本文基于下面两篇文章：
【 http://blog.chinaunix.net/uid-20273473-id-3137039.html 】
【 http://www.tuicool.com/articles/jE7nim 】
源码笔记：
CONTENTS
/linux-2.6.32.65/net/netlink/genetlink.c:
/*
* NETLINK Generic Netlink Family
*
* Authors: Jamal Hadi Salim
* Thomas Graf <tgraf@suug.ch>
* Johannes Berg <johannes@sipsolutions.net>
*/
#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 <linux/mutex.h>
#include <linux/bitmap.h>
#include <net/sock.h>
#include <net/genetlink.h>
/* 定义一个genetlink自己用的锁，当genetlink内部维护的变量发生变化时，可以用锁来保护。 */
static DEFINE_MUTEX(genl_mutex); /* serialization of message processing */
//加锁
static inline void genl_lock(void)
{
mutex_lock(&genl_mutex);
}
//解锁
static inline void genl_unlock(void)
{
mutex_unlock(&genl_mutex);
}
#define GENL_FAM_TAB_SIZE 16
#define GENL_FAM_TAB_MASK (GENL_FAM_TAB_SIZE - 1)
//定义16个内部实现组，将外部放到genetlink维护的family放到这16个组中，这样便于管理，提高查找速度。
static struct list_head family_ht[GENL_FAM_TAB_SIZE];
/*
* Bitmap of multicast groups that are currently in use.
*
* To avoid an allocation at boot of just one unsigned long,
* declare it global instead.
* Bit 0 is marked as already used since group 0 is invalid.
*/
static unsigned long mc_group_start = 0x1;
static unsigned long *mc_groups = &mc_group_start;
static unsigned long mc_groups_longs = 1;
static int genl_ctrl_event(int event, void *data);
//根据family的ID来确认这个family属于哪个组，这里简单的和15相与。
static inline unsigned int genl_family_hash(unsigned int id)
{
return id & GENL_FAM_TAB_MASK;
}
//根据family的ID来返回该family属于的组。
static inline struct list_head *genl_family_chain(unsigned int id)
{
return &family_ht[genl_family_hash(id)];
}
/*
判断一个family的ID是否在genetlink中，如果存在就返回该family的指针。
实现方式很简单，首先根据该ID确认所属的组，然后在该组中一个一个遍历查找。
*/
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;
}
/*
判断一个family的名字是否在genetlink中，如果存在就返回该family的指针。
由于genetlink中使用16个组来管理family，而通过名字不能定位到该family属于哪个组，因此这里需要遍历所有的组。
*/
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;
}
/*
在一个family中查找指定cmd对应的响应函数，简单遍历即可。
*/
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
*/
/*
为family生成一个ID。
实现方式为从GENL_MIN_ID开始累加，直到GENL_MAX_ID，如果找到一个ID之前没有注册，那就是它了。
如果到了GENL_MAX_ID还没有找到，就从0开始找，真找不到就返回0.
*/
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;
}
static struct genl_multicast_group notify_grp;
/**
* genl_register_mc_group - register a multicast group
*
* Registers the specified multicast group and notifies userspace
* about the new group.
*
* Returns 0 on success or a negative error code.
*
* @family: The generic netlink family the group shall be registered for.
* @grp: The group to register, must have a name.
*/
//为某个family注册一个组播操作，个人对组播没有太大要求，这里就跳过组播的笔记了。
int genl_register_mc_group(struct genl_family *family,
struct genl_multicast_group *grp)
{
int id;
unsigned long *new_groups;
int err = 0;
BUG_ON(grp->name[0] == '\0');
genl_lock();
/* special-case our own group */
if (grp == ¬ify_grp)
id = GENL_ID_CTRL;
else
id = find_first_zero_bit(mc_groups,
mc_groups_longs * BITS_PER_LONG);
if (id >= mc_groups_longs * BITS_PER_LONG) {
size_t nlen = (mc_groups_longs + 1) * sizeof(unsigned long);
if (mc_groups == &mc_group_start) {
new_groups = kzalloc(nlen, GFP_KERNEL);
if (!new_groups) {
err = -ENOMEM;
goto out;
}
mc_groups = new_groups;
*mc_groups = mc_group_start;
} else {
new_groups = krealloc(mc_groups, nlen, GFP_KERNEL);
if (!new_groups) {
err = -ENOMEM;
goto out;
}
mc_groups = new_groups;
mc_groups[mc_groups_longs] = 0;
}
mc_groups_longs++;
}
if (family->netnsok) {
struct net *net;
netlink_table_grab();
rcu_read_lock();
for_each_net_rcu(net) {
err = __netlink_change_ngroups(net->genl_sock,
mc_groups_longs * BITS_PER_LONG);
if (err) {
/*
* No need to roll back, can only fail if
* memory allocation fails and then the
* number of _possible_ groups has been
* increased on some sockets which is ok.
