[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, 580 insertions, 1 deletions

diff --git a/net/netlink/Makefile b/net/netlink/Makefile
index 6817901..e3589c2 100644
--- a/net/netlink/Makefile
+++ b/net/netlink/Makefile
@@ -2,4 +2,4 @@
 # Makefile for the netlink driver.
 #
 
-obj-y  				:= af_netlink.o attr.o
+obj-y  				:= af_netlink.o attr.o genetlink.o
diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
new file mode 100644
index 0000000..287cfcc
--- /dev/null
+++ b/net/netlink/genetlink.c
@@ -0,0 +1,579 @@
+/*
+ * NETLINK      Generic Netlink Family
+ *
+ * 		Authors:	Jamal Hadi Salim
+ * 				Thomas Graf <tgraf@suug.ch>
+ */
+
+#include <linux/config.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/types.h>
+#include <linux/socket.h>
+#include <linux/string.h>
+#include <linux/skbuff.h>
+#include <net/sock.h>
+#include <net/genetlink.h>
+
+struct sock *genl_sock = NULL;
+
+static DECLARE_MUTEX(genl_sem); /* serialization of message processing */
+
+static void genl_lock(void)
+{
+	down(&genl_sem);
+}
+
+static int genl_trylock(void)
+{
+	return down_trylock(&genl_sem);
+}
+
+static void genl_unlock(void)
+{
+	up(&genl_sem);
+
+	if (genl_sock && genl_sock->sk_receive_queue.qlen)
+		genl_sock->sk_data_ready(genl_sock, 0);
+}
+
+#define GENL_FAM_TAB_SIZE	16
+#define GENL_FAM_TAB_MASK	(GENL_FAM_TAB_SIZE - 1)
+
+static struct list_head family_ht[GENL_FAM_TAB_SIZE];
+
+static int genl_ctrl_event(int event, void *data);
+
+static inline unsigned int genl_family_hash(unsigned int id)
+{
+	return id & GENL_FAM_TAB_MASK;
+}
+
+static inline struct list_head *genl_family_chain(unsigned int id)
+{
+	return &family_ht[genl_family_hash(id)];
+}
+
+static struct genl_family *genl_family_find_byid(unsigned int id)
+{
+	struct genl_family *f;
+
+	list_for_each_entry(f, genl_family_chain(id), family_list)
+		if (f->id == id)
+			return f;
+
+	return NULL;
+}
+
+static struct genl_family *genl_family_find_byname(char *name)
+{
+	struct genl_family *f;
+	int i;
+
+	for (i = 0; i < GENL_FAM_TAB_SIZE; i++)
+		list_for_each_entry(f, genl_family_chain(i), family_list)
+			if (strcmp(f->name, name) == 0)
+				return f;
+
+	return NULL;
+}
+
+static struct genl_ops *genl_get_cmd(u8 cmd, struct genl_family *family)
+{
+	struct genl_ops *ops;
+
+	list_for_each_entry(ops, &family->ops_list, ops_list)
+		if (ops->cmd == cmd)
+			return ops;
+
+	return NULL;
+}
+
+/* Of course we are going to have problems once we hit
+ * 2^16 alive types, but that can only happen by year 2K
+*/
+static inline u16 genl_generate_id(void)
+{
+	static u16 id_gen_idx;
+	int overflowed = 0;
+
+	do {
+		if (id_gen_idx == 0)
+			id_gen_idx = GENL_MIN_ID;
+
+		if (++id_gen_idx > GENL_MAX_ID) {
+			if (!overflowed) {
+				overflowed = 1;
+				id_gen_idx = 0;
+				continue;
+			} else
+				return 0;
+		}
+
+	} while (genl_family_find_byid(id_gen_idx));
+
+	return id_gen_idx;
+}
+
+/**
+ * genl_register_ops - register generic netlink operations
+ * @family: generic netlink family
+ * @ops: operations to be registered
+ *
+ * Registers the specified operations and assigns them to the specified
+ * family. Either a doit or dumpit callback must be specified or the
+ * operation will fail. Only one operation structure per command
+ * identifier may be registered.
+ *
+ * See include/net/genetlink.h for more documenation on the operations
+ * structure.
+ *
+ * Returns 0 on success or a negative error code.
