Subject: [PATCH iproute2] genl: print caps for all families

From: Jakub Kicinski <[email-masked]>
Date: Thu, 23 Feb 2023 17:52:34 -0800

Back in 2006 kernel commit 334c29a64507 ("[GENETLINK]: Move
command capabilities to flags.") removed some attributes and
moved the capabilities to flags. Corresponding iproute2
commit 26328fc3933f ("Add controller support for new features
exposed") added the ability to print those caps.

Printing is gated on version of the family, but we're checking
the version of each individual family rather than the control
family. The format of attributes in the control family
is dictated by the version of the control family alone.

Families can't use flags for random things, anyway,
because kernel core has a fixed interpretation.

Thanks to this change caps will be shown for all families
(assuming kernel newer than 2.6.19), not just those which
by coincidence have their local version >= 2.

For instance devlink, before:

  $ genl ctrl get name devlink
  Name: devlink
	ID: 0x15  Version: 0x1  header size: 0  max attribs: 179
	commands supported:
		#1:  ID-0x1
		#2:  ID-0x5
		#3:  ID-0x6
		...

after:

  $ genl ctrl get name devlink
  Name: devlink
	ID: 0x15  Version: 0x1  header size: 0  max attribs: 179
	commands supported:
		#1:  ID-0x1
		Capabilities (0xe):
 		  can doit; can dumpit; has policy

		#2:  ID-0x5
		Capabilities (0xe):
 		  can doit; can dumpit; has policy

		#3:  ID-0x6
		Capabilities (0xb):
 		  requires admin permission; can doit; has policy

Leave ctrl_v as 0 if we fail to read the version. Old code used 1
as the default, but 0 or 1 - does not matter, checks are for >= 2.

Signed-off-by: Jakub Kicinski <[email-masked]>
---
Not really sure if this is a fix or not..
---
 genl/ctrl.c | 56 +++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 54 insertions(+), 2 deletions(-)

diff --git a/genl/ctrl.c b/genl/ctrl.c
index a2d87af0ad07..1fcb3848f137 100644
--- a/genl/ctrl.c
+++ b/genl/ctrl.c
@@ -21,6 +21,8 @@
 #define GENL_MAX_FAM_OPS	256
 #define GENL_MAX_FAM_GRPS	256
 
+static unsigned int ctrl_v;
+
 static int usage(void)
 {
 	fprintf(stderr,"Usage: ctrl <CMD>\n" \
@@ -109,7 +111,6 @@ static int print_ctrl(struct rtnl_ctrl_data *ctrl,
 	int len = n->nlmsg_len;
 	struct rtattr *attrs;
 	FILE *fp = (FILE *) arg;
-	__u32 ctrl_v = 0x1;
 
 	if (n->nlmsg_type !=  GENL_ID_CTRL) {
 		fprintf(stderr, "Not a controller message, nlmsg_len=%d "
@@ -148,7 +149,6 @@ static int print_ctrl(struct rtnl_ctrl_data *ctrl,
 	if (tb[CTRL_ATTR_VERSION]) {
 		__u32 *v = RTA_DATA(tb[CTRL_ATTR_VERSION]);
 		fprintf(fp, " Version: 0x%x ",*v);
-		ctrl_v = *v;
 	}
 	if (tb[CTRL_ATTR_HDRSIZE]) {
 		__u32 *h = RTA_DATA(tb[CTRL_ATTR_HDRSIZE]);
@@ -241,6 +241,55 @@ static int print_ctrl2(struct nlmsghdr *n, void *arg)
 	return print_ctrl(NULL, n, arg);
 }
 
+static void ctrl_load_ctrl_version(struct rtnl_handle *rth)
+{
+	struct rtattr *tb[CTRL_ATTR_MAX + 1];
+	struct genlmsghdr *ghdr;
+	struct rtattr *attrs;
+	struct {
+		struct nlmsghdr         n;
+		struct genlmsghdr	g;
+		char                    buf[128];
+	} req = {
+		.n.nlmsg_len = NLMSG_LENGTH(GENL_HDRLEN),
+		.n.nlmsg_flags = NLM_F_REQUEST,
+		.n.nlmsg_type = GENL_ID_CTRL,
+		.g.cmd = CTRL_CMD_GETFAMILY,
+	};
+	struct nlmsghdr *nlh = &req.n;
+	struct nlmsghdr *answer = NULL;
+	__u16 id = GENL_ID_CTRL;
+	int len;
+
+	addattr_l(nlh, 128, CTRL_ATTR_FAMILY_ID, &id, 2);
+
+	if (rtnl_talk(rth, nlh, &answer) < 0) {
+		fprintf(stderr, "Error talking to the kernel\n");
+		return;
+	}
+
+	ghdr = NLMSG_DATA(answer);
+	if (answer->nlmsg_type != GENL_ID_CTRL ||
+	    ghdr->cmd != CTRL_CMD_NEWFAMILY) {
+		fprintf(stderr, "Unexpected reply nlmsg_type=%u cmd=%u\n",
+			answer->nlmsg_type, ghdr->cmd);
+		return;
+	}
+
+	len = answer->nlmsg_len;
+	len -= NLMSG_LENGTH(GENL_HDRLEN);
+	if (len < 0) {
+		fprintf(stderr, "wrong controller message len %d\n", len);
+		return;
+	}
+
+	attrs = (struct rtattr *) ((char *) ghdr + GENL_HDRLEN);
+	parse_rtattr_flags(tb, CTRL_ATTR_MAX, attrs, len, NLA_F_NESTED);
+
+	if (tb[CTRL_ATTR_VERSION])
+		ctrl_v = rta_getattr_u16(tb[CTRL_ATTR_VERSION]);
+}
+
 static int ctrl_list(int cmd, int argc, char **argv)
 {
 	struct rtnl_handle rth;
@@ -264,6 +313,9 @@ static int ctrl_list(int cmd, int argc, char **argv)
 		exit(1);
 	}
 
+	if (!ctrl_v)
+		ctrl_load_ctrl_version(&rth);
+
 	if (cmd == CTRL_CMD_GETFAMILY || cmd == CTRL_CMD_GETPOLICY) {
 		req.g.cmd = cmd;
 
-- 
2.39.2