[NETLINK]: Generic netlink family

The generic netlink family builds on top of netlink and provides
simplifies access for the less demanding netlink users. It solves
the problem of protocol numbers running out by introducing a so
called controller taking care of id management and name resolving.

Generic netlink modules register themself after filling out their
id card (struct genl_family), after successful registration the
modules are able to register callbacks to command numbers by
filling out a struct genl_ops and calling genl_register_op(). The
registered callbacks are invoked with attributes parsed making
life of simple modules a lot easier.

Although generic netlink modules can request static identifiers,
it is recommended to use GENL_ID_GENERATE and to let the controller
assign a unique identifier to the module. Userspace applications
will then ask the controller and lookup the idenfier by the module
name.

Due to the current multicast implementation of netlink, the number
of generic netlink modules is restricted to 1024 to avoid wasting
memory for the per socket multiacst subscription bitmask.

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 205 insertions, 0 deletions

diff --git a/include/linux/genetlink.h b/include/linux/genetlink.h
new file mode 100644
index 000000000000..84f12a41dc01
--- /dev/null
+++ b/include/linux/genetlink.h
@@ -0,0 +1,51 @@
+#ifndef __LINUX_GENERIC_NETLINK_H
+#define __LINUX_GENERIC_NETLINK_H
+
+#include <linux/netlink.h>
+
+#define GENL_NAMSIZ     16      /* length of family name */
+
+#define GENL_MIN_ID     NLMSG_MIN_TYPE
+#define GENL_MAX_ID     1023
+
+struct genlmsghdr {
+        __u8    cmd;
+        __u8    version;
+        __u16   reserved;
+};
+
+#define GENL_HDRLEN     NLMSG_ALIGN(sizeof(struct genlmsghdr))
+
+/*
+ * List of reserved static generic netlink identifiers:
+ */
+#define GENL_ID_GENERATE        0
+#define GENL_ID_CTRL            NLMSG_MIN_TYPE
+
+/**************************************************************************
+ * Controller
+ **************************************************************************/
+
+enum {
+        CTRL_CMD_UNSPEC,
+        CTRL_CMD_NEWFAMILY,
+        CTRL_CMD_DELFAMILY,
+        CTRL_CMD_GETFAMILY,
+        CTRL_CMD_NEWOPS,
+        CTRL_CMD_DELOPS,
+        CTRL_CMD_GETOPS,
+        __CTRL_CMD_MAX,
+};
+
+#define CTRL_CMD_MAX (__CTRL_CMD_MAX - 1)
+
+enum {
+        CTRL_ATTR_UNSPEC,
+        CTRL_ATTR_FAMILY_ID,
+        CTRL_ATTR_FAMILY_NAME,
+        __CTRL_ATTR_MAX,
+};
+
+#define CTRL_ATTR_MAX (__CTRL_ATTR_MAX - 1)
+
+#endif  /* __LINUX_GENERIC_NETLINK_H */
diff --git a/include/net/genetlink.h b/include/net/genetlink.h
new file mode 100644
index 000000000000..52d8b1a73d52
--- /dev/null
+++ b/include/net/genetlink.h
@@ -0,0 +1,154 @@
+#ifndef __NET_GENERIC_NETLINK_H
+#define __NET_GENERIC_NETLINK_H
+
+#include <linux/genetlink.h>
+#include <net/netlink.h>
+
+/**
+ * struct genl_family - generic netlink family
+ * @id: protocol family idenfitier
+ * @hdrsize: length of user specific header in bytes
+ * @name: name of family
+ * @version: protocol version
+ * @maxattr: maximum number of attributes supported
+ * @attrbuf: buffer to store parsed attributes
+ * @ops_list: list of all assigned operations
+ * @family_list: family list
+ */
+struct genl_family
+{
+        unsigned int            id;
+        unsigned int            hdrsize;
+        char                    name[GENL_NAMSIZ];
+        unsigned int            version;
+        unsigned int            maxattr;
+        struct module *         owner;
+        struct nlattr **        attrbuf;        /* private */
+        struct list_head        ops_list;       /* private */
+        struct list_head        family_list;    /* private */
+};
+
+#define GENL_ADMIN_PERM         0x01
+
+/**