+ */
+int genl_register_ops(struct genl_family *family, struct genl_ops *ops)
+{
+	int err = -EINVAL;
+
+	if (ops->dumpit == NULL && ops->doit == NULL)
+		goto errout;
+
+	if (genl_get_cmd(ops->cmd, family)) {
+		err = -EEXIST;
+		goto errout;
+	}
+
+	genl_lock();
+	list_add_tail(&ops->ops_list, &family->ops_list);
+	genl_unlock();
+
+	genl_ctrl_event(CTRL_CMD_NEWOPS, ops);
+	err = 0;
+errout:
+	return err;
+}
+
+/**
+ * genl_unregister_ops - unregister generic netlink operations
+ * @family: generic netlink family
+ * @ops: operations to be unregistered
+ *
+ * Unregisters the specified operations and unassigns them from the
+ * specified family. The operation blocks until the current message
+ * processing has finished and doesn't start again until the
+ * unregister process has finished.
+ *
+ * Note: It is not necessary to unregister all operations before
+ *       unregistering the family, unregistering the family will cause
+ *       all assigned operations to be unregistered automatically.
+ *
+ * Returns 0 on success or a negative error code.
+ */
+int genl_unregister_ops(struct genl_family *family, struct genl_ops *ops)
+{
+	struct genl_ops *rc;
+
+	genl_lock();
+	list_for_each_entry(rc, &family->ops_list, ops_list) {
+		if (rc == ops) {
+			list_del(&ops->ops_list);
+			genl_unlock();
+			genl_ctrl_event(CTRL_CMD_DELOPS, ops);
+			return 0;
+		}
+	}
+	genl_unlock();
+
+	return -ENOENT;
+}
+
+/**
+ * genl_register_family - register a generic netlink family
+ * @family: generic netlink family
+ *
+ * Registers the specified family after validating it first. Only one
+ * family may be registered with the same family name or identifier.
+ * The family id may equal GENL_ID_GENERATE causing an unique id to
+ * be automatically generated and assigned.
+ *
+ * Return 0 on success or a negative error code.
+ */
+int genl_register_family(struct genl_family *family)
+{
+	int err = -EINVAL;
+
+	if (family->id && family->id < GENL_MIN_ID)
+		goto errout;
+
+	if (family->id > GENL_MAX_ID)
+		goto errout;
+
+	INIT_LIST_HEAD(&family->ops_list);
+
+	genl_lock();
+
+	if (genl_family_find_byname(family->name)) {
+		err = -EEXIST;
+		goto errout_locked;
+	}
+
+	if (genl_family_find_byid(family->id)) {
+		err = -EEXIST;
+		goto errout_locked;
+	}
+
+	if (!try_module_get(family->owner)) {
+		err = -EBUSY;
+		goto errout_locked;
+	}
+
+	if (family->id == GENL_ID_GENERATE) {
+		u16 newid = genl_generate_id();
+
+		if (!newid) {
+			err = -ENOMEM;
+			goto errout_locked;
+		}
+
+		family->id = newid;
+	}
+
+	if (family->maxattr) {
+		family->attrbuf = kmalloc((family->maxattr+1) *
+					sizeof(struct nlattr *), GFP_KERNEL);
+		if (family->attrbuf == NULL) {
+			err = -ENOMEM;
+			goto errout;
+		}
+	} else
+		family->attrbuf = NULL;
+
+	list_add_tail(&family->family_list, genl_family_chain(family->id));
+	genl_unlock();
+
+	genl_ctrl_event(CTRL_CMD_NEWFAMILY, family);
+
+	return 0;
+
+errout_locked:
+	genl_unlock();
+errout:
+	return err;
+}
+
+/**
+ * genl_unregister_family - unregister generic netlink family
+ * @family: generic netlink family
+ *
+ * Unregisters the specified family.
+ *
+ * Returns 0 on success or a negative error code.
