[Request]: Support bind mounting the same directory multiple times in the container

[justinyaodu]

Feature or enhancement request details

If I mount one directory into a container, it works fine:

container run -it --rm --mount type=bind,src=$HOME,dst=/home-ro,ro debian:unstable bash

But if I try to mount the same directory twice, it fails:

container run -it --rm --mount type=bind,src=$HOME,dst=/home-rw --mount type=bind,src=$HOME,dst=/home-ro,ro debian:unstable bash
Error: unknown: "Error Domain=VZErrorDomain Code=2 "More than one Virtio File System device uses the tag “04131abe9006686b4bfe17357444d13e2622”." UserInfo={NSLocalizedFailure=Invalid virtual machine configuration., NSLocalizedFailureReason=More than one Virtio File System device uses the tag “04131abe9006686b4bfe17357444d13e2622”.}"

Admittedly, I don't have a compelling need for this, but the limitation feels a bit arbitrary and didn't see any mention of it elsewhere. I figured I could post an issue in case it's a simple fix. Thanks!

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[egernst]

I honestly can't think of a scenario where a user would want to do this. We can look into this, but it'll be a lower priority on our end.

At this point, you have CAP_SYS_ADMIN, so you should be able to work around by doing your own bind mount of original to a second path, as well.

[dcantah]

To be fair, this shouldn't be all too bad to fix over in the containerization library (where this error is originating from). Let me see over the next 30 minutes or so

[dcantah]

apple/containerization#243 this should fix it

[mislav]

I honestly can't think of a scenario where a user would want to do this. We can look into this, but it'll be a lower priority on our end.

I just came across this error in the wild.

I was trying to port the xgo tool to be able to use container instead of docker on macOS. xgo is a command-line tool and a container image that facilitates cross-compiling Go projects, and what it eventually does is runs docker run ... ghcr.io/techknowlogick/xgo:latest with a list of arguments that is programmatically assembled at run time. When I changed this to use container run, the invocation failed with:

Error: internalError: "failed to bootstrap container" (cause: "internalError: "failed to bootstrap container 8e3ea6b8-6c58-4beb-b1a6-8b8c1291035a (cause: "unknown: "Error Domain=VZErrorDomain Code=2 "More than one Virtio File System device uses the tag “a31b3874d20fcfa2a80edff450afefe5cff6”." UserInfo={NSLocalizedFailure=Invalid virtual machine configuration., NSLocalizedFailureReason=More than one Virtio File System device uses the tag “a31b3874d20fcfa2a80edff450afefe5cff6”.}"")"")

There are multiple volumes mounted into this container, and because the directory paths come from user input, it's entirely possible that the same directory is mounted into multiple locations inside the container: https://github.com/techknowlogick/xgo/blob/618e96d285f302ba26d8e9c276293edb73345a44/xgo.go#L461-L463

After I worked around duplicate mounts by using different directories, container run … worked splendidly, so this was really the only incompatibility I could find when switching from docker to container.

Thank you @dcantah for the PR that enables this, and I hope it gets reviewed eventually!

[jglogan]

Closed by apple/containerization#522.