[PATCH 2/2] fs: use simple_prepare_write to zero page data

[Nate Diller <nate.diller@gmail.com>]

It's common for file systems to need to zero data on either side of a write,
if a page is not Uptodate during prepare_write.  It just so happens that
simple_prepare_write() in libfs.c does exactly that, so we can avoid
duplication and just call that function to zero page data.

Compile tested on x86_64.

signed-off-by: Nate Diller <nate.diller@gmail.com>

---

 cifs/file.c                           |    9 +--------
 ext4/writeback.c                      |   17 +----------------
 reiser4/plugin/item/extent_file_ops.c |   13 +++----------
 3 files changed, 5 insertions(+), 34 deletions(-)

---

diff -urpN -X dontdiff linux-2.6.21-rc6-mm1/fs/cifs/file.c linux-2.6.21-rc6-mm1-test/fs/cifs/file.c
--- linux-2.6.21-rc6-mm1/fs/cifs/file.c	2007-04-09 18:25:37.000000000 -0700
+++ linux-2.6.21-rc6-mm1-test/fs/cifs/file.c	2007-04-09 18:23:16.000000000 -0700
@@ -1955,14 +1955,7 @@ static int cifs_prepare_write(struct fil
 		 * We don't need to read data beyond the end of the file.
 		 * zero it, and set the page uptodate
 		 */
-		void *kaddr = kmap_atomic(page, KM_USER0);
-
-		if (from)
-			memset(kaddr, 0, from);
-		if (to < PAGE_CACHE_SIZE)
-			memset(kaddr + to, 0, PAGE_CACHE_SIZE - to);
-		flush_dcache_page(page);
-		kunmap_atomic(kaddr, KM_USER0);
+		simple_prepare_write(file, page, from, to);
 		SetPageUptodate(page);
 	} else if ((file->f_flags & O_ACCMODE) != O_WRONLY) {
 		/* might as well read a page, it is fast enough */
diff -urpN -X dontdiff linux-2.6.21-rc6-mm1/fs/ext4/writeback.c linux-2.6.21-rc6-mm1-test/fs/ext4/writeback.c
--- linux-2.6.21-rc6-mm1/fs/ext4/writeback.c	2007-04-09 18:32:52.000000000 -0700
+++ linux-2.6.21-rc6-mm1-test/fs/ext4/writeback.c	2007-04-09 18:23:16.000000000 -0700
@@ -819,21 +819,6 @@ int ext4_wb_writepages(struct address_sp
 	return 0;
 }
 
-static void ext4_wb_clear_page(struct page *page, int from, int to)
-{
-	void *kaddr;
-
-	if (to < PAGE_CACHE_SIZE || from > 0) {
-		kaddr = kmap_atomic(page, KM_USER0);
-		if (PAGE_CACHE_SIZE > to)
-			memset(kaddr + to, 0, PAGE_CACHE_SIZE - to);
-		if (0 < from)
-			memset(kaddr, 0, from);
-		flush_dcache_page(page);
-		kunmap_atomic(kaddr, KM_USER0);
-	}
-}
-
 int ext4_wb_prepare_write(struct file *file, struct page *page,
 			      unsigned from, unsigned to)
 {
@@ -863,7 +848,7 @@ int ext4_wb_prepare_write(struct file *f
 			/* this block isn't allocated yet, reserve space */
 			wb_debug("reserve space for new block\n");
 			page->private = 1;
-			ext4_wb_clear_page(page, from, to);
+			simple_prepare_write(file, page, from, to);
 			ClearPageMappedToDisk(page);
 		} else { 
 			/* block is already mapped, so no need to reserve */
diff -urpN -X dontdiff linux-2.6.21-rc6-mm1/fs/reiser4/plugin/item/extent_file_ops.c linux-2.6.21-rc6-mm1-test/fs/reiser4/plugin/item/extent_file_ops.c
--- linux-2.6.21-rc6-mm1/fs/reiser4/plugin/item/extent_file_ops.c	2007-04-09 18:32:52.000000000 -0700
+++ linux-2.6.21-rc6-mm1-test/fs/reiser4/plugin/item/extent_file_ops.c	2007-04-09 18:31:34.000000000 -0700
@@ -1040,16 +1040,9 @@ ssize_t reiser4_write_extent(struct file
 		BUG_ON(get_current_context()->trans->atom != NULL);
 
 		lock_page(page);
-		if (!PageUptodate(page) && to_page != PAGE_CACHE_SIZE) {
-			void *kaddr;
-
-			kaddr = kmap_atomic(page, KM_USER0);
-			memset(kaddr, 0, page_off);
-			memset(kaddr + page_off + to_page, 0,
-			       PAGE_CACHE_SIZE - (page_off + to_page));
-			flush_dcache_page(page);
-			kunmap_atomic(kaddr, KM_USER0);
-		}
+		if (!PageUptodate(page) && to_page != PAGE_CACHE_SIZE)
+			simple_prepare_write(file, page, page_off,
+					     page_off + to_page);
 
 		written = filemap_copy_from_user(page, page_off, buf, to_page);
 		flush_dcache_page(page);