sysfs Attributes

Expose device properties through /sys/.

DEVICE_ATTR

Create read/write attributes for your device:

/* Read-only attribute */
static ssize_t status_show(struct device *dev,
                           struct device_attribute *attr, char *buf)
{
    struct my_dev *mydev = dev_get_drvdata(dev);
    return sysfs_emit(buf, "%d\n", mydev->status);
}
static DEVICE_ATTR_RO(status);

/* Read-write attribute */
static ssize_t config_show(struct device *dev,
                           struct device_attribute *attr, char *buf)
{
    struct my_dev *mydev = dev_get_drvdata(dev);
    return sysfs_emit(buf, "%u\n", mydev->config);
}

static ssize_t config_store(struct device *dev,
                            struct device_attribute *attr,
                            const char *buf, size_t count)
{
    struct my_dev *mydev = dev_get_drvdata(dev);
    unsigned int val;

    if (kstrtouint(buf, 0, &val))
        return -EINVAL;

    mydev->config = val;
    return count;
}
static DEVICE_ATTR_RW(config);

Attribute Groups

Group attributes together (preferred method):

static struct attribute *my_attrs[] = {
    &dev_attr_status.attr,
    &dev_attr_config.attr,
    NULL,
};
ATTRIBUTE_GROUPS(my);

/* In driver */
static struct platform_driver my_driver = {
    .driver = {
        .name = "my_driver",
        .dev_groups = my_groups,  /* Auto-created on probe */
    },
};

Use dev_groups in driver struct. Attributes are automatically created during probe and removed during remove.

Using sysfs_emit

Always use sysfs_emit() instead of sprintf():

/* Good */
return sysfs_emit(buf, "%d\n", value);

/* Bad - may overflow */
return sprintf(buf, "%d\n", value);

Binary Attributes

For binary data (firmware dumps, etc.):

static ssize_t data_read(struct file *filp, struct kobject *kobj,
                         struct bin_attribute *attr,
                         char *buf, loff_t off, size_t count)
{
    struct device *dev = kobj_to_dev(kobj);
    struct my_dev *mydev = dev_get_drvdata(dev);

    return memory_read_from_buffer(buf, count, &off,
                                   mydev->data, mydev->data_size);
}
static BIN_ATTR_RO(data, DATA_SIZE);

Summary

Macro	Creates
DEVICE_ATTR_RO(name)	Read-only attribute
DEVICE_ATTR_WO(name)	Write-only attribute
DEVICE_ATTR_RW(name)	Read-write attribute
ATTRIBUTE_GROUPS(name)	Attribute group

Further Reading

• sysfs Documentation
• Device Attributes