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Commit 30a69000 authored by Bart Van Assche's avatar Bart Van Assche Committed by Greg Kroah-Hartman
Browse files

sysfs: fix discrepancies between implementation and documentation 



Fix all discrepancies I know of between the sysfs implementation and its
documentation.

Signed-off-by: default avatarBart Van Assche <bart.vanassche@gmail.com>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent e3ed249a

Documentation/filesystems/sysfs.txt

+25 −19
Original line number Diff line number Diff line
@@ -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:    10 July 2010

Original:   10 January 2003
@@ -124,7 +124,7 @@ 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
@@ -139,18 +139,22 @@ 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;

        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;

}
@@ -163,10 +167,9 @@ 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 (*show)(struct device *dev, struct device_attribute *attr, char *buf);

ssize_t (*store)(struct device *dev, struct device_attribute *attr,

                 const char * buf);

                 const char *buf, size_t count);



IOW, they should take only an object, an attribute, and a buffer as parameters.
@@ -209,8 +212,8 @@ Other notes: 


- show() should always use snprintf(). 



- 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.
@@ -223,15 +226,18 @@ 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);

}



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);