Hope support overlayfs upper layer on juicefs

[wuyongzhi]

when i create overlay fs with juicefs as upper layer, i can not create overlay fs, it got a error:

the command:

# mount -t overlay o1 -o lowerdir=jfs/exercises/001,upperdir=jfs/user/001,workdir=workspaces/001/work workspaces/001/merged

output:

mount: /opt/workspaces/001/merged: wrong fs type, bad option, bad superblock on o1, missing codepage or helper program, or other error

What would you like to be added:
create overlay fs with juicefs as upper layer,

Why is this needed:

[davies]

Based on: https://www.kernel.org/doc/html/latest/filesystems/overlayfs.html

The upper filesystem will normally be writable and if it is it must support the creation of trusted.* and/or user.* extended attributes, and must provide valid d_type in readdir responses

You need to mount JuiceFS with --enable-xattr to use it as upper layer.

[destitutus]

Hello

I tried to use overlayfs on JuiceFS too. I added --enable-xattr flag as it was suggested, unfortunately I got the same error

Ubuntu 22.04 error and dmesg logs

sudo mount -t overlay -o userxattr -o "upperdir=/jfs/objfs/upperdir,lowerdir=/jfs/objfs/lowerdir,workdir=/jfs/objfs/workdir" overlay /jfs/objfs/dir
mount: /jfs/objfs/dir: wrong fs type, bad option, bad superblock on overlay, missing codepage or helper program, or other error.

[220515.137604] overlayfs: upper fs does not support tmpfile.
[220515.492296] overlayfs: upper fs does not support RENAME_WHITEOUT.
[220515.611151] overlayfs: upper fs missing required features.

Ubuntu 18.04

sudo mount -t overlay -o "upperdir=/jfs/objfs/upperdir,lowerdir=/jfs/objfs/lowerdir,workdir=/jfs/objfs/workdir" none /jfs/objfs/dir
mount: /jfs/objfs/dir: wrong fs type, bad option, bad superblock on none, missing codepage or helper program, or other error.

[3190825.210190] overlayfs: filesystem on '/jfs/objfs/upperdir' not supported as upperdir

./juicefs version
JuiceFS version 4.7.5 (2022-07-06 39f5d3e)

[SandyXSD]

JuiceFS is based on FUSE, which is not allowed to be the upper layer of overlayfs, details: #2365

[1247862674]

Is it supported now?

[zhijian-pro]

We recently supported O_TMPFILE falg, #5309, but whether overlayfs has been fully support we didn't test, you can compile the main test, If there's a problem, we can discuss it