+ */
+int genl_unregister_family(struct genl_family *family)
+{
+	struct genl_family *rc;
+
+	genl_lock();
+
+	list_for_each_entry(rc, genl_family_chain(family->id), family_list) {
+		if (family->id != rc->id || strcmp(rc->name, family->name))
+			continue;
+
+		list_del(&rc->family_list);
+		INIT_LIST_HEAD(&family->ops_list);
+		genl_unlock();
+
+		module_put(family->owner);
+		kfree(family->attrbuf);
+		genl_ctrl_event(CTRL_CMD_DELFAMILY, family);
+		return 0;
+	}
+
+	genl_unlock();
+
+	return -ENOENT;
+}
+
+static inline int genl_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
+			       int *errp)
+{
+	struct genl_ops *ops;
+	struct genl_family *family;
+	struct genl_info info;
+	struct genlmsghdr *hdr = nlmsg_data(nlh);
+	int hdrlen, err = -EINVAL;
+
+	if (!(nlh->nlmsg_flags & NLM_F_REQUEST))
+		goto ignore;
+
+	if (nlh->nlmsg_type < NLMSG_MIN_TYPE)
+		goto ignore;
+
+       	family = genl_family_find_byid(nlh->nlmsg_type);
+	if (family == NULL) {
+		err = -ENOENT;
+		goto errout;
+	}
+
+	hdrlen = GENL_HDRLEN + family->hdrsize;
+	if (nlh->nlmsg_len < nlmsg_msg_size(hdrlen))
+		goto errout;
+
+	ops = genl_get_cmd(hdr->cmd, family);
+	if (ops == NULL) {
+		err = -EOPNOTSUPP;
+		goto errout;
+	}
+
+	if ((ops->flags & GENL_ADMIN_PERM) && security_netlink_recv(skb)) {
+		err = -EPERM;
+		goto errout;
+	}
+
+	if (nlh->nlmsg_flags & NLM_F_DUMP) {
+		if (ops->dumpit == NULL) {
+			err = -EOPNOTSUPP;
+			goto errout;
+		}
+
+		*errp = err = netlink_dump_start(genl_sock, skb, nlh,
+						 ops->dumpit, NULL);
+		if (err == 0)
+			skb_pull(skb, min(NLMSG_ALIGN(nlh->nlmsg_len),
+					  skb->len));
+		return -1;
+	}
+
+	if (ops->doit == NULL) {
+		err = -EOPNOTSUPP;
+		goto errout;
+	}
+
+	if (family->attrbuf) {
+		err = nlmsg_parse(nlh, hdrlen, family->attrbuf, family->maxattr,
+				  ops->policy);
+		if (err < 0)
+			goto errout;
+	}
+
+	info.snd_seq = nlh->nlmsg_seq;
+	info.snd_pid = NETLINK_CB(skb).pid;
+	info.nlhdr = nlh;
+	info.genlhdr = nlmsg_data(nlh);
+	info.userhdr = nlmsg_data(nlh) + GENL_HDRLEN;
+	info.attrs = family->attrbuf;
+
+	*errp = err = ops->doit(skb, &info);
+	return err;
+
+ignore:
+	return 0;
+
+errout:
+	*errp = err;
+	return -1;
+}
+
+static void genl_rcv(struct sock *sk, int len)
+{
+	unsigned int qlen = 0;
+
+	do {
+		if (genl_trylock())
+			return;
+		netlink_run_queue(sk, &qlen, &genl_rcv_msg);
+		genl_unlock();
+	} while (qlen && genl_sock && genl_sock->sk_receive_queue.qlen);
+}
+
+/**************************************************************************
+ * Controller
+ **************************************************************************/
+
+static int ctrl_fill_info(struct genl_family *family, u32 pid, u32 seq,
+			  u32 flags, struct sk_buff *skb, u8 cmd)
+{
+	void *hdr;
+
+	hdr = genlmsg_put(skb, pid, seq, GENL_ID_CTRL, 0, flags, cmd,
+			  family->version);
+	if (hdr == NULL)
+		return -1;
+
+	NLA_PUT_STRING(skb, CTRL_ATTR_FAMILY_NAME, family->name);
+	NLA_PUT_U16(skb, CTRL_ATTR_FAMILY_ID, family->id);
+
+	return genlmsg_end(skb, hdr);
+
+nla_put_failure:
+	return genlmsg_cancel(skb, hdr);
+}
+
+static int ctrl_dumpfamily(struct sk_buff *skb, struct netlink_callback *cb)
+{
+
+	int i, n = 0;
+	struct genl_family *rt;
+	int chains_to_skip = cb->args[0];
+	int fams_to_skip = cb->args[1];
+
+	for (i = 0; i < GENL_FAM_TAB_SIZE; i++) {
+		if (i < chains_to_skip)
