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Subject[patch 1/3] vfs: introduce perform_write in a_ops
From: Nick Piggin <npiggin@suse.de>

Introduce a new perform_write() address space operation.

This is a single-call, bulk version of write_begin/write_end
operations. It is only used in the buffered write path (write_begin
must still be implemented), and not for in-kernel writes to pagecache.

For some filesystems, using this can provide significant speedups.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---
Index: linux/include/linux/fs.h
===================================================================
--- linux.orig/include/linux/fs.h 2008-02-04 15:24:03.000000000 +0100
+++ linux/include/linux/fs.h 2008-02-04 16:24:19.000000000 +0100
@@ -469,6 +469,9 @@ struct address_space_operations {
loff_t pos, unsigned len, unsigned copied,
struct page *page, void *fsdata);

+ ssize_t (*perform_write)(struct file *, struct address_space *mapping,
+ struct iov_iter *i, loff_t pos);
+
/* Unfortunately this kludge is needed for FIBMAP. Don't use it */
sector_t (*bmap)(struct address_space *, sector_t);
void (*invalidatepage) (struct page *, unsigned long);
Index: linux/mm/filemap.c
===================================================================
--- linux.orig/mm/filemap.c 2008-02-04 15:24:03.000000000 +0100
+++ linux/mm/filemap.c 2008-02-04 16:22:55.000000000 +0100
@@ -2312,7 +2312,9 @@ generic_file_buffered_write(struct kiocb
struct iov_iter i;

iov_iter_init(&i, iov, nr_segs, count, written);
- if (a_ops->write_begin)
+ if (a_ops->perform_write)
+ status = a_ops->perform_write(file, mapping, &i, pos);
+ else if (a_ops->write_begin)
status = generic_perform_write(file, &i, pos);
else
status = generic_perform_write_2copy(file, &i, pos);
Index: linux/Documentation/filesystems/vfs.txt
===================================================================
--- linux.orig/Documentation/filesystems/vfs.txt 2008-02-04 12:28:50.000000000 +0100
+++ linux/Documentation/filesystems/vfs.txt 2008-02-04 16:23:44.000000000 +0100
@@ -533,6 +533,9 @@ struct address_space_operations {
int (*write_end)(struct file *, struct address_space *mapping,
loff_t pos, unsigned len, unsigned copied,
struct page *page, void *fsdata);
+ ssize_t (*perform_write)(struct file *, struct address_space *mapping,
+ struct iov_iter *i, loff_t pos);
+
sector_t (*bmap)(struct address_space *, sector_t);
int (*invalidatepage) (struct page *, unsigned long);
int (*releasepage) (struct page *, int);
@@ -664,6 +667,17 @@ struct address_space_operations {
Returns < 0 on failure, otherwise the number of bytes (<= 'copied')
that were able to be copied into pagecache.

+ perform_write: This is a single-call, bulk version of write_begin/write_end
+ operations. It is only used in the buffered write path (write_begin
+ must still be implemented), and not for in-kernel writes to pagecache.
+ It takes an iov_iter structure, which provides a descriptor for the
+ source data (and has associated iov_iter_xxx helpers to operate on
+ that data). There are also file, mapping, and pos arguments, which
+ specify the destination of the data.
+
+ Returns < 0 on failure if nothing was written out, otherwise returns
+ the number of bytes copied into pagecache.
+
bmap: called by the VFS to map a logical block offset within object to
physical block number. This method is used by the FIBMAP
ioctl and for working with swap-files. To be able to swap to
--


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