[PATCH 2/3] overlayfs: Implement f_op->syncfs() call

[Vivek Goyal <vgoyal@redhat.com>]

Provide an implementation for ->syncfs(). Now if there is an error
returned by sync_filesystem(upper_sb), it will be visible to user
space. Currently in ovl_sync_fs() path, this error is ignored by VFS.

A later patch also adds logic to detect writeback error.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
---
 fs/overlayfs/file.c      |  1 +
 fs/overlayfs/overlayfs.h |  3 +++
 fs/overlayfs/readdir.c   |  1 +
 fs/overlayfs/super.c     | 30 ++++++++++++++++++++++++++++++
 4 files changed, 35 insertions(+)

diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
index efccb7c1f9bc..affc1ba63202 100644
--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -806,6 +806,7 @@ const struct file_operations ovl_file_operations = {
 
 	.copy_file_range	= ovl_copy_file_range,
 	.remap_file_range	= ovl_remap_file_range,
+	.syncfs			= ovl_syncfs,
 };
 
 int __init ovl_aio_request_cache_init(void)
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index f8880aa2ba0e..1efb13800755 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -520,3 +520,6 @@ int ovl_set_origin(struct dentry *dentry, struct dentry *lower,
 
 /* export.c */
 extern const struct export_operations ovl_export_operations;
+
+/* super.c */
+int ovl_syncfs(struct file *file);
diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
index 01620ebae1bd..e89b450c8f8f 100644
--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -975,6 +975,7 @@ const struct file_operations ovl_dir_operations = {
 #ifdef CONFIG_COMPAT
 	.compat_ioctl	= ovl_compat_ioctl,
 #endif
+	.syncfs		= ovl_syncfs,
 };
 
 int ovl_check_empty_dir(struct dentry *dentry, struct list_head *list)
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 290983bcfbb3..b4d92e6fa5ce 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -286,6 +286,36 @@ static int ovl_sync_fs(struct super_block *sb, int wait)
 	return ret;
 }
 
+int ovl_syncfs(struct file *file)
+{
+	struct super_block *sb = file->f_path.dentry->d_sb;
+	struct ovl_fs *ofs = sb->s_fs_info;
+	struct super_block *upper_sb;
+	int ret;
+
+	ret = 0;
+	down_read(&sb->s_umount);
+	if (sb_rdonly(sb))
+		goto out;
+
+	if (!ovl_upper_mnt(ofs))
+		goto out;
+
+	if (!ovl_should_sync(ofs))
+		goto out;
+
+	upper_sb = ovl_upper_mnt(ofs)->mnt_sb;
+
+	down_read(&upper_sb->s_umount);
+	ret = sync_filesystem(upper_sb);
+	up_read(&upper_sb->s_umount);
+
+
+out:
+	up_read(&sb->s_umount);
+	return ret;
+}
+
 /**
  * ovl_statfs
  * @sb: The overlayfs super block
-- 
2.25.4