[RFC PATCH 5/5] ovl: impement containerized syncfs for overlayfs

[Chengguang Xu <cgxu519@mykernel.net>]

Mark overlayfs' inode dirty when underlying upper inode becomes dirty,
then only sync overlayfs' dirty inodes while syncfs.

Signed-off-by: Chengguang Xu <cgxu519@mykernel.net>
---
 fs/overlayfs/inode.c | 24 ++++++++++++++++++++++++
 fs/overlayfs/super.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++----
 fs/overlayfs/util.c  |  3 +--
 3 files changed, 72 insertions(+), 6 deletions(-)

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index e75c7ec..c709aed 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -11,6 +11,7 @@
 #include <linux/posix_acl.h>
 #include <linux/ratelimit.h>
 #include <linux/fiemap.h>
+#include <linux/writeback.h>
 #include "overlayfs.h"
 
 
@@ -516,7 +517,30 @@ static int ovl_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 	.update_time	= ovl_update_time,
 };
 
+static int ovl_writepages(struct address_space *mapping, struct writeback_control *wbc)
+{
+	struct inode *inode = mapping->host;
+	struct inode *upper_inode = ovl_inode_upper(inode);
+	struct ovl_fs *ofs = inode->i_sb->s_fs_info;
+	struct writeback_control upper_wbc = {
+		.nr_to_write		= LONG_MAX,
+		.sync_mode		= WB_SYNC_ALL,
+		.for_kupdate		= wbc->for_kupdate,
+		.for_background		= wbc->for_background,
+		.for_sync		= 0,
+		.range_cyclic		= wbc->range_cyclic,
+		.range_start		= 0,
+		.range_end		= LLONG_MAX,
+	};
+
+	if (!ovl_should_sync(ofs))
+		return 0;
+
+	return writeback_single_inode(upper_inode, &upper_wbc);
+}
+
 static const struct address_space_operations ovl_aops = {
+	.writepages             = ovl_writepages,
 	/* For O_DIRECT dentry_open() checks f_mapping->a_ops->direct_IO */
 	.direct_IO		= noop_direct_IO,
 };
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 6d8f9da..da1b65a 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -15,6 +15,9 @@
 #include <linux/seq_file.h>
 #include <linux/posix_acl_xattr.h>
 #include <linux/exportfs.h>
+#include <linux/notifier.h>
+#include <linux/writeback.h>
+#include <linux/blkdev.h>
 #include "overlayfs.h"
 
 MODULE_AUTHOR("Miklos Szeredi <miklos@szeredi.hu>");
@@ -279,9 +282,13 @@ static int ovl_sync_fs(struct super_block *sb, int wait)
 
 	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);
+	if (upper_sb->s_op->sync_fs) {
+		down_read(&upper_sb->s_umount);
+		ret = upper_sb->s_op->sync_fs(upper_sb, wait);
+		if (!ret)
+			ret = sync_blockdev(upper_sb->s_bdev);
+		up_read(&upper_sb->s_umount);
+	}
 
 	return ret;
 }
@@ -400,11 +407,47 @@ void ovl_evict_inode(struct inode *inode)
 	clear_inode(inode);
 }
 
+int ovl_write_inode(struct inode *inode, struct writeback_control *wbc)
+{
+	struct ovl_fs *ofs = inode->i_sb->s_fs_info;
+	struct super_block *upper_sb = ovl_upper_mnt(ofs)->mnt_sb;
+	struct inode *upper_inode = ovl_inode_upper(inode);
+	struct writeback_control upper_wbc = {
+		.nr_to_write		= LONG_MAX,
+		.sync_mode              = WB_SYNC_ALL,
+		.tagged_writepages	= wbc->tagged_writepages,
+		.for_kupdate		= wbc->for_kupdate,
+		.for_background		= wbc->for_background,
+		.for_sync		= 0,
+		.range_cyclic		= wbc->range_cyclic,
+		.range_start		= wbc->range_start,
+		.range_end		= wbc->range_end,
+	};
+
+	if (!upper_sb->s_op->write_inode || !upper_inode)
+		return 0;
+	return upper_sb->s_op->write_inode(upper_inode, &upper_wbc);
+}
+
+int ovl_drop_inode(struct inode *inode)
+{
+	struct inode *upper_inode;
+
+	upper_inode = ovl_inode_upper(inode);
+	if (!upper_inode)
+		return 1;
+	if (!(upper_inode->i_state & I_DIRTY_ALL))
+		return 1;
+
+	return generic_drop_inode(inode);
+}
+
 static const struct super_operations ovl_super_operations = {
 	.alloc_inode	= ovl_alloc_inode,
 	.free_inode	= ovl_free_inode,
 	.destroy_inode	= ovl_destroy_inode,
-	.drop_inode	= generic_delete_inode,
+	.drop_inode	= ovl_drop_inode,
+	.write_inode	= ovl_write_inode,
 	.evict_inode	= ovl_evict_inode,
 	.put_super	= ovl_put_super,
 	.sync_fs	= ovl_sync_fs,
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index bdcfe55..93d0493 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -958,8 +958,7 @@ int ovl_inode_dirty_notify(struct notifier_block *nb,
 	struct ovl_inode *oi = container_of(nb, struct ovl_inode, mark_dirty_nb);
 	int *flags = (int *)param;
 
-	// add later
-	//__mark_inode_dirty(&oi->vfs_inode, *flags);
+	__mark_inode_dirty(&oi->vfs_inode, *flags);
 	return NOTIFY_OK;
 }
 
-- 
1.8.3.1