Stale file handle in the guest after changing file on the host

[Romeus]

Prerequisites

Vng is built from source and installed in a virtual environment:

(virtme) hedin@laptop:~/prj$ vng --version
virtme-ng 1.31+5.g1da4504

Host OS version:
hedin@laptop:~$ cat /etc/os-release
PRETTY_NAME="Ubuntu 24.04.1 LTS"
NAME="Ubuntu"
VERSION_ID="24.04"
VERSION="24.04.1 LTS (Noble Numbat)"
VERSION_CODENAME=noble
ID=ubuntu
ID_LIKE=debian
HOME_URL="https://www.ubuntu.com/"
SUPPORT_URL="https://help.ubuntu.com/"
BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
UBUNTU_CODENAME=noble
LOGO=ubuntu-logo

Reproducer

1. Build the latest linux-next and run it:
   (virtme) hedin@laptop:~/prj$ vng -r kernel_builds/linux-next-virtme/
   _ _
   __ ()_ | | _ __ ___ ___ _ __ __ _
   \ \ / / | | | _ _ \ / _ ____| _ \ / _ |
   \ V /| | | | || | | | | | /| | | | (| |
   _/ ||| _|| || |_|_| || ||__ |
   |___/
   kernel version: 6.12.0-rc3-next-20241018-virtme x86_64
   (CTRL+d to exit)

2. Create a file on the host:
   hedin@laptop:~$ echo "123" > test.txt

3. Check it on the guest:
   hedin@virtme-ng:~$ cat test.txt
   123

4. Modify it on the host by adding something:
   hedin@laptop:~$ vim test.txt

5. Check the changes in the guest:
   hedin@virtme-ng:~$ cat test.txt
   cat: test.txt: Stale file handle

6. Close the editor in the host and check file on the guest one more time:
   hedin@virtme-ng:~$ cat test.txt
   cat: test.txt: Stale file handle

7. List files in the guest:
   hedin@virtme-ng:~$ ls
   ls: cannot access 'test.txt': Stale file handle

8. Remove the file from the host:
   hedin@laptop:~$ rm test.txt

9. The error in the guest disappeared

[arighi]

Interesting, this looks like a virtiofs bug, if you run vng --force-9p it doesn't seem to happen. I'll investigate a bit to see if it's a known bug.

[Romeus]

I checked it using:
vng --force-9p -r kernel_builds/linux-next-virtme/
and the issue disappeared. So, I guess that you are right - this is virtiofs-related bug.

[marcosps]

I've seen this issue for quite some time already but I though it was related to some issue I'm my distro. Good to know this problem doesn't happen only on my machine :)