*/
rcu_read_unlock();
netlink_table_ungrab();
goto out;
}
}
rcu_read_unlock();
netlink_table_ungrab();
} else {
err = netlink_change_ngroups(init_net.genl_sock,
mc_groups_longs * BITS_PER_LONG);
if (err)
goto out;
}
grp->id = id;
set_bit(id, mc_groups);
list_add_tail(&grp->list, &family->mcast_groups);
grp->family = family;
genl_ctrl_event(CTRL_CMD_NEWMCAST_GRP, grp);
out:
genl_unlock();
return err;
}
EXPORT_SYMBOL(genl_register_mc_group);
static void __genl_unregister_mc_group(struct genl_family *family,
struct genl_multicast_group *grp)
{
struct net *net;
BUG_ON(grp->family != family);
netlink_table_grab();
rcu_read_lock();
for_each_net_rcu(net)
__netlink_clear_multicast_users(net->genl_sock, grp->id);
rcu_read_unlock();
netlink_table_ungrab();
clear_bit(grp->id, mc_groups);
list_del(&grp->list);
genl_ctrl_event(CTRL_CMD_DELMCAST_GRP, grp);
grp->id = 0;
grp->family = NULL;
}
/**
* genl_unregister_mc_group - unregister a multicast group
*
* Unregisters the specified multicast group and notifies userspace
* about it. All current listeners on the group are removed.
*
* Note: It is not necessary to unregister all multicast groups before
* unregistering the family, unregistering the family will cause
* all assigned multicast groups to be unregistered automatically.
*
* @family: Generic netlink family the group belongs to.
* @grp: The group to unregister, must have been registered successfully
* previously.
*/
void genl_unregister_mc_group(struct genl_family *family,
struct genl_multicast_group *grp)
{
genl_lock();
__genl_unregister_mc_group(family, grp);
genl_unlock();
}
EXPORT_SYMBOL(genl_unregister_mc_group);
static void genl_unregister_mc_groups(struct genl_family *family)
{
struct genl_multicast_group *grp, *tmp;
list_for_each_entry_safe(grp, tmp, &family->mcast_groups, list)
__genl_unregister_mc_group(family, grp);
}
/**
* 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.
*/
//为某个family注册一个操作
int genl_register_ops(struct genl_family *family, struct genl_ops *ops)
{
int err = -EINVAL;
if (ops->dumpit == NULL && ops->doit == NULL)
goto errout;
//不能重复注册
if (genl_get_cmd(ops->cmd, family)) {
err = -EEXIST;
goto errout;
}
//根据支持的操作来标记下该操作结构体
if (ops->dumpit)
ops->flags |= GENL_CMD_CAP_DUMP;
if (ops->doit)
ops->flags |= GENL_CMD_CAP_DO;
if (ops->policy)
ops->flags |= GENL_CMD_CAP_HASPOL;
genl_lock();//锁一下，然后将该操作结构体添加到该family的操作列表中。
list_add_tail(&ops->ops_list, &family->ops_list);
genl_unlock();
//给自己发送一个事件，说明有新的ops加入，这样外部用户（一般是用户socket）可以读取新加入的ops信息
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.
*/
//为某个family解除注册一个操作
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.
