block: Add block_flush_device()

[Fernando Luis Vázquez Cao]

This patch adds a helper function that should be used by filesystems that need
to flush the underlying block device on fsync()/fdatasync().

Signed-off-by: Fernando Luis Vazquez Cao <fernando@xxxxxxxxxxxxx>
---

diff -urNp linux-2.6.29-rc3-orig/fs/buffer.c linux-2.6.29-rc3/fs/buffer.c
--- linux-2.6.29-rc3-orig/fs/buffer.c	2009-01-29 09:47:51.000000000 +0900
+++ linux-2.6.29-rc3/fs/buffer.c	2009-01-29 20:11:29.000000000 +0900
@@ -165,6 +165,24 @@ void end_buffer_write_sync(struct buffer
 	put_bh(bh);
 }
 
+/* Issue flush of write caches on the block device */
+int block_flush_device(struct super_block *sb)
+{
+	int ret = 0;
+
+	if (!(sb->s_flags & MS_FLUSHONFSYNC))
+		return ret;
+
+	ret = blkdev_issue_flush(sb->s_bdev, NULL);
+
+	if (ret == -EOPNOTSUPP)
+		return 0;
+
+	return ret;
+}
+EXPORT_SYMBOL(block_flush_device);
+
+
 /*
  * Write out and wait upon all the dirty data associated with a block
  * device via its mapping.  Does not take the superblock lock.
diff -urNp linux-2.6.29-rc3-orig/include/linux/buffer_head.h linux-2.6.29-rc3/include/linux/buffer_head.h
--- linux-2.6.29-rc3-orig/include/linux/buffer_head.h	2009-01-29 09:47:51.000000000 +0900
+++ linux-2.6.29-rc3/include/linux/buffer_head.h	2009-01-29 19:26:33.000000000 +0900
@@ -238,6 +238,7 @@ int nobh_write_end(struct file *, struct
 int nobh_truncate_page(struct address_space *, loff_t, get_block_t *);
 int nobh_writepage(struct page *page, get_block_t *get_block,
                         struct writeback_control *wbc);
+int block_flush_device(struct super_block *sb);
 
 void buffer_init(void);
 


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