Linux内核由4.4升级到5.4做的一些改变（二）—

本文详细对比了Linux 4.4和5.4内核中Genetlink框架的改动，包括取消了`with_ops`扩展，新增了`nla_policy`字段，`GENL_ID_GENERATE`的修改以及`genlmsg_parse`函数的变化。这些改动影响了Genetlink家族的注册方式和错误处理机制，展示了内核对网络控制消息处理的优化和发展。

2.Generic Netlink

2.1 注册generic netlink family时取消了with_ops的扩展

因此在注册时需要先给genl_family赋值，再进行注册。

文件名 include/net/genetlink.h
4.4

struct genl_family {
	unsigned int		id;
	unsigned int		hdrsize;
	char			name[GENL_NAMSIZ];
	unsigned int		version;
	unsigned int		maxattr;
	bool			netnsok;
	bool			parallel_ops;
	int			(*pre_doit)(const struct genl_ops *ops,
					    struct sk_buff *skb,
					    struct genl_info *info);
	void			(*post_doit)(const struct genl_ops *ops,
					     struct sk_buff *skb,
					     struct genl_info *info);
	int			(*mcast_bind)(struct net *net, int group);
	void			(*mcast_unbind)(struct net *net, int group);
	struct nlattr **	attrbuf;	/* private */
	const struct genl_ops *	ops;		/* private */
	const struct genl_multicast_group *mcgrps; /* private */
	unsigned int		n_ops;		/* private */
	unsigned int		n_mcgrps;	/* private */
	unsigned int		mcgrp_offset;	/* private */
	struct list_head	family_list;	/* private */	//5.4中没有这个
	struct module		*module;
};
struct genl_ops {
	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);
	u8			cmd;
	u8			internal_flags;
	u8			flags;
};

static inline int genl_register_family(struct genl_family *family)
{
	family->module = THIS_MODULE;
	return __genl_register_family(family);
}
static inline int
_genl_register_family_with_ops_grps(struct genl_family *family,
				    const struct genl_ops *ops, size_t n_ops,
				    const struct genl_multicast_group *mcgrps,
				    size_t n_mcgrps)
{
	family->module = THIS_MODULE;
	family->ops = ops;
	family->n_ops = n_ops;
	family->mcgrps = mcgrps;
	family->n_mcgrps = n_mcgrps;
	return __genl_register_family(family);
}

#define genl_register_family_with_ops(family, ops)			\
	_genl_register_family_with_ops_grps((family),			\
					    (ops), ARRAY_SIZE(ops),	\
					    NULL, 0)
#define genl_register_family_with_ops_groups(family, ops, grps)	\
	_genl_register_family_with_ops_grps((family),			\
					    (ops), ARRAY_SIZE(ops),	\
					    (grps), ARRAY_SIZE(grps))

5.4

struct genl_family {
	int			id;		/* private */
	unsigned int		hdrsize;
	char			name[GENL_NAMSIZ];
	unsigned int		version;
	unsigned int		maxattr;
	bool			netnsok;
	bool			parallel_ops;
	const struct nla_policy *policy;   //多了这个！
	int			(*pre_doit)(const struct genl_ops *ops,
					    struct sk_buff *skb,
					    struct genl_info *info);
	void			(*post_doit)(const struct genl_ops *ops,
					     struct sk_buff *skb,
					     struct genl_info *info);
	int			(*mcast_bind)(struct net *net, int group);
	void			(*mcast_unbind)(struct net *net, int group);
	struct nlattr **	attrbuf;	/* private */
	const struct genl_ops *	ops;
	const struct genl_multicast_group *mcgrps;
	unsigned int		n_ops;
	unsigned int		n_mcgrps;
	unsigned int		mcgrp_offset;	/* private */
	struct module		*module;
};
struct genl_ops {
	int		       (*doit)(struct sk_buff *skb,
				       struct genl_info *info);
	int		       (*start)(struct netlink_callback *cb);
	int		       (*dumpit)(struct sk_buff *skb,
					 struct netlink_callback *cb);
	int		       (*done)(struct netlink_callback *cb);
	u8			cmd;
	u8			internal_flags;
	u8			flags;
	u8			validate;
};

int genl_register_family(struct genl_family *family);
int genl_unregister_family(const struct genl_family *family);

2.2 对GENL_ID_GENERATE进行了修改

文件名 include/linux/genetlink.h
4.4

#define NLMSG_MIN_TYPE		0x10	/* < 0x10: reserved control messages */
#define GENL_MIN_ID	NLMSG_MIN_TYPE
#define GENL_MAX_ID	1023

#define GENL_ID_GENERATE	0
#define GENL_ID_CTRL		NLMSG_MIN_TYPE
#define GENL_ID_VFS_DQUOT	(NLMSG_MIN_TYPE + 1)
#define GENL_ID_PMCRAID		(NLMSG_MIN_TYPE + 2)

5.4

#define NLMSG_MIN_TYPE		0x10	/* < 0x10: reserved control messages */
#define GENL_MIN_ID	NLMSG_MIN_TYPE
#define GENL_MAX_ID	1023

#define GENL_ID_CTRL		NLMSG_MIN_TYPE
#define GENL_ID_VFS_DQUOT	(NLMSG_MIN_TYPE + 1)
#define GENL_ID_PMCRAID		(NLMSG_MIN_TYPE + 2)
/* must be last reserved + 1 */
#define GENL_START_ALLOC	(NLMSG_MIN_TYPE + 3)

2.3 genlmsg_parse函数进行了修改

文件名 include/linux/genetlink.h
参数中增加了extack。
4.4

static inline int genlmsg_parse(const struct nlmsghdr *nlh,
				const struct genl_family *family,
				struct nlattr *tb[], int maxtype,
				const struct nla_policy *policy)
{
	return nlmsg_parse(nlh, family->hdrsize + GENL_HDRLEN, tb, maxtype,
			   policy);
}

5.4

static inline int genlmsg_parse(const struct nlmsghdr *nlh,
				const struct genl_family *family,
				struct nlattr *tb[], int maxtype,
				const struct nla_policy *policy,
				struct netlink_ext_ack *extack)
{
	return __nlmsg_parse(nlh, family->hdrsize + GENL_HDRLEN, tb, maxtype,
			     policy, NL_VALIDATE_STRICT, extack);
}

extack定义在genl_info中，看起来像是返回错误信息的。
4.4

struct genl_info {
	u32			snd_seq;
	u32			snd_portid;
	struct nlmsghdr *	nlhdr;
	struct genlmsghdr *	genlhdr;
	void *			userhdr;
	struct nlattr **	attrs;
	possible_net_t		_net;
	void *			user_ptr[2];
	struct sock *		dst_sk;
};

5.4

struct genl_info {
	u32			snd_seq;
	u32			snd_portid;
	struct nlmsghdr *	nlhdr;
	struct genlmsghdr *	genlhdr;
	void *			userhdr;
	struct nlattr **	attrs;
	possible_net_t		_net;
	void *			user_ptr[2];
	struct netlink_ext_ack *extack;	//这里！
};
/**
 * struct netlink_ext_ack - netlink extended ACK report struct
 * @_msg: message string to report - don't access directly, use
 *	%NL_SET_ERR_MSG
 * @bad_attr: attribute with error
 * @cookie: cookie data to return to userspace (for success)
 * @cookie_len: actual cookie data length
 */
struct netlink_ext_ack {
	const char *_msg;
	const struct nlattr *bad_attr;
	u8 cookie[NETLINK_MAX_COOKIE_LEN];
	u8 cookie_len;
};