introduce __block_write_begin

Split up the block_write_begin implementation - __block_write_begin is a new
trivial wrapper for block_prepare_write that always takes an already
allocated page and can be either called from block_write_begin or filesystem
code that already has a page allocated.  Remove the handling of already
allocated pages from block_write_begin after switching all callers that
do it to __block_write_begin.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

fs/buffer.c

@@ -1833,9 +1833,10 @@ void page_zero_new_buffers(struct page *page, unsigned from, unsigned to)
 }
 EXPORT_SYMBOL(page_zero_new_buffers);
 
-static int __block_prepare_write(struct inode *inode, struct page *page,
-		unsigned from, unsigned to, get_block_t *get_block)
+int block_prepare_write(struct page *page, unsigned from, unsigned to,
+		get_block_t *get_block)
 {
+	struct inode *inode = page->mapping->host;
 	unsigned block_start, block_end;
 	sector_t block;
 	int err = 0;
@@ -1908,10 +1909,13 @@ static int __block_prepare_write(struct inode *inode, struct page *page,
 		if (!buffer_uptodate(*wait_bh))
 			err = -EIO;
 	}
-	if (unlikely(err))
+	if (unlikely(err)) {
 		page_zero_new_buffers(page, from, to);
+		ClearPageUptodate(page);
+	}
 	return err;
 }
+EXPORT_SYMBOL(block_prepare_write);
 
 static int __block_commit_write(struct inode *inode, struct page *page,
 		unsigned from, unsigned to)
@@ -1948,6 +1952,15 @@ static int __block_commit_write(struct inode *inode, struct page *page,
 	return 0;
 }
 
+int __block_write_begin(struct page *page, loff_t pos, unsigned len,
+		get_block_t *get_block)
+{
+	unsigned start = pos & (PAGE_CACHE_SIZE - 1);
+
+	return block_prepare_write(page, start, start + len, get_block);
+}
+EXPORT_SYMBOL(__block_write_begin);
+
 /*
  * Filesystems implementing the new truncate sequence should use the
  * _newtrunc postfix variant which won't incorrectly call vmtruncate.
@@ -1958,41 +1971,22 @@ int block_write_begin_newtrunc(struct file *file, struct address_space *mapping,
 			struct page **pagep, void **fsdata,
 			get_block_t *get_block)
 {
-	struct inode *inode = mapping->host;
-	int status = 0;
+	pgoff_t index = pos >> PAGE_CACHE_SHIFT;
 	struct page *page;
-	pgoff_t index;
-	unsigned start, end;
-	int ownpage = 0;
-
-	index = pos >> PAGE_CACHE_SHIFT;
-	start = pos & (PAGE_CACHE_SIZE - 1);
-	end = start + len;
+	int status;
 
-	page = *pagep;
-	if (page == NULL) {
-		ownpage = 1;
 	page = grab_cache_page_write_begin(mapping, index, flags);
-		if (!page) {
-			status = -ENOMEM;
-			goto out;
-		}
-		*pagep = page;
-	} else
-		BUG_ON(!PageLocked(page));
+	if (!page)
+		return -ENOMEM;
 
-	status = __block_prepare_write(inode, page, start, end, get_block);
+	status = __block_write_begin(page, pos, len, get_block);
 	if (unlikely(status)) {
-		ClearPageUptodate(page);
-
-		if (ownpage) {
 		unlock_page(page);
 		page_cache_release(page);
-			*pagep = NULL;
-		}
+		page = NULL;
 	}
 
-out:
+	*pagep = page;
 	return status;
 }
 EXPORT_SYMBOL(block_write_begin_newtrunc);
@@ -2379,17 +2373,6 @@ int cont_write_begin(struct file *file, struct address_space *mapping,
 }
 EXPORT_SYMBOL(cont_write_begin);
 
-int block_prepare_write(struct page *page, unsigned from, unsigned to,
-			get_block_t *get_block)
-{
-	struct inode *inode = page->mapping->host;
-	int err = __block_prepare_write(inode, page, from, to, get_block);
-	if (err)
-		ClearPageUptodate(page);
-	return err;
-}
-EXPORT_SYMBOL(block_prepare_write);
-
 int block_commit_write(struct page *page, unsigned from, unsigned to)
 {
 	struct inode *inode = page->mapping->host;

fs/ext2/dir.c

@@ -450,8 +450,7 @@ ino_t ext2_inode_by_name(struct inode *dir, struct qstr *child)
 
 static int ext2_prepare_chunk(struct page *page, loff_t pos, unsigned len)
 {
-	return block_write_begin_newtrunc(NULL, page->mapping, pos, len, 0,
-					  &page, NULL, ext2_get_block);
+	return __block_write_begin(page, pos, len, ext2_get_block);
 }
 