*/
//向genetlink中注册一个family
int genl_register_family(struct genl_family *family)
{
int err = -EINVAL;
//family的ID不能随便赋值。
if (family->id && family->id < GENL_MIN_ID)
goto errout;
if (family->id > GENL_MAX_ID)
goto errout;
//初始化family中的链表头
INIT_LIST_HEAD(&family->ops_list);
INIT_LIST_HEAD(&family->mcast_groups);
genl_lock();//锁一下
//名字不能重复
if (genl_family_find_byname(family->name)) {
err = -EEXIST;
goto errout_locked;
}
//ID不能重复
if (genl_family_find_byid(family->id)) {
err = -EEXIST;
goto errout_locked;
}
//如果ID为GENL_ID_GENERATE，说明希望genetlink为它分配一个
if (family->id == GENL_ID_GENERATE) {
u16 newid = genl_generate_id();
if (!newid) {
err = -ENOMEM;
goto errout_locked;
}
family->id = newid;//分配一个新的ID
}
if (family->maxattr) {
family->attrbuf = kmalloc((family->maxattr+1) *
sizeof(struct nlattr *), GFP_KERNEL);
if (family->attrbuf == NULL) {
err = -ENOMEM;
goto errout_locked;
}
} else
family->attrbuf = NULL;
//根据ID来把该family加入到指定的组中。
list_add_tail(&family->family_list, genl_family_chain(family->id));
genl_unlock();
//给自己发送一个事件，说明有新的family加入，这样外部用户（一般是用户socket）可以读取新加入的family信息
genl_ctrl_event(CTRL_CMD_NEWFAMILY, family);
return 0;
errout_locked:
genl_unlock();
errout:
return err;
}
/**
* genl_register_family_with_ops - register a generic netlink family
* @family: generic netlink family
* @ops: operations to be registered
* @n_ops: number of elements to register
*
* Registers the specified family and operations from the specified table.
* 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.
*
* Either a doit or dumpit callback must be specified for every registered
* operation or the function will fail. Only one operation structure per
* command identifier may be registered.
*
* See include/net/genetlink.h for more documenation on the operations
* structure.
*
* This is equivalent to calling genl_register_family() followed by
* genl_register_ops() for every operation entry in the table taking
* care to unregister the family on error path.
*
* Return 0 on success or a negative error code.
*/
//整合后的方法，先注册一个family，然后为family注册一个操作数组，即ops是数组头
int genl_register_family_with_ops(struct genl_family *family,
struct genl_ops *ops, size_t n_ops)
{
int err, i;
//先注册family
err = genl_register_family(family);
if (err)
return err;
//遍历数组，将里面的操作结构体注册到family中
for (i = 0; i < n_ops; ++i, ++ops) {
err = genl_register_ops(family, ops);
if (err)
goto err_out;
}
return 0;
err_out:
genl_unregister_family(family);
return err;
}
EXPORT_SYMBOL(genl_register_family_with_ops);
/**
* genl_unregister_family - unregister generic netlink family
* @family: generic netlink family
*
* Unregisters the specified family.
*
* Returns 0 on success or a negative error code.
*/
//解除注册一个family
int genl_unregister_family(struct genl_family *family)
{
struct genl_family *rc;
genl_lock();
genl_unregister_mc_groups(family);
//先看下这个family是不是在genentlink中，ID和名字都要校验
list_for_each_entry(rc, genl_family_chain(family->id), family_list) {
if (family->id != rc->id || strcmp(rc->name, family->name))
continue;
//有，就从genetlink中删掉。
list_del(&rc->family_list);
//这里直接重新初始化操作列表，而不是循环删除。
INIT_LIST_HEAD(&family->ops_list);
genl_unlock();
kfree(family->attrbuf);
genl_ctrl_event(CTRL_CMD_DELFAMILY, family);
return 0;
}
genl_unlock();
return -ENOENT;
}
//从netlink中收到数据，看下是发给哪个family的
static int genl_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
