如何将文件操作附加到平台驱动程序中的 sysfs 属性? [英] How to attach file operations to sysfs attribute in platform driver?

问题描述

我为我们开发的外围设备编写了一个平台驱动程序，并希望向 sysfs 公开一些配置选项.我已经设法在探测函数中使用属性结构(见下文)和 sysfs_create_file 创建了适当的文件，但我不知道如何将显示/存储函数附加到平台中的结构司机.

I wrote a platform driver for a peripheral we developed and would like to expose some configuration options to the sysfs. I have managed to create the appropriate files using attribute structs (see below) and sysfs_create_file in the probe function, but I can't figure out how to attach the show/store functions to the structs in a platform driver.

我在网上找到的大多数资源都使用 device_attribute 结构或类似的东西来创建它们的文件，这在这里也合适吗?对于平台驱动程序，还有其他方法可以做到这一点吗?

Most resources I found online used a device_attribute struct or something similar to create their files, is that also appropriate here? Is there another way to do this for a platform driver?

我的属性结构如下所示:

My attribute struct looks like this:

struct attribute subkey_attr = {
    .name = "subkeys",
    .mode = S_IWUGO | S_IRUGO,
};

我使用这个调用注册文件:

And I register the file using this call:

riddler_kobject = &pdev->dev.kobj;
ret_val = sysfs_create_file(riddler_kobject, &subkey_attr);

推荐答案

归结为下一个:

• 将 struct device(来自您的 struct platform_device)中的现有 kobject 重用于 sysfs_create_group()(而不是创建您自己的 kobject)
• 使用DEVICE_ATTR()来声明struct device_attribute而不是常规的__ATTR()，这会创建struct kobj_attribute.

• reuse existing kobject from struct device (from your struct platform_device) for sysfs_create_group() (instead of creating your own kobject)
• use DEVICE_ATTR() to declare struct device_attribute instead of regular __ATTR(), which creates struct kobj_attribute.

这是我为我的平台驱动程序创建 sysfs 属性的方法.

Here is how I created sysfs attributes for my platform driver.

1. 创建您将在 show()/store() 操作中用作 sysfs 属性(文件)的私有数据的结构.例如:

1. Create structure you'll be using as private data in show() / store() operations for your sysfs attribute (file). For example:

struct mydrv {
    struct device *dev;
    long myparam;
};

在驱动程序的probe()中分配这个结构:

static int mydrv_probe(struct platform_device *pdev)
{
    struct mydrv *mydrv;

    mydrv = devm_kzalloc(&pdev->dev, sizeof(*mydrv), GFP_KERNEL);
    mydrv->dev = &pdev->dev;
    platform_set_drvdata(pdev, mydrv);

    ...
}

创建show()/store() 函数:

static ssize_t mydrv_myparam_show(struct device *dev,
        struct device_attribute *attr, char *buf)
{
    struct mydrv *mydrv = dev_get_drvdata(dev);
    int len;

    len = sprintf(buf, "%d
", mydrv->myparam);
    if (len <= 0)
        dev_err(dev, "mydrv: Invalid sprintf len: %d
", len);

    return len;
}

static ssize_t mydrv_myparam_store(struct device *dev,
        struct device_attribute *attr, const char *buf, size_t count)
{
    struct mydrv *mydrv = dev_get_drvdata(dev);

    kstrtol(buf, 10, &mydrv->myparam);
    return count;
}

为这些函数创建设备属性(在这些函数之后):

Create device attribute for those functions (right after those functions):

static DEVICE_ATTR(myparam, S_IRUGO | S_IWUSR, mydrv_myparam_show,
                   mydrv_myparam_store);

声明属性表(实际上为您的驱动程序列出sysfs 文件):

static struct attribute *mydrv_attrs[] = {
    &dev_attr_myparam.attr,
    NULL
};

声明属性组(实际上为您的驱动程序指定sysfs目录):

static struct attribute_group mydrv_group = {
    .name = "mydrv",
    .attrs = mydrv_attrs,
};

static struct attribute_group *mydrv_groups[] = {
    &mydrv_group,
    NULL
}

实际上可以用一行替换:

which can be actually replaced with one line:

ATTRIBUTE_GROUPS(mydrv);

在驱动程序的 probe() 函数中创建 sysfs 目录和文件:

Create sysfs directory and files in your driver's probe() function:

static int mydrv_probe(struct platform_device *pdev)
{
    int ret;

    ...

    ret = sysfs_create_group(&pdev->dev.kobj, &mydrv_group);
    if (ret) {
        dev_err(&pdev->dev, "sysfs creation failed
");
        return ret;
    }

    ...
}

在驱动程序的 remove() 函数中删除 sysfs 文件:

Remove your sysfs files in your driver's remove() function:

static int mydrv_remove(struct platform_device *pdev)
{
    sysfs_remove_group(&pdev->dev.kobj, &mydrv_group);
    ...
}

比赛条件说明

正如@FranzForstmayr 正确指出的那样，在mydrv_probe() 中使用sysfs_create_group() 添加sysfs 文件时可能会出现竞争条件.这是因为用户空间可以在 mydrv_probe() 调用之前已经通知这些文件存在(这些文件实际上是由 sysfs_create_group() 函数创建的).中详细介绍了此问题如何正确创建 sysfs 文件" Greg Kroah-Hartman 的文章.

Race condition note

As @FranzForstmayr correctly pointed out, there may be race condition when adding sysfs files with sysfs_create_group() in mydrv_probe(). That's because user-space can be already notified that those files exist before mydrv_probe() called (where those files are actually being created by sysfs_create_group() function). This issue covered in details in "How to Create a sysfs File Correctly" article by Greg Kroah-Hartman.

因此，在我们的 platform_device 示例中，您可以使用 sysfs_create_group()(及其对应的 sysfs_remove_group())，而不是调用 强>默认属性组.为此，您需要将 struct device 的相应 .groups 字段分配给您的属性组变量:

So in our case of platform_device, instead of calling sysfs_create_group() (and its counterpart sysfs_remove_group()), you can use default attribute group. To do so, you need to assign corresponding .groups field of your struct device to your attribute groups variable:

static int mydrv_probe(struct platform_device *pdev)
{
    ...

    pdev->dev.groups = mydrv_groups;

    ...
}

免责声明:我没有测试这段代码，虽然它应该可以工作，因为 这个代码.

DISCLAIMER: I didn't test this code, though it should work, because of this code.

请参阅 [1,2,3] 链接以获取有关上述竞争条件的更多见解.

See [1,2,3] links for more insights on mentioned race condition.

更多示例，请在内核源目录中运行下一个命令:

For more examples, run next command in kernel source directory:

$ git grep -l --all-match -e platform_device -e attribute -e '.groups =' -- drivers/

您也可以在提交消息中通过默认属性"进行搜索:

Also you can search by "default attribute" in commit messages:

$ git log --no-merges --oneline --grep="default attribute" -- drivers/

我通过这种方式发现的一些提交:[4,5,6,7].

Some commits I found this way: [4,5,6,7].

[1] 我的属性太活泼了，我该怎么办?

[2] PATCH:sysfs:添加 devm_sysfs_create_group() 和朋友

[3] [GIT PATCH] 3.11-rc2 驱动核心补丁

[4] 提交 1

[5] 提交 2

[6] 提交 3

[7] 提交 4

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