diff options
Diffstat (limited to 'Documentation/filesystems/sysfs.txt')
| -rw-r--r-- | Documentation/filesystems/sysfs.txt | 95 |
1 files changed, 56 insertions, 39 deletions
diff --git a/Documentation/filesystems/sysfs.txt b/Documentation/filesystems/sysfs.txt index 7e81e37c0b1..b35a64b82f9 100644 --- a/Documentation/filesystems/sysfs.txt +++ b/Documentation/filesystems/sysfs.txt @@ -4,7 +4,7 @@ sysfs - _The_ filesystem for exporting kernel objects. Patrick Mochel <mochel@osdl.org> Mike Murphy <mamurph@cs.clemson.edu> -Revised: 22 February 2009 +Revised: 16 August 2011 Original: 10 January 2003 @@ -23,7 +23,8 @@ interface. Using sysfs ~~~~~~~~~~~ -sysfs is always compiled in. You can access it by doing: +sysfs is always compiled in if CONFIG_SYSFS is defined. You can access +it by doing: mount -t sysfs sysfs /sys @@ -38,10 +39,12 @@ userspace. Top-level directories in sysfs represent the common ancestors of object hierarchies; i.e. the subsystems the objects belong to. -Sysfs internally stores the kobject that owns the directory in the -->d_fsdata pointer of the directory's dentry. This allows sysfs to do -reference counting directly on the kobject when the file is opened and -closed. +Sysfs internally stores a pointer to the kobject that implements a +directory in the sysfs_dirent object associated with the directory. In +the past this kobject pointer has been used by sysfs to do reference +counting directly on the kobject whenever the file is opened or closed. +With the current sysfs implementation the kobject reference count is +only modified directly by the function sysfs_schedule_callback(). Attributes @@ -59,7 +62,7 @@ values of the same type. Mixing types, expressing multiple lines of data, and doing fancy formatting of data is heavily frowned upon. Doing these things may get -you publically humiliated and your code rewritten without notice. +you publicly humiliated and your code rewritten without notice. An attribute definition is simply: @@ -67,7 +70,7 @@ An attribute definition is simply: struct attribute { char * name; struct module *owner; - mode_t mode; + umode_t mode; }; @@ -90,8 +93,8 @@ struct device_attribute { const char *buf, size_t count); }; -int device_create_file(struct device *, struct device_attribute *); -void device_remove_file(struct device *, struct device_attribute *); +int device_create_file(struct device *, const struct device_attribute *); +void device_remove_file(struct device *, const struct device_attribute *); It also defines this helper for defining device attributes: @@ -105,12 +108,12 @@ static DEVICE_ATTR(foo, S_IWUSR | S_IRUGO, show_foo, store_foo); is equivalent to doing: static struct device_attribute dev_attr_foo = { - .attr = { + .attr = { .name = "foo", .mode = S_IWUSR | S_IRUGO, - .show = show_foo, - .store = store_foo, }, + .show = show_foo, + .store = store_foo, }; @@ -123,7 +126,7 @@ show and store methods of the attribute owners. struct sysfs_ops { ssize_t (*show)(struct kobject *, struct attribute *, char *); - ssize_t (*store)(struct kobject *, struct attribute *, const char *); + ssize_t (*store)(struct kobject *, struct attribute *, const char *, size_t); }; [ Subsystems should have already defined a struct kobj_type as a @@ -138,18 +141,22 @@ calls the associated methods. To illustrate: +#define to_dev(obj) container_of(obj, struct device, kobj) #define to_dev_attr(_attr) container_of(_attr, struct device_attribute, attr) -#define to_dev(d) container_of(d, struct device, kobj) -static ssize_t -dev_attr_show(struct kobject * kobj, struct attribute * attr, char * buf) +static ssize_t dev_attr_show(struct kobject *kobj, struct attribute *attr, + char *buf) { - struct device_attribute * dev_attr = to_dev_attr(attr); - struct device * dev = to_dev(kobj); - ssize_t ret = 0; + struct device_attribute *dev_attr = to_dev_attr(attr); + struct