fs/libfs.c: add generic data flush to fsync

Description by Jan Kara:
 "A lot of older filesystems don't properly flush volatile disk caches
  on fsync(2) which can lead to loss of fsynced data after power failure.

This patch makes generic_file_fsync() issue proper cache flush to fix the
problem.  Sysadmin can use /sys/devices/.../cache_type to tell the system
it should not send the cache flush."

[akpm@linux-foundation.org: nuke ifdef]
[akpm@linux-foundation.org: fix warning]
Signed-off-by: NFabian Frederick <fabf@skynet.be>
Suggested-by: NJan Kara <jack@suse.cz>
Suggested-by: NChristoph Hellwig <hch@infradead.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

fs/libfs.c

@@ -3,6 +3,7 @@
  *	Library for filesystems writers.
  */
 
+#include <linux/blkdev.h>
 #include <linux/export.h>
 #include <linux/pagemap.h>
 #include <linux/slab.h>
@@ -923,16 +924,19 @@ struct dentry *generic_fh_to_parent(struct super_block *sb, struct fid *fid,
 EXPORT_SYMBOL_GPL(generic_fh_to_parent);
 
 /**
- * generic_file_fsync - generic fsync implementation for simple filesystems
+ * __generic_file_fsync - generic fsync implementation for simple filesystems
+ *
  * @file:	file to synchronize
+ * @start:	start offset in bytes
+ * @end:	end offset in bytes (inclusive)
  * @datasync:	only synchronize essential metadata if true
  *
  * This is a generic implementation of the fsync method for simple
  * filesystems which track all non-inode metadata in the buffers list
  * hanging off the address_space structure.
  */
-int generic_file_fsync(struct file *file, loff_t start, loff_t end,
-		       int datasync)
+int __generic_file_fsync(struct file *file, loff_t start, loff_t end,
+				 int datasync)
 {
 	struct inode *inode = file->f_mapping->host;
 	int err;
@@ -952,10 +956,34 @@ int generic_file_fsync(struct file *file, loff_t start, loff_t end,
 	err = sync_inode_metadata(inode, 1);
 	if (ret == 0)
 		ret = err;
+
 out:
 	mutex_unlock(&inode->i_mutex);
 	return ret;
 }
+EXPORT_SYMBOL(__generic_file_fsync);
+
+/**
+ * generic_file_fsync - generic fsync implementation for simple filesystems
+ *			with flush
+ * @file:	file to synchronize
+ * @start:	start offset in bytes
+ * @end:	end offset in bytes (inclusive)
+ * @datasync:	only synchronize essential metadata if true
+ *
+ */
+
+int generic_file_fsync(struct file *file, loff_t start, loff_t end,
+		       int datasync)
+{
+	struct inode *inode = file->f_mapping->host;
+	int err;
+
+	err = __generic_file_fsync(file, start, end, datasync);
+	if (err)
+		return err;
+	return blkdev_issue_flush(inode->i_sb->s_bdev, GFP_KERNEL, NULL);
+}
 EXPORT_SYMBOL(generic_file_fsync);
 
 /**

include/linux/blkdev.h

@@ -1607,6 +1607,9 @@ struct block_device_operations {
 extern int __blkdev_driver_ioctl(struct block_device *, fmode_t, unsigned int,
 				 unsigned long);
 #else /* CONFIG_BLOCK */
+
+struct block_device;
+
 /*
  * stubs for when the block layer is configured out
  */
@@ -1642,6 +1645,12 @@ static inline bool blk_needs_flush_plug(struct task_struct *tsk)
 	return false;
 }
 
+static inline int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
+				     sector_t *error_sector)
+{
+	return 0;
+}
+
 #endif /* CONFIG_BLOCK */
 
 #endif

include/linux/fs.h

@@ -2590,6 +2590,7 @@ extern ssize_t simple_read_from_buffer(void __user *to, size_t count,
 extern ssize_t simple_write_to_buffer(void *to, size_t available, loff_t *ppos,
 		const void __user *from, size_t count);
 
+extern int __generic_file_fsync(struct file *, loff_t, loff_t, int);
 extern int generic_file_fsync(struct file *, loff_t, loff_t, int);
 
 extern int generic_check_addressable(unsigned, u64);