iw是Linux比较推荐的无线网络配置工具，它基于新的交互框架nl80211，是用于取代iwconfig等以前基于wext的配置工具。
官网链接【 https://wireless.wiki.kernel.org/en/users/documentation/iw 】
作者最近使用到了iw里面的一些小众功能，这里笔记下它的基本框架吧，看下它是如何和驱动交互的。
PS：作者没有使用linux进行实际的编译和执行，因此仅仅通过代码阅读来分析，而cmd的注册使用了段操作，作者分析可能有问题，这里先说明下~后面用linux编译后再更新~~
从官网可以下载最新的iw源码，作者这里是iw4.3，解压缩。
首先进入iw.c中，这里有main函数的入口，简单笔记下：
int main(int argc, char **argv)
{
struct nl80211_state nlstate;
int err;
const struct cmd *cmd = NULL;
/* 首先计算下一个cmd的大小是多少，便于后续偏移 */
/* calculate command size including padding */
cmd_size = abs((long)&__section_set - (long)&__section_get);
/* strip off self */
argc--;
argv0 = *argv++;
if (argc > 0 && strcmp(*argv, "--debug") == 0) {
iw_debug = 1;
argc--;
argv++;
}
if (argc > 0 && strcmp(*argv, "--version") == 0) {
version();
return 0;
}
/* need to treat "help" command specially so it works w/o nl80211 */
if (argc == 0 || strcmp(*argv, "help") == 0) {
usage(argc - 1, argv + 1);
return 0;
}
/* 初始化用户态的nl80211接口 */
err = nl80211_init(&nlstate);
if (err)
return 1;
/* 由于iw命令支持省略dev/phy 关键字，因此解析起来会复杂一点 */
if (strcmp(*argv, "dev") == 0 && argc > 1) {
argc--;
argv++;
err = __handle_cmd(&nlstate, II_NETDEV, argc, argv, &cmd);
} else if (strncmp(*argv, "phy", 3) == 0 && argc > 1) {
if (strlen(*argv) == 3) {
argc--;
argv++;
err = __handle_cmd(&nlstate, II_PHY_NAME, argc, argv, &cmd);
} else if (*(*argv + 3) == '#')
err = __handle_cmd(&nlstate, II_PHY_IDX, argc, argv, &cmd);
else
goto detect;
} else if (strcmp(*argv, "wdev") == 0 && argc > 1) {
argc--;
argv++;
err = __handle_cmd(&nlstate, II_WDEV, argc, argv, &cmd);
} else {
int idx;
enum id_input idby = II_NONE;
detect:
if ((idx = if_nametoindex(argv[0])) != 0)
idby = II_NETDEV;
else if ((idx = phy_lookup(argv[0])) >= 0)
idby = II_PHY_NAME;
err = __handle_cmd(&nlstate, idby, argc, argv, &cmd);
}
/* 出错了，就打印下help文档 */
if (err == 1) {
if (cmd)
usage_cmd(cmd);
else
usage(0, NULL);
} else if (err < 0)
fprintf(stderr, "command failed: %s (%d)\n", strerror(-err), err);
/* 关掉用户态的nl80211接口 */
nl80211_cleanup(&nlstate);
return err;
}
整个iw框架就是这样，初始化nl接口，解析并处理命令，然后关闭nl接口。
这里继续分析，首先看下这里是如何初始化nl接口的。
iw.c中继续分析，
/* 初始化用户态的nl80211接口 */
static int nl80211_init(struct nl80211_state *state)
{
int err;
/* 初始化socket 注意这里其实是genetlink子框架 */
state->nl_sock = nl_socket_alloc();
if (!state->nl_sock) {
fprintf(stderr, "Failed to allocate netlink socket.\n");
return -ENOMEM;
}
nl_socket_set_buffer_size(state->nl_sock, 8192, 8192);
if (genl_connect(state->nl_sock)) {
fprintf(stderr, "Failed to connect to generic netlink.\n");
err = -ENOLINK;
goto out_handle_destroy;
}
/* 看下内核态有没有对应的已经注册的genetlink框架 */
state->nl80211_id = genl_ctrl_resolve(state->nl_sock, "nl80211");
if (state->nl80211_id < 0) {
fprintf(stderr, "nl80211 not found.\n");
err = -ENOENT;
goto out_handle_destroy;
}
return 0;
out_handle_destroy:
nl_socket_free(state->nl_sock);
return err;
}
这里我们插播一段代码，在Linux2.6.32中，查看nl80211.c,可以发现如下代码：
/* the netlink family */
static struct genl_family nl80211_fam = {
.id = GENL_ID_GENERATE, /* don't bother with a hardcoded ID */
.name = "nl80211", /* have users key off the name instead */
.hdrsize = 0, /* no private header */
.version = 1, /* no particular meaning now */
.maxattr = NL80211_ATTR_MAX,
.netnsok = true,
};
int nl80211_init(void)
{
int err;
err = genl_register_family_with_ops(&nl80211_fam,
nl80211_ops, ARRAY_SIZE(nl80211_ops));
。。。。
}
可以看到，linux无线网络驱动中已经注册了内核中的nl80211操作接口，名字为”nl80211″，那么当初始化用户态接口时，就可以通过名字来定位到内核中的接口了。
下面简单的分析命令的解析和处理，首先看下iw命令是怎么被注册的，
查看iw.h代码，
/* iw command 命令结构体 */
struct cmd {
const char *name;
const char *args;
const char *help;
const enum nl80211_commands cmd;
int nl_msg_flags;
int hidden;
const enum command_identify_by idby;
/*
* The handler should return a negative error code,
* zero on success, 1 if the arguments were wrong
* and the usage message should and 2 otherwise.
