cp fails to detect readonly mount and fallback into tar error

[apostasie]

Description

This

https://github.com/containerd/nerdctl/blob/main/pkg/containerutil/cp_linux.go#L305

should surface error: "mount point %s is marked read-only"

This is two fold:

• error message
• more importantly, the logic in getContainerMountInfo seems to be broken

Steps to reproduce the issue

touch something
nerdctl volume create foo
nerdctl run -d --name testro -v foo:/bar:ro debian sleep Inf
nerdctl cp something testro:/bar

Describe the results you received and expected

Received:

/usr/bin/tar: something: Cannot open: Read-only file system
/usr/bin/tar: Exiting with failure status due to previous errors
FATA[0000] could not find container: testro, with error: failed to wait [nsenter -t 1958627 -U --preserve-credentials -- /usr/bin/tar -x -f -]: exit status 2

Expected:

mount point %s is marked read-only

What version of nerdctl are you using?

main

Are you using a variant of nerdctl? (e.g., Rancher Desktop)

None

Host information

Am I missing something or doing something wrong?

[apostasie]

Actually, the method is never called (on a running container), because we have a root already (/proc/1958627/root).