Hi, all, I found an issue may be related to overlayfs on the latest master branch [1] when I'm developing tarfs mode for erofs-utils [2], which converts and merges tar layers into one merged erofs image with overlayfs-like model. The issue is that, the whiteout from lowerdir may still shows up in the merged directory. Though this issue is initially found with erofs, it can also be reproduced with ext4. Following is a simple reproducer with ext4. ``` mkdir -p /mnt/lower1/dir /mnt/lower2 mknod /mnt/lower1/file1 c 0 0 mknod /mnt/lower1/dir/file2 c 0 0 mount -t overlay none -olowerdir=/mnt/lower1:/mnt/lower2 /mnt2 # ls -l /mnt2/ total 4 drwxr-xr-x 2 root root 4096 Sep 4 14:40 dir # ls -l /mnt2/dir ls: cannot access /mnt2/dir/file2: No such file or directory total 0 c????????? ? ? ? ? ? file2 ``` It seems that this issue is relevant to whether the parent directory of the whiteout is a merged directory or not. In the above example, file1 is hidden from the merged directory as expected (with its parent directory '/' a merged directory), while file2 shows up unexpectedly (with its parent directory '/dir' from lowerdir). I also noticed that this issue doesn't exist if the whiteout is created by overlayfs itself rather than handcrafted with mknod like: ``` mkdir -p /mnt/lower/dir /mnt/upper /mnt/work touch /mnt/lower/file1 touch /mnt/lower/dir/file2 mount -t overlay none -olowerdir=/mnt/lower,upperdir=/mnt/upper,workdir=/mnt/work /mnt1 rm /mnt1/file1 rm /mnt1/dir/file2 umount /mnt1 mount -t overlay -olowerdir=/mnt/upper:/mnt/lower none /mnt2 # ls -l /mnt2/ total 8 drwxr-xr-x 1 root root 4096 Sep 4 15:45 dir # ls -l /mnt2/dir/ total 0 ``` I'm not sure if it's a known issue or not, or due to my mishandling. Appreciate if you could shed a light on this. [1] git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git [2] https://lore.kernel.org/all/20230901094706.27539-1-jefflexu@xxxxxxxxxxxxxxxxx/ -- Thanks, Jingbo
