udev（九）-- 写个程序检测我们的设备插拔

原创文章，转载请注明出处，谢谢！

作者：清林，博客名：飞空静渡

在这个教程里我将写一个程序，其作用是检测系统的设备插拔事件，当有设备插入
系统时，就可以检测到这个设备并把设备的信息显示出来，如果设备从系统里移除，也同样可以检测出来，并移除设备。这个代码是参考了udev-139的源码
的，如果读者有兴趣也可以参考udev的源码。其中在udev-139代码中有个小小的错误，我将在下面的代码中说出。

首先先说一下udev的一个命令，你可以在控制台下运行：

udevadm monitor

我的运行如下图所示：



当插入我的金士顿优盘时，便可以检测到优盘的插入，如下图：



我们现在要做就是写个程序，其输出和上面的一样，其实也就是udevadm的
源码，我只是把它的大部分代码移除，只留个检测插拔事件的代码，并把很多地方的宏和函数集成到一个文件中。其中具体代码的API可参考libudev
Reference
Manual的说明：http://www.kernel.org/pub/linux/utils/kernel/hotplug/libudev
/ch01.html

下面是源代码udevadm.c：

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#include <unistd.h>


#include <stdio.h>


#include <stdlib.h>


#include <stddef.h>


#include <string.h>


#include <errno.h>


#include <getopt.h>


#include <fcntl.h>


#include <errno.h>


#include <signal.h>


#include <getopt.h>


#include <sys/time.h>


#include <sys/socket.h>


#include <sys/un.h>


#include <sys/select.h>


#include <linux/types.h>


#include <linux/netlink.h>


#undef asmlinkage


#ifdef __i386__


#define asmlinkage __attribute__((regparm(0)))


#else


#define asmlinkage


#endif


#define UDEV_MAX(a,b) ((a) > (b) ? (a) : (b))


#define udev_list_entry_foreach(entry, first) /


for
(entry = first; /

entry != NULL; /

entry = udev_list_entry_get_next(entry))

static

int
debug;

static

int
udev_exit;

static

void
asmlinkage sig_handler(
int
signum)

{

if
(signum == SIGINT || signum == SIGTERM)

udev_exit = 1;

}

static

void
print_device(
struct
udev_device *device,
const

char
*source,
int
env)

{

struct
timeval tv;

struct
timezone tz;

gettimeofday(&tv, &tz);

printf("%-6s[%llu.%06u] %-8s %s (%s)/n"
,

source,

(unsigned long

long
) tv.tv_sec, (unsigned
int
) tv.tv_usec,

udev_device_get_action(device),

udev_device_get_devpath(device),

udev_device_get_subsystem(device));

if
(env) {

struct
udev_list_entry *list_entry;

udev_list_entry_foreach(list_entry, udev_device_get_properties_list_entry(device))

printf("%s=%s/n"
,

udev_list_entry_get_name(list_entry),

udev_list_entry_get_value(list_entry));

printf("/n"
);

}

}

int
udevadm_monitor(
struct
udev *udev)

{

struct
sigaction act;

int
env = 0;

int
print_kernel = 0;

int
print_udev = 0;

struct
udev_monitor *udev_monitor = NULL;

struct
udev_monitor *kernel_monitor = NULL;

fd_set readfds;

int
rc = 0;

if
(!print_kernel && !print_udev) {

print_kernel = 1;

print_udev =1;

}

if
(getuid() != 0 && print_kernel) {

fprintf(stderr, "root privileges needed to subscribe to kernel events/n"
);

goto
out;

}

/* set signal handlers */


memset(&act, 0x00, sizeof
(
struct
sigaction));

act.sa_handler = (void
(*)(
int
)) sig_handler;

sigemptyset(&act.sa_mask);

act.sa_flags = SA_RESTART;

sigaction(SIGINT, &act, NULL);

sigaction(SIGTERM, &act, NULL);

printf("monitor will print the received events for:/n"
);

if
(print_udev) {

udev_monitor = udev_monitor_new_from_socket(udev, "@/org/kernel/udev/monitor"
);

if
(udev_monitor == NULL) {

rc = 1;

goto
out;

