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>

include/net/dropreason.h

@@ -181,4 +181,6 @@ enum skb_drop_reason {
 			SKB_DR_SET(name, reason);		\
 	} while (0)
 
+extern const char * const drop_reasons[];
+
 #endif

include/trace/events/skb.h

@@ -9,92 +9,6 @@
 #include <linux/netdevice.h>
 #include <linux/tracepoint.h>
 
-#define TRACE_SKB_DROP_REASON					\
-	EM(SKB_DROP_REASON_NOT_SPECIFIED, NOT_SPECIFIED)	\
-	EM(SKB_DROP_REASON_NO_SOCKET, NO_SOCKET)		\
-	EM(SKB_DROP_REASON_PKT_TOO_SMALL, PKT_TOO_SMALL)	\
-	EM(SKB_DROP_REASON_TCP_CSUM, TCP_CSUM)			\
-	EM(SKB_DROP_REASON_SOCKET_FILTER, SOCKET_FILTER)	\
-	EM(SKB_DROP_REASON_UDP_CSUM, UDP_CSUM)			\
-	EM(SKB_DROP_REASON_NETFILTER_DROP, NETFILTER_DROP)	\
-	EM(SKB_DROP_REASON_OTHERHOST, OTHERHOST)		\
-	EM(SKB_DROP_REASON_IP_CSUM, IP_CSUM)			\
-	EM(SKB_DROP_REASON_IP_INHDR, IP_INHDR)			\
-	EM(SKB_DROP_REASON_IP_RPFILTER, IP_RPFILTER)		\
-	EM(SKB_DROP_REASON_UNICAST_IN_L2_MULTICAST,		\
-	   UNICAST_IN_L2_MULTICAST)				\
-	EM(SKB_DROP_REASON_XFRM_POLICY, XFRM_POLICY)		\
-	EM(SKB_DROP_REASON_IP_NOPROTO, IP_NOPROTO)		\
-	EM(SKB_DROP_REASON_SOCKET_RCVBUFF, SOCKET_RCVBUFF)	\
-	EM(SKB_DROP_REASON_PROTO_MEM, PROTO_MEM)		\
-	EM(SKB_DROP_REASON_TCP_MD5NOTFOUND, TCP_MD5NOTFOUND)	\
-	EM(SKB_DROP_REASON_TCP_MD5UNEXPECTED,			\
-	   TCP_MD5UNEXPECTED)					\
-	EM(SKB_DROP_REASON_TCP_MD5FAILURE, TCP_MD5FAILURE)	\
-	EM(SKB_DROP_REASON_SOCKET_BACKLOG, SOCKET_BACKLOG)	\
-	EM(SKB_DROP_REASON_TCP_FLAGS, TCP_FLAGS)		\
-	EM(SKB_DROP_REASON_TCP_ZEROWINDOW, TCP_ZEROWINDOW)	\
-	EM(SKB_DROP_REASON_TCP_OLD_DATA, TCP_OLD_DATA)		\
-	EM(SKB_DROP_REASON_TCP_OVERWINDOW, TCP_OVERWINDOW)	\
-	EM(SKB_DROP_REASON_TCP_OFOMERGE, TCP_OFOMERGE)		\
-	EM(SKB_DROP_REASON_TCP_OFO_DROP, TCP_OFO_DROP)		\
-	EM(SKB_DROP_REASON_TCP_RFC7323_PAWS, TCP_RFC7323_PAWS)	\
-	EM(SKB_DROP_REASON_TCP_INVALID_SEQUENCE,		\
-	   TCP_INVALID_SEQUENCE)				\
-	EM(SKB_DROP_REASON_TCP_RESET, TCP_RESET)		\
-	EM(SKB_DROP_REASON_TCP_INVALID_SYN, TCP_INVALID_SYN)	\
-	EM(SKB_DROP_REASON_TCP_CLOSE, TCP_CLOSE)		\
-	EM(SKB_DROP_REASON_TCP_FASTOPEN, TCP_FASTOPEN)		\
-	EM(SKB_DROP_REASON_TCP_OLD_ACK, TCP_OLD_ACK)		\
-	EM(SKB_DROP_REASON_TCP_TOO_OLD_ACK, TCP_TOO_OLD_ACK)	\
-	EM(SKB_DROP_REASON_TCP_ACK_UNSENT_DATA,			\
-	   TCP_ACK_UNSENT_DATA)					\
