Commit d48c0319 authored by Lukas Wunner's avatar Lukas Wunner Committed by Greg Kroah-Hartman
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sysfs: Add sysfs_bin_attr_simple_read() helper 



When drivers expose a bin_attribute in sysfs which is backed by a buffer
in memory, a common pattern is to set the @private and @size members in
struct bin_attribute to the buffer's location and size.

The ->read() callback then merely consists of a single memcpy() call.
It's not even necessary to perform bounds checks as these are already
handled by sysfs_kf_bin_read().

However each driver is so far providing its own ->read() implementation.
The pattern is sufficiently frequent to merit a public helper, so add
sysfs_bin_attr_simple_read() as well as BIN_ATTR_SIMPLE_RO() and
BIN_ATTR_SIMPLE_ADMIN_RO() macros to ease declaration of such
bin_attributes and reduce LoC and .text section size.

Signed-off-by: default avatarLukas Wunner <lukas@wunner.de>
Reviewed-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: default avatarArd Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/5ed62b197a442ec6db53d8746d9d806dd0576e2d.1712410202.git.lukas@wunner.de


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 85d2b0aa

fs/sysfs/file.c

+27 −0
Original line number Diff line number Diff line
@@ -783,3 +783,30 @@ int sysfs_emit_at(char *buf, int at, const char *fmt, ...) 
	return len;

}

EXPORT_SYMBOL_GPL(sysfs_emit_at);



/**

 *	sysfs_bin_attr_simple_read - read callback to simply copy from memory.

 *	@file:	attribute file which is being read.

 *	@kobj:	object to which the attribute belongs.

 *	@attr:	attribute descriptor.

 *	@buf:	destination buffer.

 *	@off:	offset in bytes from which to read.

 *	@count:	maximum number of bytes to read.

 *

 * Simple ->read() callback for bin_attributes backed by a buffer in memory.

 * The @private and @size members in struct bin_attribute must be set to the

 * buffer's location and size before the bin_attribute is created in sysfs.

 *

 * Bounds check for @off and @count is done in sysfs_kf_bin_read().

 * Negative value check for @off is done in vfs_setpos() and default_llseek().

 *

 * Returns number of bytes written to @buf.

 */

ssize_t sysfs_bin_attr_simple_read(struct file *file, struct kobject *kobj,

				   struct bin_attribute *attr, char *buf,

				   loff_t off, size_t count)

{

	memcpy(buf, attr->private + off, count);

	return count;

}

EXPORT_SYMBOL_GPL(sysfs_bin_attr_simple_read);

include/linux/sysfs.h

+15 −0
Original line number Diff line number Diff line
@@ -371,6 +371,17 @@ struct bin_attribute bin_attr_##_name = __BIN_ATTR_ADMIN_RO(_name, _size) 
#define BIN_ATTR_ADMIN_RW(_name, _size)					\

struct bin_attribute bin_attr_##_name = __BIN_ATTR_ADMIN_RW(_name, _size)



#define __BIN_ATTR_SIMPLE_RO(_name, _mode) {				\

	.attr	= { .name = __stringify(_name), .mode = _mode },	\

	.read	= sysfs_bin_attr_simple_read,				\

}



#define BIN_ATTR_SIMPLE_RO(_name)					\

struct bin_attribute bin_attr_##_name = __BIN_ATTR_SIMPLE_RO(_name, 0444)



#define BIN_ATTR_SIMPLE_ADMIN_RO(_name)					\

struct bin_attribute bin_attr_##_name = __BIN_ATTR_SIMPLE_RO(_name, 0400)



struct sysfs_ops {

	ssize_t	(*show)(struct kobject *, struct attribute *, char *);

	ssize_t	(*store)(struct kobject *, struct attribute *, const char *, size_t);
@@ -478,6 +489,10 @@ int sysfs_emit(char *buf, const char *fmt, ...); 
__printf(3, 4)

int sysfs_emit_at(char *buf, int at, const char *fmt, ...);



ssize_t sysfs_bin_attr_simple_read(struct file *file, struct kobject *kobj,

				   struct bin_attribute *attr, char *buf,

				   loff_t off, size_t count);



#else /* CONFIG_SYSFS */



static inline int sysfs_create_dir_ns(struct kobject *kobj, const void *ns)