}

if
(udev_monitor_enable_receiving(udev_monitor) < 0) {

rc = 2;

goto
out;

}

printf("UDEV the event which udev sends out after rule processing/n"
);

}



if
(print_kernel) {

kernel_monitor = udev_monitor_new_from_netlink(udev, "udev"
);
//这里的udev源码中没有"udev"这个参数，不加进去返回值就为NULL，所以要加这个


if
(kernel_monitor == NULL) {

rc = 3;

printf("udev_monitor_new_from_netlink() error/n"
);

goto
out;

}

if
(udev_monitor_enable_receiving(kernel_monitor) < 0) {

rc = 4;

goto
out;

}

printf("UEVENT the kernel uevent/n"
);

}



printf("/n"
);

while
(!udev_exit) {

int
fdcount;

FD_ZERO(&readfds);

if
(kernel_monitor != NULL)

FD_SET(udev_monitor_get_fd(kernel_monitor), &readfds);

if
(udev_monitor != NULL)

FD_SET(udev_monitor_get_fd(udev_monitor), &readfds);

fdcount = select(UDEV_MAX(udev_monitor_get_fd(kernel_monitor), udev_monitor_get_fd(udev_monitor))+1,

&readfds, NULL, NULL, NULL);

if
(fdcount < 0) {

if
(errno != EINTR)

fprintf(stderr, "error receiving uevent message: %m/n"
);

continue
;

}

if
((kernel_monitor != NULL) && FD_ISSET(udev_monitor_get_fd(kernel_monitor), &readfds)) {

struct
udev_device *device;

device = udev_monitor_receive_device(kernel_monitor);

if
(device == NULL)

continue
;

print_device(device, "UEVENT"
, env);

udev_device_unref(device);

}

if
((udev_monitor != NULL) && FD_ISSET(udev_monitor_get_fd(udev_monitor), &readfds)) {

struct
udev_device *device;

device = udev_monitor_receive_device(udev_monitor);

if
(device == NULL)

continue
;

print_device(device, "UDEV"
, env);

udev_device_unref(device);

}

}

out:

udev_monitor_unref(udev_monitor);

udev_monitor_unref(kernel_monitor);

return
rc;

}

int
main(
int
argc,
char
*argv[])

{

struct
udev *udev;

int
rc = 1;

udev = udev_new();

if
(udev == NULL)

goto
out;

udevadm_monitor(udev);

goto
out;

rc = 2;

out:

udev_unref(udev);

return
rc;

}

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <stddef.h>
#include <string.h>
#include <errno.h>
#include <getopt.h>
#include <fcntl.h>
#include <errno.h>
#include <signal.h>
#include <getopt.h>
#include <sys/time.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/select.h>
#include <linux/types.h>
#include <linux/netlink.h>
#undef asmlinkage
#ifdef __i386__
#define asmlinkage __attribute__((regparm(0)))
#else
#define asmlinkage 
#endif
#define UDEV_MAX(a,b) ((a) > (b) ? (a) : (b))
#define udev_list_entry_foreach(entry, first) /
	for (entry = first; /
	     entry != NULL; /
	     entry = udev_list_entry_get_next(entry))
static int debug;
static int udev_exit;
static void asmlinkage sig_handler(int signum)
{
	if (signum == SIGINT || signum == SIGTERM)
		udev_exit = 1;
}
static void print_device(struct udev_device *device, const char *source, int env)
{
	struct timeval tv;
	struct timezone tz;
	gettimeofday(&tv, &tz);
	printf("%-6s[%llu.%06u] %-8s %s (%s)/n",
	       source,
	       (unsigned long long) tv.tv_sec, (unsigned int) tv.tv_usec,
	       udev_device_get_action(device),
	       udev_device_get_devpath(device),
	       udev_device_get_subsystem(device));
	if (env) {
		struct udev_list_entry *list_entry;
		udev_list_entry_foreach(list_entry, udev_device_get_properties_list_entry(device))
			printf("%s=%s/n",
			       udev_list_entry_get_name(list_entry),
			       udev_list_entry_get_value(list_entry));
		printf("/n");
	}
}
int udevadm_monitor(struct udev *udev)
{
	struct sigaction act;
	int env = 0;
	int print_kernel = 0;
	int print_udev = 0;
	struct udev_monitor *udev_monitor = NULL;
	struct udev_monitor *kernel_monitor = NULL;
	fd_set readfds;
	int rc = 0;
	if (!print_kernel && !print_udev) {
		print_kernel = 1;
		print_udev =1;
	}
	if (getuid() != 0 && print_kernel) {
		fprintf(stderr, "root privileges needed to subscribe to kernel events/n");
		goto out;
	}
	/* set signal handlers */
	memset(&act, 0x00, sizeof(struct sigaction));
	act.sa_handler = (void (*)(int)) sig_handler;
	sigemptyset(&act.sa_mask);
	act.sa_flags = SA_RESTART;
	sigaction(SIGINT, &act, NULL);
	sigaction(SIGTERM, &act, NULL);
	printf("monitor will print the received events for:/n");
	if (print_udev) {
		udev_monitor = udev_monitor_new_from_socket(udev, "@/org/kernel/udev/monitor");
		if (udev_monitor == NULL) {
			rc = 1;
			goto out;
		}
		if (udev_monitor_enable_receiving(udev_monitor) < 0) {
			rc = 2;
			goto out;
		}
		printf("UDEV the event which udev sends out after rule processing/n");
	}
	
