net/core/Makefile b/net/core/Makefile
index a8e4f737692b..e8ce3bd283a6 100644
--- a/net/core/Makefile
+++ b/net/core/Makefile
@@ -4,7 +4,8 @@
 #
 
 obj-y := sock.o request_sock.o skbuff.o datagram.o stream.o scm.o \
-	 gen_stats.o gen_estimator.o net_namespace.o secure_seq.o flow_dissector.o
+	 gen_stats.o gen_estimator.o net_namespace.o secure_seq.o \
+	 flow_dissector.o dropreason_str.o
 
 obj-$(CONFIG_SYSCTL) += sysctl_net_core.o
 
@@ -39,3 +40,23 @@ obj-$(CONFIG_NET_SOCK_MSG) += skmsg.o
 obj-$(CONFIG_BPF_SYSCALL) += sock_map.o
 obj-$(CONFIG_BPF_SYSCALL) += bpf_sk_storage.o
 obj-$(CONFIG_OF)	+= of_net.o
+
+clean-files := dropreason_str.c
+
+quiet_cmd_dropreason_str = GEN     $@
+cmd_dropreason_str = awk -F ',' 'BEGIN{ print "\#include <net/dropreason.h>\n"; \
+	print "const char * const drop_reasons[] = {" }\
+	/^enum skb_drop/ { dr=1; }\
+	/^\};/ { dr=0; }\
+	/^\tSKB_DROP_REASON_/ {\
+		if (dr) {\
+			sub(/\tSKB_DROP_REASON_/, "", $$1);\
+			printf "\t[SKB_DROP_REASON_%s] = \"%s\",\n", $$1, $$1;\
+		}\
+	}\
+	END{ print "};" }' $< > $@
+
+$(obj)/dropreason_str.c: $(srctree)/include/net/dropreason.h
+	$(call cmd,dropreason_str)
+
+$(obj)/dropreason_str.o: $(obj)/dropreason_str.c
diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c
index 41cac0e4834e..4ad1decce724 100644
--- a/net/core/drop_monitor.c
+++ b/net/core/drop_monitor.c
@@ -48,19 +48,6 @@
 static int trace_state = TRACE_OFF;
 static bool monitor_hw;
 
-#undef EM
-#undef EMe
-
-#define EM(a, b)	[a] = #b,
-#define EMe(a, b)	[a] = #b
-
-/* drop_reasons is used to translate 'enum skb_drop_reason' to string,
- * which is reported to user space.
- */
-static const char * const drop_reasons[] = {
-	TRACE_SKB_DROP_REASON
-};
-
 /* net_dm_mutex
  *
  * An overall lock guarding every operation coming from userspace.
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 5b3559cb1d82..b661040c100e 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -91,6 +91,9 @@ static struct kmem_cache *skbuff_ext_cache __ro_after_init;
 int sysctl_max_skb_frags __read_mostly = MAX_SKB_FRAGS;
 EXPORT_SYMBOL(sysctl_max_skb_frags);
 
+/* The array 'drop_reasons' is auto-generated in dropreason_str.c */
+EXPORT_SYMBOL(drop_reasons);
+
 /**
  *	skb_panic - private function for out-of-line support
  *	@skb:	buffer