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Subject[PATCH 16/28] sysfs: fix discrepancies between implementation and documentation
Date
From: Bart Van Assche <bvanassche@acm.org>

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>
---
Documentation/filesystems/sysfs.txt | 44 +++++++++++++++++++---------------
1 files changed, 25 insertions(+), 19 deletions(-)

diff --git a/Documentation/filesystems/sysfs.txt b/Documentation/filesystems/sysfs.txt
index 931c806..d78ed0b 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: 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);
--
1.7.2


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