fs: push i_mutex and filemap_write_and_wait down into ->fsync() handlers

Btrfs needs to be able to control how filemap_write_and_wait_range() is called
in fsync to make it less of a painful operation, so push down taking i_mutex and
the calling of filemap_write_and_wait() down into the ->fsync() handlers.  Some
file systems can drop taking the i_mutex altogether it seems, like ext3 and
ocfs2.  For correctness sake I just pushed everything down in all cases to make
sure that we keep the current behavior the same for everybody, and then each
individual fs maintainer can make up their mind about what to do from there.
Thanks,

Acked-by: Jan Kara <jack@suse.cz>
Signed-off-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Conflicts:
	Documentation/filesystems/porting

Change-Id: I7697244cce355e6d443a39c5133a5c94f02e199b

2 files changed, 15 insertions, 5 deletions

diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index 1f3624d..64311e0 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -750,7 +750,7 @@ extern void afs_pages_written_back(struct afs_vnode *, struct afs_call *);
 extern ssize_t afs_file_write(struct kiocb *, const struct iovec *,
 			      unsigned long, loff_t);
 extern int afs_writeback_all(struct afs_vnode *);
-extern int afs_fsync(struct file *, int);
+extern int afs_fsync(struct file *, loff_t, loff_t, int);
 
 
 /*****************************************************************************/
diff --git a/fs/afs/write.c b/fs/afs/write.c
index b806285..9aa52d9 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -681,9 +681,10 @@ int afs_writeback_all(struct afs_vnode *vnode)
  * - the return status from this call provides a reliable indication of
  *   whether any write errors occurred for this process.
  */
-int afs_fsync(struct file *file, int datasync)
+int afs_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 {
 	struct dentry *dentry = file->f_path.dentry;
+	struct inode *inode = file->f_mapping->host;
 	struct afs_writeback *wb, *xwb;
 	struct afs_vnode *vnode = AFS_FS_I(dentry->d_inode);
 	int ret;
@@ -692,12 +693,19 @@ int afs_fsync(struct file *file, int datasync)
 	       vnode->fid.vid, vnode->fid.vnode, dentry->d_name.name,
 	       datasync);
 
+	ret = filemap_write_and_wait_range(inode->i_mapping, start, end);
+	if (ret)
+		return ret;
+	mutex_lock(&inode->i_mutex);
+
 	/* use a writeback record as a marker in the queue - when this reaches
 	 * the front of the queue, all the outstanding writes are either
 	 * completed or rejected */
 	wb = kzalloc(sizeof(*wb), GFP_KERNEL);
-	if (!wb)
-		return -ENOMEM;
+	if (!wb) {
+		ret = -ENOMEM;
+		goto out;
+	}
 	wb->vnode = vnode;
 	wb->first = 0;
 	wb->last = -1;
@@ -720,7 +728,7 @@ int afs_fsync(struct file *file, int datasync)
 	if (ret < 0) {
 		afs_put_writeback(wb);
 		_leave(" = %d [wb]", ret);
-		return ret;
+		goto out;
 	}
 
 	/* wait for the preceding writes to actually complete */
@@ -729,6 +737,8 @@ int afs_fsync(struct file *file, int datasync)
 				       vnode->writebacks.next == &wb->link);
 	afs_put_writeback(wb);
 	_leave(" = %d", ret);
+out:
+	mutex_unlock(&inode->i_mutex);
 	return ret;
 }