[PATCH 05/10] ovl: setup overlayfs' private bdi

[Josef Bacik]

From: Chengguang Xu <charliecgxu@xxxxxxxxxxx>

Setup overlayfs' private bdi so that we can collect overlayfs' own dirty
inodes.

Signed-off-by: Chengguang Xu <charliecgxu@xxxxxxxxxxx>
[josef: only for an overlay which is going to have dirty inodes, rebased]
Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
---
 fs/overlayfs/overlayfs.h | 13 +++++++++++++
 fs/overlayfs/super.c     |  7 +++++++
 2 files changed, 20 insertions(+)

diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 92da556598da..218f646b82b9 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -663,6 +663,19 @@ static inline bool ovl_should_sync(struct ovl_fs *ofs)
 	return ofs->config.fsync_mode != OVL_FSYNC_VOLATILE;
 }
 
+/*
+ * Does this overlay keep track of the upper inodes which are changed through
+ * it, to sync only those?  It knows where it wrote data.  It does not know of
+ * every inode which the upper filesystem dirtied on its behalf, so that has to
+ * be a filesystem where ->sync_fs() takes care of all metadata.  With any other
+ * one syncfs() and unmount sync the whole upper filesystem.
+ */
+static inline bool ovl_tracks_dirty(struct ovl_fs *ofs)
+{
+	return ovl_upper_mnt(ofs) && ovl_should_sync(ofs) &&
+	       (ovl_upper_mnt(ofs)->mnt_sb->s_iflags & SB_I_OVL_USE_SYNC_FS);
+}
+
 static inline bool ovl_should_sync_metadata(struct ovl_fs *ofs)
 {
 	return ofs->config.fsync_mode == OVL_FSYNC_STRICT;
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 19b6d54c4500..d21e7cbb70c2 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -1455,6 +1455,13 @@ static int ovl_fill_super_creds(struct fs_context *fc, struct super_block *sb)
 		if (err)
 			return err;
 
+		/* Dirty overlay inodes need a writeback list to be on */
+		if (ovl_tracks_dirty(ofs)) {
+			err = super_setup_bdi(sb);
+			if (err)
+				return err;
+		}
+
 		upper_sb = ovl_upper_mnt(ofs)->mnt_sb;
 		if (!ovl_should_sync(ofs)) {
 			ofs->errseq = errseq_sample(&upper_sb->s_wb_err);

-- 
2.55.0