{
struct genl_ops *ops;
struct genl_family *family;
struct net *net = sock_net(skb->sk);
struct genl_info info;
struct genlmsghdr *hdr = nlmsg_data(nlh);
int hdrlen, err;
//从nlh中找到对应的family
family = genl_family_find_byid(nlh->nlmsg_type);
if (family == NULL)
return -ENOENT;
/* this family doesn't exist in this netns */
if (!family->netnsok && !net_eq(net, &init_net))
return -ENOENT;
hdrlen = GENL_HDRLEN + family->hdrsize;
if (nlh->nlmsg_len < nlmsg_msg_size(hdrlen))
return -EINVAL;
//从hdr中找到对应的操作
ops = genl_get_cmd(hdr->cmd, family);
if (ops == NULL)
return -EOPNOTSUPP;
if ((ops->flags & GENL_ADMIN_PERM) &&
security_netlink_recv(skb, CAP_NET_ADMIN))
return -EPERM;
//如果nlh中表明了需要dump操作，但是dump操作并没有被注册，就报错。
if (nlh->nlmsg_flags & NLM_F_DUMP) {
if (ops->dumpit == NULL)
return -EOPNOTSUPP;
genl_unlock();
err = netlink_dump_start(net->genl_sock, skb, nlh,
ops->dumpit, ops->done);
genl_lock();
return err;
}
if (ops->doit == NULL)
return -EOPNOTSUPP;
if (family->attrbuf) {
err = nlmsg_parse(nlh, hdrlen, family->attrbuf, family->maxattr,
ops->policy);
if (err < 0)
return err;
}
// 生成info，然后发给doit操作。
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;
genl_info_net_set(&info, net);
return ops->doit(skb, &info);
}
static void genl_rcv(struct sk_buff *skb)
{
genl_lock();
netlink_rcv_skb(skb, &genl_rcv_msg);
genl_unlock();
}
/**************************************************************************
* Controller
**************************************************************************/
//genetlink自己注册一个管理family，用来管理注册到genetlink中的其他family
static struct genl_family genl_ctrl = {
.id = GENL_ID_CTRL,
.name = "nlctrl",
.version = 0x2,
.maxattr = CTRL_ATTR_MAX,
.netnsok = true,
};
//工具函数 将某个family的信息放到skb中，包括操作列表和组播信息
static int ctrl_fill_info(struct genl_family *family, u32 pid, u32 seq,
u32 flags, struct sk_buff *skb, u8 cmd)
{
void *hdr;
//开始构造
hdr = genlmsg_put(skb, pid, seq, &genl_ctrl, flags, cmd);
if (hdr == NULL)
return -1;
//将family的信息防盗skb中
NLA_PUT_STRING(skb, CTRL_ATTR_FAMILY_NAME, family->name);
NLA_PUT_U16(skb, CTRL_ATTR_FAMILY_ID, family->id);
NLA_PUT_U32(skb, CTRL_ATTR_VERSION, family->version);
NLA_PUT_U32(skb, CTRL_ATTR_HDRSIZE, family->hdrsize);
NLA_PUT_U32(skb, CTRL_ATTR_MAXATTR, family->maxattr);
//遍历操作列表，将每个操作项的信息都放到skb中
if (!list_empty(&family->ops_list)) {
struct nlattr *nla_ops;
struct genl_ops *ops;
int idx = 1;
nla_ops = nla_nest_start(skb, CTRL_ATTR_OPS);
if (nla_ops == NULL)
goto nla_put_failure;
list_for_each_entry(ops, &family->ops_list, ops_list) {
struct nlattr *nest;
nest = nla_nest_start(skb, idx++);
if (nest == NULL)
goto nla_put_failure;
NLA_PUT_U32(skb, CTRL_ATTR_OP_ID, ops->cmd);
NLA_PUT_U32(skb, CTRL_ATTR_OP_FLAGS, ops->flags);
nla_nest_end(skb, nest);
}
nla_nest_end(skb, nla_ops);
}
//遍历组播列表，将组播信息放到skb中
if (!list_empty(&family->mcast_groups)) {
struct genl_multicast_group *grp;
struct nlattr *nla_grps;
int idx = 1;
nla_grps = nla_nest_start(skb, CTRL_ATTR_MCAST_GROUPS);
if (nla_grps == NULL)
goto nla_put_failure;
list_for_each_entry(grp, &family->mcast_groups, list) {
struct nlattr *nest;
nest = nla_nest_start(skb, idx++);
if (nest == NULL)
goto nla_put_failure;
NLA_PUT_U32(skb, CTRL_ATTR_MCAST_GRP_ID, grp->id);
NLA_PUT_STRING(skb, CTRL_ATTR_MCAST_GRP_NAME,
grp->name);
nla_nest_end(skb, nest);
}
