使用 Linux sysfs_notify 调用 [英] Using the Linux sysfs_notify call
问题描述
我正在尝试在内核驱动程序和用户空间程序之间进行异步通信(我知道这里有很多问题需要类似的信息，但我找不到与 sysfs_notify 相关的问题).
I am trying to communicate asynchronously between a kernel driver and a user-space program (I know there are lots of questions here that ask for similar information, but I could find none that deal with sysfs_notify).
我将 Vilhelm 的编辑留在这里，但是将源添加到一个使用 sysfs 的简单驱动程序和一个用户空间程序来轮询它.驱动程序工作正常(我从网上获得了大部分内容；它缺少信用，但当我回去添加它们时找不到它们).不幸的是，轮询程序不起作用.它总是立即返回成功.有趣的是，如果我在轮询之前不执行两次读取，则 revents 成员将设置为 POLLERR |POLLIN 而不仅仅是程序输出中的 POLLIN.
I am leaving Vilhelm's edit here, but adding the source to both a simple driver utilizing sysfs and a user-space program to poll it. The driver works fine (I got most of it from the net; it is missing the credits, but I couldn't find them when I went back to add them). Unfortunately, the polling program does not work. It always returns success immediately. Interestingly, if I don't perform the two reads prior to the poll, the revents members are set to POLLERR | POLLIN instead of just POLLIN as seen in the program output.
程序输出:
root@ubuntu:/home/wmulcahy/demo# ./readhello
触发
属性文件值:74 (t) [0]
revents[0]: 00000001
revents[1]: 00000001
root@ubuntu:/home/wmulcahy/demo# ./readhello
triggered
Attribute file value: 74 (t) [0]
revents[0]: 00000001
revents[1]: 00000001
这是驱动程序:hello.c(你可以看到我从哪里开始......)
Here is the driver: hello.c (you can see where I started out...)
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/slab.h>
struct my_attr {
struct attribute attr;
int value;
};
static struct my_attr notify = {
.attr.name="notify",
.attr.mode = 0644,
.value = 0,
};
static struct my_attr trigger = {
.attr.name="trigger",
.attr.mode = 0644,
.value = 0,
};
static struct attribute * myattr[] = {
¬ify.attr,
&trigger.attr,
NULL
};
static ssize_t show(struct kobject *kobj, struct attribute *attr, char *buf)
{
struct my_attr *a = container_of(attr, struct my_attr, attr);
printk( "hello: show called (%s)
", a->attr.name );
return scnprintf(buf, PAGE_SIZE, "%s: %d
", a->attr.name, a->value);
}
static struct kobject *mykobj;
static ssize_t store(struct kobject *kobj, struct attribute *attr, const char *buf, size_t len)
{
struct my_attr *a = container_of(attr, struct my_attr, attr);
sscanf(buf, "%d", &a->value);
notify.value = a->value;
printk("sysfs_notify store %s = %d
", a->attr.name, a->value);
sysfs_notify(mykobj, NULL, "notify");
return sizeof(int);
}
static struct sysfs_ops myops = {
.show = show,
.store = store,
};
static struct kobj_type mytype = {
.sysfs_ops = &myops,
.default_attrs = myattr,
};
static struct kobject *mykobj;
static int __init hello_module_init(void)
{
int err = -1;
printk("Hello: init
");
mykobj = kzalloc(sizeof(*mykobj), GFP_KERNEL);
if (mykobj) {
kobject_init(mykobj, &mytype);
if (kobject_add(mykobj, NULL, "%s", "hello")) {
err = -1;
printk("Hello: kobject_add() failed
");
kobject_put(mykobj);
mykobj = NULL;
}
err = 0;
}
return err;
}
static void __exit hello_module_exit(void)
{
if (mykobj) {
kobject_put(mykobj);
kfree(mykobj);
}
printk("Hello: exit
");
}
module_init(hello_module_init);
module_exit(hello_module_exit);
MODULE_LICENSE("GPL");
这里是轮询程序:readhello.c
And here is the poll program: readhello.c
#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <poll.h>
#define TEST_SYSFS_TRIGGER "/sys/hello/trigger"
#define TEST_SYSFS_NOTIFY "/sys/hello/notify"
int main(int argc, char **argv)
{
int cnt, notifyFd, triggerFd, rv;
char attrData[100];
struct pollfd ufds[2];
// Open a connection to the attribute file.
if ((notifyFd = open(TEST_SYSFS_NOTIFY, O_RDWR)) < 0)
{
perror("Unable to open notify");
exit(1);
}
// Open a connection to the attribute file.
if ((triggerFd = open(TEST_SYSFS_TRIGGER, O_RDWR)) < 0)
{
perror("Unable to open trigger");
exit(1);
}
ufds[0].fd = notifyFd;
ufds[0].events = POLLIN;
ufds[1].fd = triggerFd;
ufds[1].events = POLLIN;
// Someone suggested dummy reads before the poll() call
cnt = read( notifyFd, attrData, 100 );
cnt = read( triggerFd, attrData, 100 );
ufds[0].revents = 0;
ufds[1].revents = 0;
if (( rv = poll( ufds, 2, 10000)) < 0 )
{
perror("poll error");
}
else if (rv == 0)
{
printf("Timeout occurred!
");
}
else if (ufds[0].revents & POLLIN)
{
printf("triggered
");
cnt = read( notifyFd, attrData, 1 );
printf( "Attribute file value: %02X (%c) [%d]
", attrData[0], attrData[0], cnt );
}
printf( "revents[0]: %08X
", ufds[0].revents );
printf( "revents[1]: %08X
", ufds[1].revents );
close( triggerFd );
close( notifyFd );
}
在内部，补丁为每个 kobject 添加了一个等待队列头系统;该队列被插入到轮询表中以响应轮询()调用.sysfs 代码无法知道，但是，当任何给定 sysfs 属性的值已更改，因此子系统实现可轮询属性必须显式调用:
Internally, the patch adds a wait queue head to every kobject on the system; that queue is inserted into a poll table in response to a poll() call. The sysfs code has no way of knowing, however, when the value of any given sysfs attribute has changed, so the subsystem implementing a pollable attribute must make explicit calls to:
void sysfs_notify(struct kobject *kobj, char *dir, char *attr);
谢谢，李
推荐答案
阻塞轮询来自用户端.用户代码可以简单地告诉内核它对哪些属性感兴趣，然后阻塞在 poll() 中，直到其中一个发生更改.
The blocking poll is from the user side. User code can simply tell the kernel which attributes it's interested in, then block in a poll() until one of them has changed.
sysfs_notify() 是内核端调用，用于释放用户空间poll().调整内核属性值后，只需调用 sysfs_notify() 以允许任何用户空间应用程序响应其未完成的 poll().
The sysfs_notify() is a kernel-side call that releases the user-space poll(). After you adjust your kernel attribute value, just call sysfs_notify() to allow any user-space applications to respond to their outstanding poll().
将 poll() 视为订阅"感兴趣的属性更改的通知，而 sysfs_notify() 将更改视为发布"到任何订阅者.
Think of the poll() as "subscribing" to notices of a change in an attribute of interest, and sysfs_notify() as "publishing" the change to any subscribers.
这篇关于使用 Linux sysfs_notify 调用的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
