linux-kernel - [PATCH V6 1/2] FS: Add generic data flush to fsync

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Message-Id: <20140515203302.e6e712e73046a187887a186c@skynet.be>
Date:	Thu, 15 May 2014 20:33:02 +0200
From:	Fabian Frederick <fabf@...net.be>
To:	linux-kernel <linux-kernel@...r.kernel.org>
Cc:	jack <jack@...e.cz>, hch <hch@...radead.org>,
	Viro <viro@...iv.linux.org.uk>, akpm <akpm@...ux-foundation.org>,
	tytso <tytso@....edu>
Subject: [PATCH V6 1/2] FS: 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."

Suggested-by: Jan Kara <jack@...e.cz>
Suggested-by: Christoph Hellwig <hch@...radead.org>
Cc: Jan Kara <jack@...e.cz>
Cc: Christoph Hellwig <hch@...radead.org>
Cc: Alexander Viro <viro@...iv.linux.org.uk>
Cc: "Theodore Ts'o" <tytso@....edu>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Fabian Frederick <fabf@...net.be>
---
v6: 
   -Complete description (Jan Kara)
   -#ifdef CONFIG_BLOCK (Andrew Morton/Jan Kara)
v5: patch2/2 ext4 patch fix (Thanks to Ming Lei)
V4: update description
V3: __generic_file_fsync = no flush
V2: No additional flag
V1: First version with MS_BARRIER flag

 fs/libfs.c         | 39 ++++++++++++++++++++++++++++++++++++---
 include/linux/fs.h |  1 +
 2 files changed, 37 insertions(+), 3 deletions(-)

diff --git a/fs/libfs.c b/fs/libfs.c
index a184424..3a704e1 100644
--- a/fs/libfs.c
+++ b/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 +956,39 @@ 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;
+#ifdef CONFIG_BLOCK
+	return blkdev_issue_flush(inode->i_sb->s_bdev, GFP_KERNEL, NULL);
+#else
+	return err;
+#endif
+
+}
 EXPORT_SYMBOL(generic_file_fsync);
 
 /**
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 8780312..c3f46e4 100644
--- a/include/linux/fs.h
+++ b/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);
-- 
1.8.4.5

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