iplink_vxlan: Add DF configuration

Allow to set the DF bit behaviour for outgoing IPv4 packets: it can be
always on, inherited from the inner header, or, by default, always off,
which is the current behaviour.

v2:
- Indicate in the man page what DF refers to, using RFC 791 wording
  (David Ahern)

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: David Ahern <dsahern@gmail.com>

include/uapi/linux/if_link.h

@@ -531,6 +531,7 @@ enum {
 	IFLA_VXLAN_LABEL,
 	IFLA_VXLAN_GPE,
 	IFLA_VXLAN_TTL_INHERIT,
+	IFLA_VXLAN_DF,
 	__IFLA_VXLAN_MAX
 };
 #define IFLA_VXLAN_MAX	(__IFLA_VXLAN_MAX - 1)
@@ -540,6 +541,14 @@ struct ifla_vxlan_port_range {
 	__be16	high;
 };
 
+enum ifla_vxlan_df {
+	VXLAN_DF_UNSET = 0,
+	VXLAN_DF_SET,
+	VXLAN_DF_INHERIT,
+	__VXLAN_DF_END,
+	VXLAN_DF_MAX = __VXLAN_DF_END - 1,
+};
+
 /* GENEVE section */
 enum {
 	IFLA_GENEVE_UNSPEC,

ip/iplink_vxlan.c

@@ -31,6 +31,7 @@ static void print_explain(FILE *f)
 		"                 [ local ADDR ]\n"
 		"                 [ ttl TTL ]\n"
 		"                 [ tos TOS ]\n"
+		"                 [ df DF ]\n"
 		"                 [ flowlabel LABEL ]\n"
 		"                 [ dev PHYS_DEV ]\n"
 		"                 [ dstport PORT ]\n"
@@ -52,6 +53,7 @@ static void print_explain(FILE *f)
 		"       ADDR  := { IP_ADDRESS | any }\n"
 		"       TOS   := { NUMBER | inherit }\n"
 		"       TTL   := { 1..255 | auto | inherit }\n"
+		"       DF    := { unset | set | inherit }\n"
 		"       LABEL := 0-1048575\n"
 	);
 }
@@ -170,6 +172,22 @@ static int vxlan_parse_opt(struct link_util *lu, int argc, char **argv,
 			} else
 				tos = 1;
 			addattr8(n, 1024, IFLA_VXLAN_TOS, tos);
+		} else if (!matches(*argv, "df")) {
+			enum ifla_vxlan_df df;
+
+			NEXT_ARG();
+			check_duparg(&attrs, IFLA_VXLAN_DF, "df", *argv);
+			if (strcmp(*argv, "unset") == 0)
+				df = VXLAN_DF_UNSET;
+			else if (strcmp(*argv, "set") == 0)
+				df = VXLAN_DF_SET;
+			else if (strcmp(*argv, "inherit") == 0)
+				df = VXLAN_DF_INHERIT;
+			else
+				invarg("DF must be 'unset', 'set' or 'inherit'",
+				       *argv);
+
+			addattr8(n, 1024, IFLA_VXLAN_DF, df);
 		} else if (!matches(*argv, "label") ||
 			   !matches(*argv, "flowlabel")) {
 			__u32 uval;
@@ -538,6 +556,17 @@ static void vxlan_print_opt(struct link_util *lu, FILE *f, struct rtattr *tb[])
 			print_string(PRINT_FP, NULL, "ttl %s ", "auto");
 	}
 
+	if (tb[IFLA_VXLAN_DF]) {
+		enum ifla_vxlan_df df = rta_getattr_u8(tb[IFLA_VXLAN_DF]);
+
+		if (df == VXLAN_DF_UNSET)
+			print_string(PRINT_JSON, "df", "df %s ", "unset");
+		else if (df == VXLAN_DF_SET)
+			print_string(PRINT_ANY, "df", "df %s ", "set");
+		else if (df == VXLAN_DF_INHERIT)
+			print_string(PRINT_ANY, "df", "df %s ", "inherit");
+	}
+
 	if (tb[IFLA_VXLAN_LABEL]) {
 		__u32 label = rta_getattr_u32(tb[IFLA_VXLAN_LABEL]);
 

man/man8/ip-link.8.in

@@ -496,6 +496,8 @@ the following additional arguments are supported:
 ] [
 .BI tos " TOS "
 ] [
+.BI df " DF "
+] [
 .BI flowlabel " FLOWLABEL "
 ] [
 .BI dstport " PORT "
@@ -565,6 +567,18 @@ parameter.
 .BI tos " TOS"
 - specifies the TOS value to use in outgoing packets.
 
+.sp
+.BI df " DF"
+- specifies the usage of the Don't Fragment flag (DF) bit in outgoing packets
+with IPv4 headers. The value
+.B inherit
+causes the bit to be copied from the original IP header. The values
+.B unset
+and
+.B set
+cause the bit to be always unset or always set, respectively. By default, the
+bit is not set.
+
 .sp
 .BI flowlabel " FLOWLABEL"
 - specifies the flow label to use in outgoing packets.