Comment 20 for bug 1824407

I was thinking of a more generalized overlayfs solution that detects if file systems don't initialize the superblock uuid and overlayfs improvises by generating the internal overlayfs uuid, something like:

diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
index 698d112bdb17..da3faaf68d69 100644
--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -248,6 +248,7 @@ struct ovl_fh *ovl_encode_real_fh(struct dentry *real, bool is_upper)
        void *buf;
        int buflen = MAX_HANDLE_SZ;
        uuid_t *uuid = &real->d_sb->s_uuid;
+ static const uuid_t z_uuid;

        buf = kmalloc(buflen, GFP_KERNEL);
        if (!buf)
@@ -289,7 +290,22 @@ struct ovl_fh *ovl_encode_real_fh(struct dentry *real, bool is_upper)
        if (is_upper)
                fh->flags |= OVL_FH_FLAG_PATH_UPPER;
        fh->len = fh_len;
- fh->uuid = *uuid;
+
+ if (uuid_equal(uuid, &z_uuid)) {
+ struct super_block *sb = real->d_sb;
+ u16 hash;
+
+ pr_warn("ovl_encode_real_fh: ZERO UUID, generating one from superblock\n");
+
+ memcpy(&fh->uuid.b[0], &sb->s_magic, 8);
+ memcpy(&fh->uuid.b[8], &sb->s_dev, 6);
+ hash = ((long)sb ^ (long)sb->s_fs_info) >> 12;
+ memcpy(&fh->uuid.b[14], &hash, 2);
+ } else {
+ fh->uuid = *uuid;
+ }
+