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Diffstat (limited to 'Documentation/filesystems/sysfs.rst')
| -rw-r--r-- | Documentation/filesystems/sysfs.rst | 60 |
1 files changed, 32 insertions, 28 deletions
diff --git a/Documentation/filesystems/sysfs.rst b/Documentation/filesystems/sysfs.rst index 290891c3fecb..c32993bc83c7 100644 --- a/Documentation/filesystems/sysfs.rst +++ b/Documentation/filesystems/sysfs.rst @@ -12,15 +12,15 @@ Mike Murphy <mamurph@cs.clemson.edu> :Original: 10 January 2003 -What it is: -~~~~~~~~~~~ +What it is +~~~~~~~~~~ -sysfs is a ram-based filesystem initially based on ramfs. It provides +sysfs is a RAM-based filesystem initially based on ramfs. It provides a means to export kernel data structures, their attributes, and the linkages between them to userspace. sysfs is tied inherently to the kobject infrastructure. Please read -Documentation/kobject.txt for more information concerning the kobject +Documentation/core-api/kobject.rst for more information concerning the kobject interface. @@ -43,7 +43,7 @@ userspace. Top-level directories in sysfs represent the common ancestors of object hierarchies; i.e. the subsystems the objects belong to. -Sysfs internally stores a pointer to the kobject that implements a +sysfs internally stores a pointer to the kobject that implements a directory in the kernfs_node 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. @@ -55,7 +55,7 @@ Attributes ~~~~~~~~~~ Attributes can be exported for kobjects in the form of regular files in -the filesystem. Sysfs forwards file I/O operations to methods defined +the filesystem. sysfs forwards file I/O operations to methods defined for the attributes, providing a means to read and write kernel attributes. @@ -72,8 +72,8 @@ you publicly humiliated and your code rewritten without notice. An attribute definition is simply:: struct attribute { - char * name; - struct module *owner; + char *name; + struct module *owner; umode_t mode; }; @@ -138,7 +138,7 @@ __ATTR_WO(name): assumes a name_store only and is restricted to mode 0200 that is root write access only. __ATTR_RO_MODE(name, mode): - fore more restrictive RO access currently + for more restrictive RO access; currently only use case is the EFI System Resource Table (see drivers/firmware/efi/esrt.c) __ATTR_RW(name): @@ -172,14 +172,13 @@ 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) 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); + struct device *dev = kobj_to_dev(kobj); ssize_t ret = -EIO; if (dev_attr->show) @@ -208,7 +207,7 @@ IOW, they should take only an object, an attribute, and a buffer as parameters. sysfs allocates a buffer of size (PAGE_SIZE) and passes it to the -method. Sysfs will call the method exactly once for each read or +method. sysfs will call the method exactly once for each read or write. This forces the following behavior on the method implementations: @@ -222,7 +221,7 @@ implementations: be called again, rearmed, to fill the buffer. - On write(2), sysfs expects the entire buffer to be passed during the - first write. Sysfs then passes the entire buffer to the store() method. + first write. sysfs then passes the entire buffer to the store() method. A terminating null is added after the data on stores. This makes functions like sysfs_streq() safe to use. @@ -238,16 +237,14 @@ Other notes: - Writing causes the show() method to be rearmed regardless of current file position. -- The buffer will always be PAGE_SIZE bytes in length. On i386, this +- The buffer will always be PAGE_SIZE bytes in length. On x86, this is 4096. - show() methods should return the number of bytes printed into the - buffer. This is the return value of scnprintf(). + buffer. -- show() must not use snprintf() when formatting the value to be - returned to user space. If you can guarantee that an overflow - will never happen you can use sprintf() otherwise you must use - scnprintf(). +- show() should only use sysfs_emit() or sysfs_emit_at() when formatting + the value to be returned to user space. - store() should return the number of bytes used from the buffer. If the entire buffer has been used, just return the count argument. @@ -256,7 +253,7 @@ Other notes: through, be sure to return an error. - The object passed to the methods will be pinned in memory via sysfs - referencing counting its embedded object. However, the physical + reference counting its embedded object. However, the physical entity (e.g. device) the object represents may not be present. Be sure to have a way to check this, if necessary. @@ -266,7 +263,7 @@ 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) { - return scnprintf(buf, PAGE_SIZE, "%s\n", dev->name); + return sysfs_emit(buf, "%s\n", dev->name); } static ssize_t store_name(struct device *dev, struct device_attribute *attr, @@ -298,8 +295,12 @@ The top level sysfs directory looks like:: dev/ devices/ firmware/ - net/ fs/ + hypervisor/ + kernel/ + module/ + net/ + power/ devices/ contains a filesystem representation of the device tree. It maps directly to the internal kernel device tree, which is a hierarchy of @@ -320,15 +321,18 @@ span multiple bus types). fs/ contains a directory for some filesystems. Currently each filesystem wanting to export attributes must create its own hierarchy -below fs/ (see ./fuse.txt for an example). +below fs/ (see ./fuse.rst for an example). + +module/ contains parameter values and state information for all +loaded system modules, for both builtin and loadable modules. -dev/ contains two directories char/ and block/. Inside these two +dev/ contains two directories: char/ and block/. Inside these two directories there are symlinks named <major>:<minor>. These symlinks point to the sysfs directory for the given device. /sys/dev provides a quick way to lookup the sysfs interface for a device from the result of a stat(2) operation. -More information can driver-model specific features can be found in +More information on driver-model specific features can be found in Documentation/driver-api/driver-model/. @@ -338,7 +342,7 @@ TODO: Finish this section. Current Interfaces ~~~~~~~~~~~~~~~~~~ -The following interface layers currently exist in sysfs: +The following interface layers currently exist in sysfs. devices (include/linux/device.h) @@ -369,8 +373,8 @@ Structure:: struct bus_attribute { struct attribute attr; - ssize_t (*show)(struct bus_type *, char * buf); - ssize_t (*store)(struct bus_type *, const char * buf, size_t count); + ssize_t (*show)(const struct bus_type *, char * buf); + ssize_t (*store)(const struct bus_type *, const char * buf, size_t count); }; Declaring:: |