device *dev = to_dev(kobj); + ssize_t ret = -EIO; if (dev_attr->show) - ret = dev_attr->show(dev, buf); + ret = dev_attr->show(dev, dev_attr, buf); + if (ret >= (ssize_t)PAGE_SIZE) { + print_symbol("dev_attr_show: %s returned bad count\n", + (unsigned long)dev_attr->show); + } return ret; } @@ -162,10 +169,9 @@ To read or write attributes, show() or store() methods must be specified when declaring the attribute. The method types should be as simple as those defined for device attributes: -ssize_t (*show)(struct device * dev, struct device_attribute * attr, - char * buf); -ssize_t (*store)(struct device * dev, struct device_attribute * attr, - const char * buf); +ssize_t (*show)(struct device *dev, struct device_attribute *attr, char *buf); +ssize_t (*store)(struct device *dev, struct device_attribute *attr, + const char *buf, size_t count); IOW, they should take only an object, an attribute, and a buffer as parameters. @@ -204,12 +210,12 @@ Other notes: is 4096. - show() methods should return the number of bytes printed into the - buffer. This is the return value of snprintf(). + buffer. This is the return value of scnprintf(). -- show() should always use snprintf(). +- show() should always use scnprintf(). -- store() should return the number of bytes used from the buffer. This - can be done using strlen(). +- store() should return the number of bytes used from the buffer. If the + entire buffer has been used, just return the count argument. - show() or store() can always return errors. If a bad value comes through, be sure to return an error. @@ -222,15 +228,18 @@ Other notes: A very simple (and naive) implementation of a device attribute is: -static ssize_t show_name(struct device *dev, struct device_attribute *attr, char *buf) +static ssize_t show_name(struct device *dev, struct device_attribute *attr, + char *buf) { - return snprintf(buf, PAGE_SIZE, "%s\n", dev->name); + return scnprintf(buf, PAGE_SIZE, "%s\n", dev->name); } -static ssize_t store_name(struct device * dev, const char * buf) +static ssize_t store_name(struct device *dev, struct device_attribute *attr, + const char *buf, size_t count) { - sscanf(buf, "%20s", dev->name); - return strnlen(buf, PAGE_SIZE); + snprintf(dev->name, sizeof(dev->name), "%.*s", + (int)min(count, sizeof(dev->name) - 1), buf); + return count; } static DEVICE_ATTR(name, S_IRUGO, show_name, store_name); @@ -315,8 +324,8 @@ DEVICE_ATTR(_name, _mode, _show, _store); Creation/Removal: -int device_create_file(struct device *device, struct device_attribute * attr); -void device_remove_file(struct device * dev, struct device_attribute * attr); +int device_create_file(struct device *dev, const struct device_attribute * attr); +void device_remove_file(struct device *dev, const struct device_attribute * attr); - bus drivers (include/linux/device.h) @@ -326,7 +335,7 @@ Structure: struct bus_attribute { struct attribute attr; ssize_t (*show)(struct bus_type *, char * buf); - ssize_t (*store)(struct bus_type *, const char * buf); + ssize_t (*store)(struct bus_type *, const char * buf, size_t count); }; Declaring: @@ -357,7 +366,15 @@ DRIVER_ATTR(_name, _mode, _show, _store) Creation/Removal: -int driver_create_file(struct device_driver *, struct driver_attribute *); -void driver_remove_file(struct device_driver *, struct driver_attribute *); +int driver_create_file(struct device_driver *, const struct driver_attribute *); +void driver_remove_file(struct device_driver *, const struct driver_attribute *); +Documentation +~~~~~~~~~~~~~ + +The sysfs directory structure and the attributes in each directory define an +ABI between the kernel and user space. As for any ABI, it is important that +this ABI is stable and properly documented. All new sysfs attributes must be +documented in Documentation/ABI. See also Documentation/ABI/README for more +information. |