udf: Add readpages support for udf.

Use mpage_readpages() instead of multiple calls to udf_readpage() to reduce the
CPU utilization and make performance higher.

Signed-off-by: Namjae Jeon <[e-mail]>
Signed-off-by: Jan Kara <[e-mail]>

fs/udf/inode.c

···
 #include <linux/writeback.h>
 #include <linux/slab.h>
 #include <linux/crc-itu-t.h>
+#include <linux/mpage.h>
 
 #include "udf_i.h"
 #include "udf_sb.h"
···
 
 static int udf_readpage(struct file *file, struct page *page)
 {
-	return block_read_full_page(page, udf_get_block);
+	return mpage_readpage(page, udf_get_block);
+}
+
+static int udf_readpages(struct file *file, struct address_space *mapping,
+			struct list_head *pages, unsigned nr_pages)
+{
+	return mpage_readpages(mapping, pages, nr_pages, udf_get_block);
 }
 
 static int udf_write_begin(struct file *file, struct address_space *mapping,
···
 
 const struct address_space_operations udf_aops = {
 	.readpage	= udf_readpage,
+	.readpages	= udf_readpages,
 	.writepage	= udf_writepage,
 	.write_begin		= udf_write_begin,
 	.write_end		= generic_write_end,