*/
int (*handler)(struct nl80211_state *state,
struct nl_msg *msg,
int argc, char **argv,
enum id_input id);
const struct cmd *(*selector)(int argc, char **argv);
const struct cmd *parent;
};
#define ARRAY_SIZE(ar) (sizeof(ar)/sizeof(ar[0]))
#define DIV_ROUND_UP(x, y) (((x) + (y - 1)) / (y))
/* 下面的几种宏初始化了cmd结构体变量 */
#define __COMMAND(_section, _symname, _name, _args, _nlcmd, _flags, _hidden, _idby, _handler, _help, _sel)\
static struct cmd \
__cmd ## _ ## _symname ## _ ## _handler ## _ ## _nlcmd ## _ ## _idby ## _ ## _hidden\
__attribute__((used)) __attribute__((section("__cmd"))) = { \
.name = (_name), \
.args = (_args), \
.cmd = (_nlcmd), \
.nl_msg_flags = (_flags), \
.hidden = (_hidden), \
.idby = (_idby), \
.handler = (_handler), \
.help = (_help), \
.parent = _section, \
.selector = (_sel), \
}
#define __ACMD(_section, _symname, _name, _args, _nlcmd, _flags, _hidden, _idby, _handler, _help, _sel, _alias)\
__COMMAND(_section, _symname, _name, _args, _nlcmd, _flags, _hidden, _idby, _handler, _help, _sel);\
static const struct cmd *_alias = &__cmd ## _ ## _symname ## _ ## _handler ## _ ## _nlcmd ## _ ## _idby ## _ ## _hidden
#define COMMAND(section, name, args, cmd, flags, idby, handler, help) \
__COMMAND(&(__section ## _ ## section), name, #name, args, cmd, flags, 0, idby, handler, help, NULL)
#define COMMAND_ALIAS(section, name, args, cmd, flags, idby, handler, help, selector, alias)\
__ACMD(&(__section ## _ ## section), name, #name, args, cmd, flags, 0, idby, handler, help, selector, alias)
#define HIDDEN(section, name, args, cmd, flags, idby, handler) \
__COMMAND(&(__section ## _ ## section), name, #name, args, cmd, flags, 1, idby, handler, NULL, NULL)
/* 定义了顶层命令 */
#define TOPLEVEL(_name, _args, _nlcmd, _flags, _idby, _handler, _help) \
struct cmd \
__section ## _ ## _name \
__attribute__((used)) __attribute__((section("__cmd"))) = { \
.name = (#_name), \
.args = (_args), \
.cmd = (_nlcmd), \
.nl_msg_flags = (_flags), \
.idby = (_idby), \
.handler = (_handler), \
.help = (_help), \
}
#define SECTION(_name) \
struct cmd __section ## _ ## _name \
__attribute__((used)) __attribute__((section("__cmd"))) = { \
.name = (#_name), \
.hidden = 1, \
}
#define DECLARE_SECTION(_name) \
extern struct cmd __section ## _ ## _name;
extern const char iw_version[];
extern int iw_debug;
int handle_cmd(struct nl80211_state *state, enum id_input idby,
int argc, char **argv);
。。。。。
。。。。。
DECLARE_SECTION(set);
DECLARE_SECTION(get);
(以下分析可能有错误！！)通过.h中的宏可以看到，iw定义了__cmd段，并将各种命令响应定义到了该段中，由于作者没有使用Linux，这里就懒一下，不在分析section中的排布和宏的解析了。不过需要注意的是iw的命令是树形结构的，分为两层，因此很多命令是有父命令的。这里随便举个例子吧,在interface.c中，
。。。。。 SECTION(interface); 。。。。。 COMMAND(interface, add, "<name> type <type> [mesh_id <meshid>] [4addr on|off] [flags <flag>*] [addr <mac-addr>]", NL80211_CMD_NEW_INTERFACE, 0, CIB_PHY, handle_interface_add, "Add a new virtual interface with the given configuration.\n" IFACE_TYPES "\n\n" "The flags are only used for monitor interfaces, valid flags are:\n" VALID_FLAGS "\n\n" "The mesh_id is used only for mesh mode."); COMMAND(interface, add, "<name> type <type> [mesh_id <meshid>] [4addr on|off] [flags <flag>*] [addr <mac-addr>]", NL80211_CMD_NEW_INTERFACE, 0, CIB_NETDEV, handle_interface_add, NULL);
.
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