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sysfs: fix discrepancies between implementation and documentation 

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

Signed-off-by: Bart Van Assche <bart.vanassche@gmail.com>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Bart Van Assche 2010-07-20 15:22:05 -07:00 committed by Greg Kroah-Hartman
parent e3ed249af8
commit 30a69000a4
1 changed files with 25 additions and 19 deletions
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44
Documentation/filesystems/sysfs.txt
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@ -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;
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;
}
@ -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 (*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.
@ -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);