Add support for --preserve-fds to podman run

[eriksjolund]

Is this a BUG REPORT or FEATURE REQUEST? (leave only one on its own line)

/kind feature

Description
Summary: Add support for --preserve-fds=N to podman run, in the same way that the command-line option is supported in podman exec.

Example:
The command foobar (in the container localhost/example) reads input from the file descriptor 0 and the file descriptor 3.
My goal is is to run foobar and pass the file file1.txt as file descriptor 0 and the file file2.txt as file descriptor 3. (Both file1.txt and file2.txt are located on the host system)

It would be nice to be able to run

$ cat file1.txt | podman run --rm -i --preserve-fds=1 localhost/example foobar 3< file2.txt

but that is currently not possible. Instead I need to use podman exec, something like this:

$ ctr=$(podman run -d --rm localhost/example sleep 300)
$ cat file1.txt | podman exec -i --preserve-fds=1 $ctr foobar 3< file2.txt

More info:

$ echo $0
-bash
$ podman --version
podman version 1.9.2

[mheon]

Shouldn't be that difficult (the reason --preserve-fds is exec-only is that the original request was only for exec, there are no technical reasons it won't work with podman run). Unfortunately, most of the team is swamped with Podman 2.0 work at the moment, so I can't guarantee we'll get to this quickly; community PRs are always welcome, though!

[rhatdan]

@eriksjolund Feel like opening a PR?
@sujil02 @QiWang19 PTAL

[eriksjolund]

@rhatdan Up till now I've only been a Golang code reader and not a Golang code writer, so it would take a bit of an effort to do an PR. Unfortunately I have too little time right now.

[rhatdan]

No problem @eriksjolund, thanks for the issue.

I am always trying to encourage contributions. Anyone helping in OpenSource projects are appreciated.

[QiWang19]

@eriksjolund can you provide more details? what the uses case foobar command specifically running?

[eriksjolund]

@eriksjolund can you provide more details? what the uses case foobar command specifically running?

I wanted to create a command-line tool to demonstrate a C++ library. The command-line tool needs two input files.
I think a user without much experience of bind mounts and SELINUX security file contexts would find it convenient to be able to do:

cat file1.txt | podman run --rm -i --preserve-fds=1 localhost/example foobar 3< file2.txt

I see that the PR #6625 has been merged:
Thanks!

Is the feature available in any release?

Fedora 32

[erik@laptop ~]$ cat /etc/fedora-release 
Fedora release 32 (Thirty Two)
[erik@laptop ~]$ podman --version
podman version 2.0.2
[erik@laptop ~]$ podman run --help | grep preserve-fds
[erik@laptop ~]$ 

Centos 8

[erik@centos ~]$ cat /etc/centos-release
CentOS Linux release 8.2.2004 (Core) 
[erik@centos ~]$ podman --version
podman version 2.0.3
[erik@centos ~]$ podman run --help | grep preserve-fds
[erik@centos ~]$ rpm -qi podman
Name        : podman
Epoch       : 0
Version     : 2.0.3
Release     : 1.el8
Architecture: x86_64
Install Date: Thu 23 Jul 2020 11:56:28 PM CEST
Group       : Unspecified
Size        : 74267642
License     : ASL 2.0
Signature   : RSA/SHA256, Thu 23 Jul 2020 09:42:24 PM CEST, Key ID 4d64390375060aa4
Source RPM  : podman-2.0.3-1.el8.src.rpm
Build Date  : Thu 23 Jul 2020 09:41:48 PM CEST
Build Host  : cloud107
Relocations : (not relocatable)
Vendor      : obs://build.opensuse.org/devel:kubic
URL         : https://podman.io/
Summary     : Manage Pods, Containers and Container Images
Description :
podman (Pod Manager) is a fully featured container engine that is a simple
daemonless tool.  podman provides a Docker-CLI comparable command line that
eases the transition from other container engines and allows the management of
pods, containers and images.  Simply put: alias docker=podman.
Most podman commands can be run as a regular user, without requiring
additional privileges.

podman uses Buildah(1) internally to create container images.
Both tools share image (not container) storage, hence each can use or
manipulate images (but not containers) created by the other.

Manage Pods, Containers and Container Images
podman is a simple management tool for pods, containers and images
[erik@centos ~]$ 

[eriksjolund]

podman run --preserve-fds might become available in v2.1.0 according to
#6909 (comment)