introduce memory_read_from_buffer()

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>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Doug Warzecha <Douglas_Warzecha@dell.com>
Cc: Zhang Rui <rui.zhang@intel.com>
Cc: Matt Domsch <Matt_Domsch@dell.com>
Cc: Abhay Salunke <Abhay_Salunke@dell.com>
Cc: Greg Kroah-Hartman <gregkh@suse.de>
Cc: Markus Rechberger <markus.rechberger@amd.com>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Cc: Bob Moore <robert.moore@intel.com>
Cc: Thomas Renninger <trenn@suse.de>
Cc: Len Brown <lenb@kernel.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Cc: Krzysztof Helt <krzysztof.h1@poczta.fm>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Peter Oberparleiter <peter.oberparleiter@de.ibm.com>
Cc: Michael Holzheu <holzheu@de.ibm.com>
Cc: Brian King <brking@us.ibm.com>
Cc: James E.J. Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Andrew Vasquez <linux-driver@qlogic.com>
Cc: Seokmann Ju <seokmann.ju@qlogic.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 22 insertions, 1 deletions

diff --git a/fs/libfs.c b/fs/libfs.c
index b004dfadd891..892d41cb3382 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -528,6 +528,23 @@ ssize_t simple_read_from_buffer(void __user *to, size_t count, loff_t *ppos,
         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);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index f413085f748e..d490779f18d9 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2000,7 +2000,10 @@ extern int simple_fill_super(struct super_block *, int, struct tree_descr *);
 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 *,