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

From: Fabian Frederick
Date: Thu May 15 2014 - 14:33:13 EST


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@xxxxxxx>
Suggested-by: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: "Theodore Ts'o" <tytso@xxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Fabian Frederick <fabf@xxxxxxxxx>
---
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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