[patch -v3 12/22] introduce memory_read_from_buffer

[Akinobu Mita <akinobu.mita@gmail.com>]

[-- Attachment #1: memory-read-from-buffer.patch --]
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This patch introduces memory_read_from_buffer.

The only difference between memory_read_from_buffer and simple_read_from_buffer
is which address space the function copies to.

simple_read_from_buffer copies to user space memory.
memory_read_from_buffer copies to normal memory.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
---
 fs/libfs.c         |   18 ++++++++++++++++++
 include/linux/fs.h |    5 ++++-
 2 files changed, 22 insertions(+), 1 deletion(-)

Index: 2.6-git/fs/libfs.c
===================================================================
--- 2.6-git.orig/fs/libfs.c
+++ 2.6-git/fs/libfs.c
@@ -528,6 +528,23 @@ ssize_t simple_read_from_buffer(void __u
 	return count;
 }
 
+ssize_t memory_read_from_buffer(void *to, size_t count, loff_t *ppos,
+				const void *from, size_t available)
+{
+	loff_t pos = *ppos;
+
+	if (pos < 0)
+		return -EINVAL;
+	if (pos >= available)
+		return 0;
+	if (count > available - pos)
+		count = available - pos;
+	memcpy(to, from + pos, count);
+	*ppos = pos + count;
+
+	return count;
+}
+
 /*
  * Transaction based IO.
  * The file expects a single write which triggers the transaction, and then
@@ -800,6 +817,7 @@ EXPORT_SYMBOL(simple_statfs);
 EXPORT_SYMBOL(simple_sync_file);
 EXPORT_SYMBOL(simple_unlink);
 EXPORT_SYMBOL(simple_read_from_buffer);
+EXPORT_SYMBOL(memory_read_from_buffer);
 EXPORT_SYMBOL(simple_transaction_get);
 EXPORT_SYMBOL(simple_transaction_read);
 EXPORT_SYMBOL(simple_transaction_release);
Index: 2.6-git/include/linux/fs.h
===================================================================
--- 2.6-git.orig/include/linux/fs.h
+++ 2.6-git/include/linux/fs.h
@@ -2000,7 +2000,10 @@ extern int simple_fill_super(struct supe
 extern int simple_pin_fs(struct file_system_type *, struct vfsmount **mount, int *count);
 extern void simple_release_fs(struct vfsmount **mount, int *count);
 
-extern ssize_t simple_read_from_buffer(void __user *, size_t, loff_t *, const void *, size_t);
+extern ssize_t simple_read_from_buffer(void __user *to, size_t count,
+			loff_t *ppos, const void *from, size_t available);
+extern ssize_t memory_read_from_buffer(void *to, size_t count, loff_t *ppos,
+			const void *from, size_t available);
 
 #ifdef CONFIG_MIGRATION
 extern int buffer_migrate_page(struct address_space *,

--