[Bug]: Single file mounts fail intermittently.

[jglogan]

I have done the following

• I have searched the existing issues
• If possible, I've reproduced the issue using the 'main' branch of this project

Steps to reproduce

There is a problem in the virtualization framework where files with more than one hard link may not be accessible when mounted via virtiofs into a VM.

The problem would affect any such files in a virtiofs share, but it is particularly evident with our single-file mount method, where we create an isolated mount source directory on the host and create a link to the source file in that directory.

echo "Hello, world!" > hello.txt
container run -it --rm -v ${PWD}/hello.txt:/hello.txt alpine sh
cat hello.txt

Current behavior

Sometimes we see the expected behavior, but other times it's:

% container run -it --rm -v ${PWD}/hello.txt:/hello.txt alpine sh
Warning! Running debug build. Performance may be degraded.
/ # vi hello.txt 
/ # cat hello.txt
cat: can't open 'hello.txt': Permission denied
/ # 

Expected behavior

% container run -it --rm -v ${PWD}/hello.txt:/hello.txt alpine sh
Warning! Running debug build. Performance may be degraded.
/ # cat hello.txt 
Hello, world!
/ # 

Environment

- OS: 26
- Xcode: 26
- Container: main

Relevant log output

N/A

Code of Conduct

• I agree to follow this project's Code of Conduct

[jglogan]

Need a fix for apple/containerization#509 to resolve this issue, or a workaround:

• Copy file to isolated source to prevent mounting siblings, but this means writes to the mounted file won't be reflected on the host.
• Mount the parent directory into the VM, but this means the sibling files are mounted into the VM as well. This may be acceptable as the container should not be able to access the directory, only the bind mounted file.

[seven1240]

Need a fix for apple/containerization#509 to resolve this issue, or a workaround:

• Copy file to isolated source to prevent mounting siblings, but this means writes to the mounted file won't be reflected on the host.

Maybe just copy when :ro is set? most time single file mount would be useful to mount read-only a single for config (e.g. nginx.conf) instead of copy the whole /etc/nginx dir to the host.

[dcantah]

That can work @seven1240 and is a neat idea

[dcantah]

I think if we actually used the default capabilities set that other runtimes employed, I wouldn't be as opposed to sharing in the parent directory and bind mounting in the file

[jglogan]

Just need to pick up the next CZ tag with apple/containerization#665 now.