nla_nest_end(skb, nla_grps);
}
//结束构造
return genlmsg_end(skb, hdr);
nla_put_failure:
genlmsg_cancel(skb, hdr);
return -EMSGSIZE;
}
//工具函数 将组播信息放到skb中
static int ctrl_fill_mcgrp_info(struct genl_multicast_group *grp, u32 pid,
u32 seq, u32 flags, struct sk_buff *skb,
u8 cmd)
{
void *hdr;
struct nlattr *nla_grps;
struct nlattr *nest;
hdr = genlmsg_put(skb, pid, seq, &genl_ctrl, flags, cmd);
if (hdr == NULL)
return -1;
NLA_PUT_STRING(skb, CTRL_ATTR_FAMILY_NAME, grp->family->name);
NLA_PUT_U16(skb, CTRL_ATTR_FAMILY_ID, grp->family->id);
nla_grps = nla_nest_start(skb, CTRL_ATTR_MCAST_GROUPS);
if (nla_grps == NULL)
goto nla_put_failure;
nest = nla_nest_start(skb, 1);
if (nest == NULL)
goto nla_put_failure;
NLA_PUT_U32(skb, CTRL_ATTR_MCAST_GRP_ID, grp->id);
NLA_PUT_STRING(skb, CTRL_ATTR_MCAST_GRP_NAME,
grp->name);
nla_nest_end(skb, nest);
nla_nest_end(skb, nla_grps);
return genlmsg_end(skb, hdr);
nla_put_failure:
genlmsg_cancel(skb, hdr);
return -EMSGSIZE;
}
//遍历genetlink中的所有的family，将里面的信息放到skb中
//这里内部调用了ctrl_fill_info函数
static int ctrl_dumpfamily(struct sk_buff *skb, struct netlink_callback *cb)
{
int i, n = 0;
struct genl_family *rt;
struct net *net = sock_net(skb->sk);
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 (!rt->netnsok && !net_eq(net, &init_net))
continue;
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;
}
//将某个family的信息放到skb中，这里的skb是内部申请的
static struct sk_buff *ctrl_build_family_msg(struct genl_family *family,
u32 pid, int seq, u8 cmd)
{
struct sk_buff *skb;
int err;
skb = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL);
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;
}
//将组播信息放到skb中，这里的skb是内部申请的
static struct sk_buff *ctrl_build_mcgrp_msg(struct genl_multicast_group *grp,
u32 pid, int seq, u8 cmd)
{
struct sk_buff *skb;
int err;
skb = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL);
if (skb == NULL)
return ERR_PTR(-ENOBUFS);
err = ctrl_fill_mcgrp_info(grp, pid, seq, 0, skb, cmd);
if (err < 0) {
nlmsg_free(skb);
return ERR_PTR(err);
}
return skb;
}
static const struct nla_policy ctrl_policy[CTRL_ATTR_MAX+1] = {
[CTRL_ATTR_FAMILY_ID] = { .type = NLA_U16 },
[CTRL_ATTR_FAMILY_NAME] = { .type = NLA_NUL_STRING,
.len = GENL_NAMSIZ - 1 },
};
/* 查找family */
static int ctrl_getfamily(struct sk_buff *skb, struct genl_info *info)
{
struct sk_buff *msg;
struct genl_family *res = NULL;
int err = -EINVAL;
//如果info中带了ID，就看下这个ID是否有效。
if (info->attrs[CTRL_ATTR_FAMILY_ID]) {
u16 id = nla_get_u16(info->attrs[CTRL_ATTR_FAMILY_ID]);
res = genl_family_find_byid(id);
err = -ENOENT;
}
//如果info中带的是name，就根据name查找对应的ID
if (info->attrs[CTRL_ATTR_FAMILY_NAME]) {
char *name;
name = nla_data(info->attrs[CTRL_ATTR_FAMILY_NAME]);
res = genl_family_find_byname(name);
err = -ENOENT;
}
if (res == NULL)
return err;
if (!res->netnsok && !net_eq(genl_info_net(info), &init_net)) {
/* family doesn't exist here */
return -ENOENT;
}
//将找到的family防盗一个skb中
msg = ctrl_build_family_msg(res, info->snd_pid, info->snd_seq,
CTRL_CMD_NEWFAMILY);
if (IS_ERR(msg))
return PTR_ERR(msg);
//通过netlink将该信息返回，一般是返回用户态程序。
return genlmsg_reply(msg, info);
}
/*
内部工具函数，当genetlink中管理的family发生变化时，可以生成对应的信息发送到netlink中，
这样外部程序（一般是用户socket）可以直接获取，而不用在主动发送信息获取。
*/
static int genl_ctrl_event(int event, void *data)
{
struct sk_buff *msg;
struct genl_family *family;
struct genl_multicast_group *grp;
