[PATCH] libfs: add simple attribute files

Based on the discussion about spufs attributes, this is my suggestion
for a more generic attribute file support that can be used by both
debugfs and spufs.

Simple attribute files behave similarly to sequential files from
a kernel programmers perspective in that a standard set of file
operations is provided and only an open operation needs to
be written that registers file specific get() and set() functions.

These operations are defined as

void foo_set(void *data, u64 val); and
u64 foo_get(void *data);

where data is the inode->u.generic_ip pointer of the file and the
operations just need to make send of that pointer. The infrastructure
makes sure this works correctly with concurrent access and partial
read calls.

A macro named DEFINE_SIMPLE_ATTRIBUTE is provided to further simplify
using the attributes.

This patch already contains the changes for debugfs to use attributes
for its internal file operations.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 29 insertions, 38 deletions

diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index 548556ff250..efc97d9b786 100644
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -45,44 +45,15 @@ struct file_operations debugfs_file_operations = {
 	.open =		default_open,
 };
 
-#define simple_type(type, format, temptype, strtolfn)				\
-static ssize_t read_file_##type(struct file *file, char __user *user_buf,	\
-				size_t count, loff_t *ppos)			\
-{										\
-	char buf[32];								\
-	type *val = file->private_data;						\
-										\
-	snprintf(buf, sizeof(buf), format "\n", *val);				\
-	return simple_read_from_buffer(user_buf, count, ppos, buf, strlen(buf));\
-}										\
-static ssize_t write_file_##type(struct file *file, const char __user *user_buf,\
-				 size_t count, loff_t *ppos)			\
-{										\
-	char *endp;								\
-	char buf[32];								\
-	int buf_size;								\
-	type *val = file->private_data;						\
-	temptype tmp;								\
-										\
-	memset(buf, 0x00, sizeof(buf));						\
-	buf_size = min(count, (sizeof(buf)-1));					\
-	if (copy_from_user(buf, user_buf, buf_size))				\
-		return -EFAULT;							\
-										\
-	tmp = strtolfn(buf, &endp, 0);						\
-	if ((endp == buf) || ((type)tmp != tmp))				\
-		return -EINVAL;							\
-	*val = tmp;								\
-	return count;								\
-}										\
-static struct file_operations fops_##type = {					\
-	.read =		read_file_##type,					\
-	.write =	write_file_##type,					\
-	.open =		default_open,						\
-};
-simple_type(u8, "%c", unsigned long, simple_strtoul);
-simple_type(u16, "%hi", unsigned long, simple_strtoul);
-simple_type(u32, "%i", unsigned long, simple_strtoul);
+static void debugfs_u8_set(void *data, u64 val)
+{
+	*(u8 *)data = val;
+}
+static u64 debugfs_u8_get(void *data)
+{
+	return *(u8 *)data;
+}
+DEFINE_SIMPLE_ATTRIBUTE(fops_u8, debugfs_u8_get, debugfs_u8_set, "%llu\n");
 
 /**
  * debugfs_create_u8 - create a file in the debugfs filesystem that is used to read and write a unsigned 8 bit value.
@@ -116,6 +87,16 @@ struct dentry *debugfs_create_u8(const char *name, mode_t mode,
 }
 EXPORT_SYMBOL_GPL(debugfs_create_u8);
 
+static void debugfs_u16_set(void *data, u64 val)
+{
+	*(u16 *)data = val;
+}
+static u64 debugfs_u16_get(void *data)
+{
+	return *(u16 *)data;
+}
+DEFINE_SIMPLE_ATTRIBUTE(fops_u16, debugfs_u16_get, debugfs_u16_set, "%llu\n");
+
 /**
  * debugfs_create_u16 - create a file in the debugfs filesystem that is used to read and write a unsigned 8 bit value.
  *
@@ -148,6 +129,16 @@ struct dentry *debugfs_create_u16(const char *name, mode_t mode,
 }
 EXPORT_SYMBOL_GPL(debugfs_create_u16);
 
+static void debugfs_u32_set(void *data, u64 val)
+{
+	*(u32 *)data = val;
+}
+static u64 debugfs_u32_get(void *data)
+{
+	return *(u32 *)data;
+}
+DEFINE_SIMPLE_ATTRIBUTE(fops_u32, debugfs_u32_get, debugfs_u32_set, "%llu\n");
+
 /**
  * debugfs_create_u32 - create a file in the debugfs filesystem that is used to read and write a unsigned 8 bit value.
  *