+ * struct genl_info - receiving information
+ * @snd_seq: sending sequence number
+ * @snd_pid: netlink pid of sender
+ * @nlhdr: netlink message header
+ * @genlhdr: generic netlink message header
+ * @userhdr: user specific header
+ * @attrs: netlink attributes
+ */
+struct genl_info
+{
+        u32                     snd_seq;
+        u32                     snd_pid;
+        struct nlmsghdr *       nlhdr;
+        struct genlmsghdr *     genlhdr;
+        void *                  userhdr;
+        struct nlattr **        attrs;
+};
+
+/**
+ * struct genl_ops - generic netlink operations
+ * @cmd: command identifier
+ * @flags: flags
+ * @policy: attribute validation policy
+ * @doit: standard command callback
+ * @dumpit: callback for dumpers
+ * @ops_list: operations list
+ */
+struct genl_ops
+{
+        unsigned int            cmd;
+        unsigned int            flags;
+        struct nla_policy       *policy;
+        int                    (*doit)(struct sk_buff *skb,
+                                       struct genl_info *info);
+        int                    (*dumpit)(struct sk_buff *skb,
+                                         struct netlink_callback *cb);
+        struct list_head        ops_list;
+};
+
+extern int genl_register_family(struct genl_family *family);
+extern int genl_unregister_family(struct genl_family *family);
+extern int genl_register_ops(struct genl_family *, struct genl_ops *ops);
+extern int genl_unregister_ops(struct genl_family *, struct genl_ops *ops);
+
+extern struct sock *genl_sock;
+
+/**
+ * genlmsg_put - Add generic netlink header to netlink message
+ * @skb: socket buffer holding the message
+ * @pid: netlink pid the message is addressed to
+ * @seq: sequence number (usually the one of the sender)
+ * @type: netlink message type
+ * @hdrlen: length of the user specific header
+ * @flags netlink message flags
+ * @cmd: generic netlink command
+ * @version: version
+ *
+ * Returns pointer to user specific header
+ */
+static inline void *genlmsg_put(struct sk_buff *skb, u32 pid, u32 seq,
+                                int type, int hdrlen, int flags,
+                                u8 cmd, u8 version)
+{
+        struct nlmsghdr *nlh;
+        struct genlmsghdr *hdr;
+
+        nlh = nlmsg_put(skb, pid, seq, type, GENL_HDRLEN + hdrlen, flags);
+        if (nlh == NULL)
+                return NULL;
+
+        hdr = nlmsg_data(nlh);
+        hdr->cmd = cmd;
+        hdr->version = version;
+        hdr->reserved = 0;
+
+        return (char *) hdr + GENL_HDRLEN;
+}
+
+/**
+ * genlmsg_end - Finalize a generic netlink message
+ * @skb: socket buffer the message is stored in
+ * @hdr: user specific header
+ */
+static inline int genlmsg_end(struct sk_buff *skb, void *hdr)
+{
+        return nlmsg_end(skb, hdr - GENL_HDRLEN - NLMSG_HDRLEN);
+}
+
+/**
+ * genlmsg_cancel - Cancel construction of a generic netlink message
+ * @skb: socket buffer the message is stored in
+ * @hdr: generic netlink message header
+ */
+static inline int genlmsg_cancel(struct sk_buff *skb, void *hdr)
+{
+        return nlmsg_cancel(skb, hdr - GENL_HDRLEN - NLMSG_HDRLEN);
+}
+
+/**
+ * genlmsg_multicast - multicast a netlink message
+ * @skb: netlink message as socket buffer
+ * @pid: own netlink pid to avoid sending to yourself
+ * @group: multicast group id
+ */
+static inline int genlmsg_multicast(struct sk_buff *skb, u32 pid,
+                                    unsigned int group)
+{
+        return nlmsg_multicast(genl_sock, skb, pid, group);
+}
+
+/**
+ * genlmsg_unicast - unicast a netlink message
+ * @skb: netlink message as socket buffer
+ * @pid: netlink pid of the destination socket
+ */
+static inline int genlmsg_unicast(struct sk_buff *skb, u32 pid)
+{
+        return nlmsg_unicast(genl_sock, skb, pid);
+}
+
+#endif  /* __NET_GENERIC_NETLINK_H */