/* genl is still initialising */
if (!init_net.genl_sock)
return 0;
switch (event) {
case CTRL_CMD_NEWFAMILY:
case CTRL_CMD_DELFAMILY:
family = data;
msg = ctrl_build_family_msg(family, 0, 0, event);
break;
case CTRL_CMD_NEWMCAST_GRP:
case CTRL_CMD_DELMCAST_GRP:
grp = data;
family = grp->family;
msg = ctrl_build_mcgrp_msg(data, 0, 0, event);
break;
default:
return -EINVAL;
}
if (IS_ERR(msg))
return PTR_ERR(msg);
if (!family->netnsok) {
genlmsg_multicast_netns(&init_net, msg, 0,
GENL_ID_CTRL, GFP_KERNEL);
} else {
rcu_read_lock();
genlmsg_multicast_allns(msg, 0, GENL_ID_CTRL, GFP_ATOMIC);
rcu_read_unlock();
}
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_multicast_group notify_grp = {
.name = "notify",
};
static int __net_init genl_pernet_init(struct net *net)
{
/*
genetlink其实是使用netlink的一个模块，它内部的实现是基于netlink的，因此这里初始化时会在netlink中注册genetlink方法。
*/
/* we'll bump the group number right afterwards */
net->genl_sock = netlink_kernel_create(net, NETLINK_GENERIC, 0,
genl_rcv, &genl_mutex,
THIS_MODULE);
if (!net->genl_sock && net_eq(net, &init_net))
panic("GENL: Cannot initialize generic netlink\n");
if (!net->genl_sock)
return -ENOMEM;
return 0;
}
static void __net_exit genl_pernet_exit(struct net *net)
{
netlink_kernel_release(net->genl_sock);
net->genl_sock = NULL;
}
static struct pernet_operations genl_pernet_ops = {
.init = genl_pernet_init,
.exit = genl_pernet_exit,
};
//genetlink模块初始化函数
static int __init genl_init(void)
{
int i, err;
//首先初始化好16个管理组
for (i = 0; i < GENL_FAM_TAB_SIZE; i++)
INIT_LIST_HEAD(&family_ht[i]);
//将genetlink管理family注册到genetlink中
err = genl_register_family(&genl_ctrl);
if (err < 0)
goto problem;
/*
注册操作,这里外部对于genetlink的支持的操作只有一个，就是根据family的name查找对应的ID，
或者根据family的ID来查找是否有该family注册到genetlink中。
原因为当family注册到genetlink中时，一般都是自动获取ID的，这样外部的程序是不知道ID是多少的。
*/
err = genl_register_ops(&genl_ctrl, &genl_ctrl_ops);
if (err < 0)
goto problem;
netlink_set_nonroot(NETLINK_GENERIC, NL_NONROOT_RECV);
//注册命名空间
err = register_pernet_subsys(&genl_pernet_ops);
if (err)
goto problem;
//注册组播操作
err = genl_register_mc_group(&genl_ctrl, ¬ify_grp);
if (err < 0)
goto problem;
return 0;
problem:
panic("GENL: Cannot register controller: %d\n", err);
}
subsys_initcall(genl_init);
EXPORT_SYMBOL(genl_register_ops);
EXPORT_SYMBOL(genl_unregister_ops);
EXPORT_SYMBOL(genl_register_family);
EXPORT_SYMBOL(genl_unregister_family);
static int genlmsg_mcast(struct sk_buff *skb, u32 pid, unsigned long group,
gfp_t flags)
{
struct sk_buff *tmp;
struct net *net, *prev = NULL;
int err;
for_each_net_rcu(net) {
if (prev) {
tmp = skb_clone(skb, flags);
if (!tmp) {
err = -ENOMEM;
goto error;
}
err = nlmsg_multicast(prev->genl_sock, tmp,
pid, group, flags);
if (err)
goto error;
}
prev = net;
}
return nlmsg_multicast(prev->genl_sock, skb, pid, group, flags);
error:
kfree_skb(skb);
return err;
}
int genlmsg_multicast_allns(struct sk_buff *skb, u32 pid, unsigned int group,
gfp_t flags)
{
return genlmsg_mcast(skb, pid, group, flags);
}
EXPORT_SYMBOL(genlmsg_multicast_allns);
/linux-2.6.32.65/include/net/genetlink.h:
#ifndef __NET_GENERIC_NETLINK_H
#define __NET_GENERIC_NETLINK_H
#include <linux/genetlink.h>
#include <net/netlink.h>
#include <net/net_namespace.h>
/**
* struct genl_multicast_group - generic netlink multicast group
* @name: name of the multicast group, names are per-family