+			continue;
+		n = 0;
+		list_for_each_entry(rt, genl_family_chain(i), family_list) {
+			if (++n < fams_to_skip)
+				continue;
+			if (ctrl_fill_info(rt, NETLINK_CB(cb->skb).pid,
+					   cb->nlh->nlmsg_seq, NLM_F_MULTI,
+					   skb, CTRL_CMD_NEWFAMILY) < 0)
+				goto errout;
+		}
+
+		fams_to_skip = 0;
+	}
+
+errout:
+	cb->args[0] = i;
+	cb->args[1] = n;
+
+	return skb->len;
+}
+
+static struct sk_buff *ctrl_build_msg(struct genl_family *family, u32 pid,
+				      int seq, int cmd)
+{
+	struct sk_buff *skb;
+	int err;
+
+	skb = nlmsg_new(NLMSG_GOODSIZE);
+	if (skb == NULL)
+		return ERR_PTR(-ENOBUFS);
+
+	err = ctrl_fill_info(family, pid, seq, 0, skb, cmd);
+	if (err < 0) {
+		nlmsg_free(skb);
+		return ERR_PTR(err);
+	}
+
+	return skb;
+}
+
+static struct nla_policy ctrl_policy[CTRL_ATTR_MAX+1] __read_mostly = {
+	[CTRL_ATTR_FAMILY_ID]	= { .type = NLA_U16 },
+	[CTRL_ATTR_FAMILY_NAME]	= { .type = NLA_STRING },
+};
+
+static int ctrl_getfamily(struct sk_buff *skb, struct genl_info *info)
+{
+	struct sk_buff *msg;
+	struct genl_family *res = NULL;
+	int err = -EINVAL;
+
+	if (info->attrs[CTRL_ATTR_FAMILY_ID]) {
+		u16 id = nla_get_u16(info->attrs[CTRL_ATTR_FAMILY_ID]);
+		res = genl_family_find_byid(id);
+	}
+
+	if (info->attrs[CTRL_ATTR_FAMILY_NAME]) {
+		char name[GENL_NAMSIZ];
+
+		if (nla_strlcpy(name, info->attrs[CTRL_ATTR_FAMILY_NAME],
+				GENL_NAMSIZ) >= GENL_NAMSIZ)
+			goto errout;
+
+		res = genl_family_find_byname(name);
+	}
+
+	if (res == NULL) {
+		err = -ENOENT;
+		goto errout;
+	}
+
+	msg = ctrl_build_msg(res, info->snd_pid, info->snd_seq,
+			     CTRL_CMD_NEWFAMILY);
+	if (IS_ERR(msg)) {
+		err = PTR_ERR(msg);
+		goto errout;
+	}
+
+	err = genlmsg_unicast(msg, info->snd_pid);
+errout:
+	return err;
+}
+
+static int genl_ctrl_event(int event, void *data)
+{
+	struct sk_buff *msg;
+
+	if (genl_sock == NULL)
+		return 0;
+
+	switch (event) {
+	case CTRL_CMD_NEWFAMILY:
+	case CTRL_CMD_DELFAMILY:
+		msg = ctrl_build_msg(data, 0, 0, event);
+		if (IS_ERR(msg))
+			return PTR_ERR(msg);
+
+		genlmsg_multicast(msg, 0, GENL_ID_CTRL);
+		break;
+	}
+
+	return 0;
+}
+
+static struct genl_ops genl_ctrl_ops = {
+	.cmd		= CTRL_CMD_GETFAMILY,
+	.doit		= ctrl_getfamily,
+	.dumpit		= ctrl_dumpfamily,
+	.policy		= ctrl_policy,
+};
+
+static struct genl_family genl_ctrl = {
+	.id = GENL_ID_CTRL,
+	.name = "nlctrl",
+	.version = 0x1,
+	.maxattr = CTRL_ATTR_MAX,
+	.owner = THIS_MODULE,
+};
+
+static int __init genl_init(void)
+{
+	int i, err;
+
+	for (i = 0; i < GENL_FAM_TAB_SIZE; i++)
+		INIT_LIST_HEAD(&family_ht[i]);
+
+	err = genl_register_family(&genl_ctrl);
+	if (err < 0)
+		goto errout;
+
+	err = genl_register_ops(&genl_ctrl, &genl_ctrl_ops);
+	if (err < 0)
+		goto errout_register;
+
+	netlink_set_nonroot(NETLINK_GENERIC, NL_NONROOT_RECV);
+	genl_sock = netlink_kernel_create(NETLINK_GENERIC, GENL_MAX_ID,
+					  genl_rcv, THIS_MODULE);
+	if (genl_sock == NULL) {
+		panic("GENL: Cannot initialize generic netlink\n");
+		return -ENOMEM;
+	}
+
+	return 0;
+
+errout_register:
+	genl_unregister_family(&genl_ctrl);
+errout:
+	panic("GENL: Cannot register controller: %d\n", err);
+	return err;
+}
+
+subsys_initcall(genl_init);
+
+EXPORT_SYMBOL(genl_sock);
+EXPORT_SYMBOL(genl_register_ops);
+EXPORT_SYMBOL(genl_unregister_ops);
+EXPORT_SYMBOL(genl_register_family);
+EXPORT_SYMBOL(genl_unregister_family);