 /* Releases the page */

fs/ext3/inode.c

@@ -1196,8 +1196,7 @@ static int ext3_write_begin(struct file *file, struct address_space *mapping,
 		ret = PTR_ERR(handle);
 		goto out;
 	}
-	ret = block_write_begin(file, mapping, pos, len, flags, pagep, fsdata,
-							ext3_get_block);
+	ret = __block_write_begin(page, pos, len, ext3_get_block);
 	if (ret)
 		goto write_begin_failed;
 

fs/ext4/inode.c

@@ -1578,11 +1578,9 @@ static int ext4_write_begin(struct file *file, struct address_space *mapping,
 	*pagep = page;
 
 	if (ext4_should_dioread_nolock(inode))
-		ret = block_write_begin(file, mapping, pos, len, flags, pagep,
-				fsdata, ext4_get_block_write);
+		ret = __block_write_begin(page, pos, len, ext4_get_block_write);
 	else
-		ret = block_write_begin(file, mapping, pos, len, flags, pagep,
-				fsdata, ext4_get_block);
+		ret = __block_write_begin(page, pos, len, ext4_get_block);
 
 	if (!ret && ext4_should_journal_data(inode)) {
 		ret = walk_page_buffers(handle, page_buffers(page),
@@ -1593,7 +1591,7 @@ static int ext4_write_begin(struct file *file, struct address_space *mapping,
 		unlock_page(page);
 		page_cache_release(page);
 		/*
-		 * block_write_begin may have instantiated a few blocks
+		 * __block_write_begin may have instantiated a few blocks
 		 * outside i_size.  Trim these off again. Don't need
 		 * i_size_read because we hold i_mutex.
 		 *
@@ -3185,8 +3183,7 @@ static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
 	}
 	*pagep = page;
 
-	ret = block_write_begin(file, mapping, pos, len, flags, pagep, fsdata,
-				ext4_da_get_block_prep);
+	ret = __block_write_begin(page, pos, len, ext4_da_get_block_prep);
 	if (ret < 0) {
 		unlock_page(page);
 		ext4_journal_stop(handle);

fs/minix/inode.c

@@ -359,8 +359,7 @@ static int minix_readpage(struct file *file, struct page *page)
 
 int minix_prepare_chunk(struct page *page, loff_t pos, unsigned len)
 {
-	return block_write_begin_newtrunc(NULL, page->mapping, pos, len, 0,
-					  &page, NULL, minix_get_block);
+	return __block_write_begin(page, pos, len, minix_get_block);
 }
 
 static int minix_write_begin(struct file *file, struct address_space *mapping,

fs/nilfs2/dir.c

@@ -83,8 +83,7 @@ static unsigned nilfs_last_byte(struct inode *inode, unsigned long page_nr)
 static int nilfs_prepare_chunk(struct page *page, unsigned from, unsigned to)
 {
 	loff_t pos = page_offset(page) + from;
-	return block_write_begin_newtrunc(NULL, page->mapping, pos, to - from,
-					  0, &page, NULL, nilfs_get_block);
+	return __block_write_begin(page, pos, to - from, nilfs_get_block);
 }
 
 static void nilfs_commit_chunk(struct page *page,

fs/reiserfs/inode.c

@@ -2585,8 +2585,7 @@ static int reiserfs_write_begin(struct file *file,
 		old_ref = th->t_refcount;
 		th->t_refcount++;
 	}
-	ret = block_write_begin(file, mapping, pos, len, flags, pagep, fsdata,
-				reiserfs_get_block);
+	ret = __block_write_begin(page, pos, len, reiserfs_get_block);
 	if (ret && reiserfs_transaction_running(inode->i_sb)) {
 		struct reiserfs_transaction_handle *th = current->journal_info;
 		/* this gets a little ugly.  If reiserfs_get_block returned an

fs/sysv/itree.c

@@ -461,8 +461,7 @@ static int sysv_readpage(struct file *file, struct page *page)
 
 int sysv_prepare_chunk(struct page *page, loff_t pos, unsigned len)
 {
-	return block_write_begin_newtrunc(NULL, page->mapping, pos, len, 0,
-					  &page, NULL, get_block);
+	return __block_write_begin(page, pos, len, get_block);
 }
 
 static int sysv_write_begin(struct file *file, struct address_space *mapping,

fs/ufs/inode.c

@@ -560,8 +560,7 @@ static int ufs_readpage(struct file *file, struct page *page)
 
 int ufs_prepare_chunk(struct page *page, loff_t pos, unsigned len)
 {
-	return block_write_begin_newtrunc(NULL, page->mapping, pos, len, 0,
-					  &page, NULL, ufs_getfrag_block);
+	return __block_write_begin(page, pos, len, ufs_getfrag_block);
 }
 
 static int ufs_write_begin(struct file *file, struct address_space *mapping,

include/linux/buffer_head.h

@@ -209,6 +209,8 @@ int block_write_begin_newtrunc(struct file *, struct address_space *,
 int block_write_begin(struct file *, struct address_space *,
 				loff_t, unsigned, unsigned,
 				struct page **, void **, get_block_t*);
+int __block_write_begin(struct page *page, loff_t pos, unsigned len,
+		get_block_t *get_block);
 int block_write_end(struct file *, struct address_space *,
 				loff_t, unsigned, unsigned,
 				struct page *, void *);