On Mon, Sep 4, 2023 at 10:47 AM Jingbo Xu <jefflexu@xxxxxxxxxxxxxxxxx> wrote: > > 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. > The case of whiteouts creates by overlayfs itself was reported by zhangyi and handled by this patchs set: https://lore.kernel.org/linux-unionfs/1509486350-21362-1-git-send-email-amir73il@xxxxxxxxx/ so you could say that the problem is due to the way that you created those layers. There is a simple workaround for you though: mkdir -p /mnt/lower1/dir /mnt/lower2/dir Making 'dir' a merge dir avoids the problem. Not sure if that helps. The alternative way is: setfattr -n "trusted.overlay.origin" /mnt/lower1/dir Thanks, Amir.
