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author | Bart Van Assche <bvanassche@acm.org> | 2010-07-20 15:22:05 -0700 |
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committer | Greg Kroah-Hartman <gregkh@suse.de> | 2010-08-05 13:53:34 -0700 |
commit | 30a69000a4ba9cf49e8b826431847cc80881b59b (patch) | |
tree | a0fe01bb1f5256046c4ab86d75bc6777fa821bc5 /Documentation | |
parent | e3ed249af8cb2f73fc6ef5494d2ddef43fb0ff19 (diff) | |
download | lwn-30a69000a4ba9cf49e8b826431847cc80881b59b.tar.gz lwn-30a69000a4ba9cf49e8b826431847cc80881b59b.zip |
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>
Diffstat (limited to 'Documentation')
-rw-r--r-- | 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 931c806642c5..d78ed0bb2756 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); |