* @id: multicast group ID, assigned by the core, to use with
* genlmsg_multicast().
* @list: list entry for linking
* @family: pointer to family, need not be set before registering
*/
struct genl_multicast_group
{
struct genl_family *family; /* private */
struct list_head list; /* private */
char name[GENL_NAMSIZ];
u32 id;
};
/**
* 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
* @netnsok: set to true if the family can handle network
* namespaces and should be presented in all of them
* @attrbuf: buffer to store parsed attributes
* @ops_list: list of all assigned operations
* @family_list: family list
* @mcast_groups: multicast groups list
*/
struct genl_family
{
unsigned int id;
unsigned int hdrsize;
char name[GENL_NAMSIZ];
unsigned int version;
unsigned int maxattr;
bool netnsok;
struct nlattr ** attrbuf; /* private */
struct list_head ops_list; /* private */
struct list_head family_list; /* private */
struct list_head mcast_groups; /* private */
};
/**
* 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;
#ifdef CONFIG_NET_NS
struct net * _net;
#endif
};
#ifdef CONFIG_NET_NS
static inline struct net *genl_info_net(struct genl_info *info)
{
return info->_net;
}
static inline void genl_info_net_set(struct genl_info *info, struct net *net)
{
info->_net = net;
}
#else
static inline struct net *genl_info_net(struct genl_info *info)
{
return &init_net;
}
static inline void genl_info_net_set(struct genl_info *info, struct net *net)
{
}
#endif
/**
* struct genl_ops - generic netlink operations
* @cmd: command identifier
* @flags: flags
* @policy: attribute validation policy
* @doit: standard command callback
* @dumpit: callback for dumpers
* @done: completion callback for dumps
* @ops_list: operations list
*/
struct genl_ops
{
u8 cmd;
unsigned int flags;
const struct nla_policy *policy;
int (*doit)(struct sk_buff *skb,
struct genl_info *info);
int (*dumpit)(struct sk_buff *skb,
struct netlink_callback *cb);
int (*done)(struct netlink_callback *cb);
struct list_head ops_list;
};
extern int genl_register_family(struct genl_family *family);
extern int genl_register_family_with_ops(struct genl_family *family,
struct genl_ops *ops, size_t n_ops);
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 int genl_register_mc_group(struct genl_family *family,
struct genl_multicast_group *grp);
extern void genl_unregister_mc_group(struct genl_family *family,
struct genl_multicast_group *grp);
/**
* 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)
* @family: generic netlink family
* @flags netlink message flags
* @cmd: generic netlink command
*
* Returns pointer to user specific header
*/
static inline void *genlmsg_put(struct sk_buff *skb, u32 pid, u32 seq,
struct genl_family *family, int flags, u8 cmd)
{
struct nlmsghdr *nlh;
struct genlmsghdr *hdr;
nlh = nlmsg_put(skb, pid, seq, family->id, GENL_HDRLEN +
family->hdrsize, flags);
if (nlh == NULL)
return NULL;
hdr = nlmsg_data(nlh);
hdr->cmd = cmd;
hdr->version = family->version;
hdr->reserved = 0;
return (char *) hdr + GENL_HDRLEN;
}
/**
* genlmsg_put_reply - Add generic netlink header to a reply message
* @skb: socket buffer holding the message
* @info: receiver info
* @family: generic netlink family
* @flags: netlink message flags
* @cmd: generic netlink command
*