	if (print_kernel) {
		kernel_monitor = udev_monitor_new_from_netlink(udev, "udev"); //这里的udev源码中没有"udev"这个参数，不加进去返回值就为NULL，所以要加这个
		if (kernel_monitor == NULL) {
			rc = 3;
			printf("udev_monitor_new_from_netlink() error/n");
			goto out;
		}
		if (udev_monitor_enable_receiving(kernel_monitor) < 0) {
			rc = 4;
			goto out;
		}
		printf("UEVENT the kernel uevent/n");
	}
	
	printf("/n");
	while (!udev_exit) {
		int fdcount;
		FD_ZERO(&readfds);
		if (kernel_monitor != NULL)
			FD_SET(udev_monitor_get_fd(kernel_monitor), &readfds);
		if (udev_monitor != NULL)
			FD_SET(udev_monitor_get_fd(udev_monitor), &readfds);
		fdcount = select(UDEV_MAX(udev_monitor_get_fd(kernel_monitor), udev_monitor_get_fd(udev_monitor))+1,
				 &readfds, NULL, NULL, NULL);
		if (fdcount < 0) {
			if (errno != EINTR)
				fprintf(stderr, "error receiving uevent message: %m/n");
			continue;
		}
		if ((kernel_monitor != NULL) && FD_ISSET(udev_monitor_get_fd(kernel_monitor), &readfds)) {
			struct udev_device *device;
			device = udev_monitor_receive_device(kernel_monitor);
			if (device == NULL)
				continue;
			print_device(device, "UEVENT", env);
			udev_device_unref(device);
		}
		if ((udev_monitor != NULL) && FD_ISSET(udev_monitor_get_fd(udev_monitor), &readfds)) {
			struct udev_device *device;
			device = udev_monitor_receive_device(udev_monitor);
			if (device == NULL)
				continue;
			print_device(device, "UDEV", env);
			udev_device_unref(device);
		}
	}
out:
	udev_monitor_unref(udev_monitor);
	udev_monitor_unref(kernel_monitor);
	return rc;
}
int main(int argc, char *argv[])
{
	struct udev *udev;
	int rc = 1;
	udev = udev_new();
	if (udev == NULL)
		goto out;
	udevadm_monitor(udev);
	goto out;
	rc = 2;
out:
	udev_unref(udev);
	return rc;
}

下面是Makefile

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myudevadm: udevadm.c

gcc -g -Wall -ludev udevadm.c -o myudevadm

myudevadm: udevadm.c
       gcc -g -Wall -ludev udevadm.c -o myudevadm

当插入和拔出优盘是的显示如下图：



记得加个sudo，要退出按ctrl-c，我的运行环境是ubuntu9.10。可看到我的优盘设备是sde，有关分区是sde4，这个你可以在/dev目录下找到，并且是usb设备。/

来源：http://blog.csdn.net/fjb2080/archive/2009/12/15/5009791.aspx