-	EM(SKB_DROP_REASON_TCP_OFO_QUEUE_PRUNE,			\
-	  TCP_OFO_QUEUE_PRUNE)					\
-	EM(SKB_DROP_REASON_IP_OUTNOROUTES, IP_OUTNOROUTES)	\
-	EM(SKB_DROP_REASON_BPF_CGROUP_EGRESS,			\
-	   BPF_CGROUP_EGRESS)					\
-	EM(SKB_DROP_REASON_IPV6DISABLED, IPV6DISABLED)		\
-	EM(SKB_DROP_REASON_NEIGH_CREATEFAIL, NEIGH_CREATEFAIL)	\
-	EM(SKB_DROP_REASON_NEIGH_FAILED, NEIGH_FAILED)		\
-	EM(SKB_DROP_REASON_NEIGH_QUEUEFULL, NEIGH_QUEUEFULL)	\
-	EM(SKB_DROP_REASON_NEIGH_DEAD, NEIGH_DEAD)		\
-	EM(SKB_DROP_REASON_TC_EGRESS, TC_EGRESS)		\
-	EM(SKB_DROP_REASON_QDISC_DROP, QDISC_DROP)		\
-	EM(SKB_DROP_REASON_CPU_BACKLOG, CPU_BACKLOG)		\
-	EM(SKB_DROP_REASON_XDP, XDP)				\
-	EM(SKB_DROP_REASON_TC_INGRESS, TC_INGRESS)		\
-	EM(SKB_DROP_REASON_UNHANDLED_PROTO, UNHANDLED_PROTO)	\
-	EM(SKB_DROP_REASON_SKB_CSUM, SKB_CSUM)			\
-	EM(SKB_DROP_REASON_SKB_GSO_SEG, SKB_GSO_SEG)		\
-	EM(SKB_DROP_REASON_SKB_UCOPY_FAULT, SKB_UCOPY_FAULT)	\
-	EM(SKB_DROP_REASON_DEV_HDR, DEV_HDR)			\
-	EM(SKB_DROP_REASON_DEV_READY, DEV_READY)		\
-	EM(SKB_DROP_REASON_FULL_RING, FULL_RING)		\
-	EM(SKB_DROP_REASON_NOMEM, NOMEM)			\
-	EM(SKB_DROP_REASON_HDR_TRUNC, HDR_TRUNC)		\
-	EM(SKB_DROP_REASON_TAP_FILTER, TAP_FILTER)		\
-	EM(SKB_DROP_REASON_TAP_TXFILTER, TAP_TXFILTER)		\
-	EM(SKB_DROP_REASON_ICMP_CSUM, ICMP_CSUM)		\
-	EM(SKB_DROP_REASON_INVALID_PROTO, INVALID_PROTO)	\
-	EM(SKB_DROP_REASON_IP_INADDRERRORS, IP_INADDRERRORS)	\
-	EM(SKB_DROP_REASON_IP_INNOROUTES, IP_INNOROUTES)	\
-	EM(SKB_DROP_REASON_PKT_TOO_BIG, PKT_TOO_BIG)		\
-	EMe(SKB_DROP_REASON_MAX, MAX)
-
-#undef EM
-#undef EMe
-
-#define EM(a, b)	TRACE_DEFINE_ENUM(a);
-#define EMe(a, b)	TRACE_DEFINE_ENUM(a);
-
-TRACE_SKB_DROP_REASON
-
-#undef EM
-#undef EMe
-#define EM(a, b)	{ a, #b },
-#define EMe(a, b)	{ a, #b }
-
 /*
  * Tracepoint for free an sk_buff:
  */
@@ -121,8 +35,7 @@ TRACE_EVENT(kfree_skb,
 
 	TP_printk("skbaddr=%p protocol=%u location=%p reason: %s",
 		  __entry->skbaddr, __entry->protocol, __entry->location,
-		  __print_symbolic(__entry->reason,
-				   TRACE_SKB_DROP_REASON))
+		  drop_reasons[__entry->reason])
 );
 
 TRACE_EVENT(consume_skb,

net/core/.gitignore

+dropreason_str.c

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

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.

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