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sysfs: Add sysfs_bin_attr_simple_read() helper

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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: Lukas Wunner <lukas@wunner.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/5ed62b197a442ec6db53d8746d9d806dd0576e2d.1712410202.git.lukas@wunner.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Lukas Wunner 2024-04-06 15:52:01 +02:00 committed by Greg Kroah-Hartman
parent 85d2b0aa17
commit d48c03198a
2 changed files with 42 additions and 0 deletions
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27
fs/sysfs/file.c
View File

@ -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);

15
include/linux/sysfs.h
View File

@ -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)