[PATCHv2 iproute2-next] ip/geneve: fix ttl inherit behavior

[Hangbin Liu <liuhangbin@gmail.com>]

Currently when we add geneve with "ttl inherit", we only set ttl to 0, which
is actually use whatever default value instead of inherit the inner protocol's
ttl value.

To make a difference with ttl inherit and ttl == 0, we add an attribute
IFLA_GENEVE_TTL_INHERIT in kernel commit 52d0d404d39dd ("geneve: add ttl
inherit support"). Now let's use "ttl inherit" to inherit the inner
protocol's ttl, and use "ttl auto" to means "use whatever default value",
the same behavior with ttl == 0.

v2:
1) remove IFLA_GENEVE_TTL_INHERIT defination in if_link.h as it's already
   updated.
2) Still use addattr8() so we can enable/disable ttl inherit, as Michal
   suggested.

Reported-by: Jianlin Shi <jishi@redhat.com>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
---
 ip/iplink_geneve.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/ip/iplink_geneve.c b/ip/iplink_geneve.c
index 26e70ff..c417842 100644
--- a/ip/iplink_geneve.c
+++ b/ip/iplink_geneve.c
@@ -34,7 +34,7 @@ static void print_explain(FILE *f)
 		"Where: VNI   := 0-16777215\n"
 		"       ADDR  := IP_ADDRESS\n"
 		"       TOS   := { NUMBER | inherit }\n"
-		"       TTL   := { 1..255 | inherit }\n"
+		"       TTL   := { 1..255 | auto | inherit }\n"
 		"       LABEL := 0-1048575\n"
 	);
 }
@@ -94,7 +94,9 @@ static int geneve_parse_opt(struct link_util *lu, int argc, char **argv,
 
 			NEXT_ARG();
 			check_duparg(&attrs, IFLA_GENEVE_TTL, "ttl", *argv);
-			if (strcmp(*argv, "inherit") != 0) {
+			if (strcmp(*argv, "inherit") == 0) {
+				addattr8(n, 1024, IFLA_GENEVE_TTL_INHERIT, 1);
+			} else if (strcmp(*argv, "auto") != 0) {
 				if (get_unsigned(&uval, *argv, 0))
 					invarg("invalid TTL", *argv);
 				if (uval > 255)
@@ -265,12 +267,16 @@ static void geneve_print_opt(struct link_util *lu, FILE *f, struct rtattr *tb[])
 		}
 	}
 
-	if (tb[IFLA_GENEVE_TTL])
-		ttl = rta_getattr_u8(tb[IFLA_GENEVE_TTL]);
-	if (is_json_context() || ttl)
-		print_uint(PRINT_ANY, "ttl", "ttl %u ", ttl);
-	else
+	if (tb[IFLA_GENEVE_TTL_INHERIT] &&
+	    rta_getattr_u8(tb[IFLA_GENEVE_TTL_INHERIT])) {
 		print_string(PRINT_FP, NULL, "ttl %s ", "inherit");
+	} else if (tb[IFLA_GENEVE_TTL]) {
+		ttl = rta_getattr_u8(tb[IFLA_GENEVE_TTL]);
+		if (is_json_context() || ttl)
+			print_uint(PRINT_ANY, "ttl", "ttl %u ", ttl);
+		else
+			print_string(PRINT_FP, NULL, "ttl %s ", "auto");
+	}
 
 	if (tb[IFLA_GENEVE_TOS])
 		tos = rta_getattr_u8(tb[IFLA_GENEVE_TOS]);
-- 
2.5.5