[PATCH 4/6] socketutils: build a xlat table dynamically for decoding "family" field of Netlink GENERIC protocol

[Masatake YAMATO]

* socketutils.c (genl_families_xlat): exported function for building
the xlat table. Include linux/genetlink.h.

* defs.h (genl_families_xlat): add the declaration.
(genl_send_dump_families, genl_parse_families_response):
helper functions.

Signed-off-by: Masatake YAMATO <yamato at redhat.com>
---
 defs.h        |  3 ++
 socketutils.c | 98 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 101 insertions(+)

diff --git a/defs.h b/defs.h
index b9bdbb2..17a2a95 100644
--- a/defs.h
+++ b/defs.h
@@ -1025,4 +1025,7 @@ struct dyxlat *dyxlat_new    (int allocation);
 void dyxlat_delete (struct dyxlat *dyxlat);
 struct xlat *dyxlat_get (struct dyxlat *dyxlat);
 void dyxlat_may_add_pair (struct dyxlat *dyxlat, uint64_t val, const char *str);
+
+struct xlat *genl_families_xlat(void);
+
 #endif /* !STRACE_DEFS_H */
diff --git a/socketutils.c b/socketutils.c
index 0016942..4fc1d67 100644
--- a/socketutils.c
+++ b/socketutils.c
@@ -37,6 +37,7 @@
 #include <linux/unix_diag.h>
 #include <linux/netlink_diag.h>
 #include <linux/rtnetlink.h>
+#include <linux/genetlink.h>
 
 #include <sys/un.h>
 #ifndef UNIX_PATH_MAX
@@ -541,3 +542,100 @@ print_sockaddr_by_inode(struct tcb *const tcp, const int fd,
 	return print_sockaddr_by_inode_cached(inode) ? true :
 		print_sockaddr_by_inode_uncached(inode, getfdproto(tcp, fd));
 }
+
+/*
+ * Managing the cache for decoding communications of Netlink GENERIC protocol
+ *
+ * As name shown Netlink GENERIC protocol is generic protocol. The
+ * numbers of msg types used in the protocol are not defined
+ * statically. Kernel defines them on demand.  So the xlat converted
+ * from header files doesn't help for decoding the protocol. Following
+ * codes are building xlat(dyxlat) at runtime.
+ */
+static bool
+genl_send_dump_families(const int fd)
+{
+	struct {
+		const struct nlmsghdr nlh;
+		struct genlmsghdr gnlh;
+	} req = {
+		.nlh = {
+			.nlmsg_len = sizeof(req),
+			.nlmsg_type = GENL_ID_CTRL,
+			.nlmsg_flags = NLM_F_DUMP|NLM_F_REQUEST|NLM_F_ACK,
+		},
+		.gnlh = {
+			.cmd = CTRL_CMD_GETFAMILY,
+		}
+	};
+	return send_query(fd, &req, sizeof(req));
+}
+
+static int
+genl_parse_families_response(const void *const data,
+			     const int data_len, const unsigned long inode,
+			     void *user_data)
+{
+	struct dyxlat *dyxlat = user_data;
+	const struct genlmsghdr * const gnlh = data;
+	struct rtattr *attr;
+	int rta_len = data_len - NLMSG_LENGTH(sizeof(*gnlh));
+
+	char *name = NULL;
+	uint16_t id = 0;
+	bool id_set = false;
+
+	if (rta_len < 0)
+		return -1;
+	if (gnlh->cmd != CTRL_CMD_NEWFAMILY)
+		return -1;
+	if (gnlh->version != 2)
+		return -1;
+
+	for (attr = (struct rtattr *) (gnlh + 1);
+	     RTA_OK(attr, rta_len);
+	     attr = RTA_NEXT(attr, rta_len)) {
+		switch (attr->rta_type) {
+		case CTRL_ATTR_FAMILY_NAME:
+			name = xstrdup(RTA_DATA(attr));
+			break;
+		case CTRL_ATTR_FAMILY_ID:
+			if (RTA_PAYLOAD(attr) >= 2) {
+				id = *(uint16_t *)(RTA_DATA(attr));
+				id_set = true;
+			}
+			break;
+		}
+		if (name && id_set) {
+			dyxlat_may_add_pair (dyxlat, id, name);
+			id_set = false;
+			free (name);
+			name = NULL;
+		}
+	}
+	return 0;
+}
+
+struct xlat *
+genl_families_xlat(void)
+{
+	static struct dyxlat *dyxlat;
+
+	if (!dyxlat) {
+		int fd;
+
+		dyxlat = dyxlat_new(32);
+
+		fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_GENERIC);
+		if (fd < 0)
+			goto out;
+
+		if (genl_send_dump_families(fd))
+			receive_responses(fd, 0, GENL_ID_CTRL, dyxlat,
+					  genl_parse_families_response);
+		close(fd);
+	}
+
+  out:
+	return dyxlat_get(dyxlat);
+}
-- 
2.9.4