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@xxxxxxxxx>
---
fs/sysfs/file.c | 27 +++++++++++++++++++++++++++
include/linux/sysfs.h | 15 +++++++++++++++
2 files changed, 42 insertions(+)
diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index 6b7652f..289b57d 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -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);
diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
index 326341c..a7d725f 100644
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -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_group_change_owner(struct kobject *kobj,
__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)
--
2.43.0