* Returns pointer to user specific header
*/
static inline void *genlmsg_put_reply(struct sk_buff *skb,
struct genl_info *info,
struct genl_family *family,
int flags, u8 cmd)
{
return genlmsg_put(skb, info->snd_pid, info->snd_seq, family,
flags, cmd);
}
/**
* 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 void genlmsg_cancel(struct sk_buff *skb, void *hdr)
{
nlmsg_cancel(skb, hdr - GENL_HDRLEN - NLMSG_HDRLEN);
}
/**
* genlmsg_multicast_netns - multicast a netlink message to a specific netns
* @net: the net namespace
* @skb: netlink message as socket buffer
* @pid: own netlink pid to avoid sending to yourself
* @group: multicast group id
* @flags: allocation flags
*/
static inline int genlmsg_multicast_netns(struct net *net, struct sk_buff *skb,
u32 pid, unsigned int group, gfp_t flags)
{
return nlmsg_multicast(net->genl_sock, skb, pid, group, flags);
}
/**
* genlmsg_multicast - multicast a netlink message to the default netns
* @skb: netlink message as socket buffer
* @pid: own netlink pid to avoid sending to yourself
* @group: multicast group id
* @flags: allocation flags
*/
static inline int genlmsg_multicast(struct sk_buff *skb, u32 pid,
unsigned int group, gfp_t flags)
{
return genlmsg_multicast_netns(&init_net, skb, pid, group, flags);
}
/**
* genlmsg_multicast_allns - multicast a netlink message to all net namespaces
* @skb: netlink message as socket buffer
* @pid: own netlink pid to avoid sending to yourself
* @group: multicast group id
* @flags: allocation flags
*
* This function must hold the RTNL or rcu_read_lock().
*/
int genlmsg_multicast_allns(struct sk_buff *skb, u32 pid,
unsigned int group, gfp_t flags);
/**
* 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 net *net, struct sk_buff *skb, u32 pid)
{
return nlmsg_unicast(net->genl_sock, skb, pid);
}
/**
* genlmsg_reply - reply to a request
* @skb: netlink message to be sent back
* @info: receiver information
*/
static inline int genlmsg_reply(struct sk_buff *skb, struct genl_info *info)
{
return genlmsg_unicast(genl_info_net(info), skb, info->snd_pid);
}
/**
* gennlmsg_data - head of message payload
* @gnlh: genetlink messsage header
*/
static inline void *genlmsg_data(const struct genlmsghdr *gnlh)
{
return ((unsigned char *) gnlh + GENL_HDRLEN);
}
/**
* genlmsg_len - length of message payload
* @gnlh: genetlink message header
*/
static inline int genlmsg_len(const struct genlmsghdr *gnlh)
{
struct nlmsghdr *nlh = (struct nlmsghdr *)((unsigned char *)gnlh -
NLMSG_HDRLEN);
return (nlh->nlmsg_len - GENL_HDRLEN - NLMSG_HDRLEN);
}
/**
* genlmsg_msg_size - length of genetlink message not including padding
* @payload: length of message payload
*/
static inline int genlmsg_msg_size(int payload)
{
return GENL_HDRLEN + payload;
}
/**
* genlmsg_total_size - length of genetlink message including padding
* @payload: length of message payload
*/
static inline int genlmsg_total_size(int payload)
{
return NLMSG_ALIGN(genlmsg_msg_size(payload));
}
/**
* genlmsg_new - Allocate a new generic netlink message
* @payload: size of the message payload
* @flags: the type of memory to allocate.
*/
static inline struct sk_buff *genlmsg_new(size_t payload, gfp_t flags)
{
return nlmsg_new(genlmsg_total_size(payload), flags);
}
#endif /* __NET_GENERIC_NETLINK_H */
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