[PATCH iproute2-next] geneve: fix ttl inherit behavior

[Hangbin Liu]

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

To respect compatibility with old behavior and make a difference between
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.

Reported-by: Jianlin Shi <ji...@redhat.com>
Signed-off-by: Hangbin Liu <liuhang...@gmail.com>
---
 include/uapi/linux/if_link.h |  1 +
 ip/iplink_geneve.c           | 20 +++++++++++++-------
 2 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/include/uapi/linux/if_link.h b/include/uapi/linux/if_link.h
index f4a9715..02d7bdf 100644
--- a/include/uapi/linux/if_link.h
+++ b/include/uapi/linux/if_link.h
@@ -552,6 +552,7 @@ enum {
        IFLA_GENEVE_UDP_ZERO_CSUM6_TX,
        IFLA_GENEVE_UDP_ZERO_CSUM6_RX,
        IFLA_GENEVE_LABEL,
+       IFLA_GENEVE_TTL_INHERIT,
        __IFLA_GENEVE_MAX
 };
 #define IFLA_GENEVE_MAX        (__IFLA_GENEVE_MAX - 1)
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