--tmpfs defaults are not compatible with docker

[computator]

/kind bug

The --tmpfs option (and probably --mount too) defaults to 64MB of space, vs docker's default size is unlimited according to this documentation of tmpfs-size.

In addition, Docker's --tmpfs doesn't allow any options, but podman's has several. I'm not too concerned about this one though since the tmpfs syntax for podman is a superset of Docker's.

Output of podman version:

podman version 1.4.4

[rhatdan]

@ashley-cui PTAL, just change the --tmpfs to not be confined to 64k.

[rhatdan]

Or @computator if you want to take a stab at fixing it. PRs welcome...

[ashley-cui]

@ashley-cui PTAL, just change the --tmpfs to not be confined to 64k.

@rhatdan should I just remove the default value for --tmpfs? How would I test this?

[ashley-cui]

@rhatdan When the --tmpfs flag is used in docker, no defaults are set. However, in podman, it automatically sets various defaults:

$docker create --name test --tmpfs /a alpine
docker inspect test 
...
"Tmpfs": {
    "/a": ""
}

$podman create --name test --tmpfs /a alpine
podman inspect test 
...
"Tmpfs": {
                "/a": "noexec,nosuid,nodev,rw,size=65536k,rprivate,tmpcopyup"
            }

Should this also be fixed? I'm not really sure where the size and other defaults are used later in control flow, so I'm wary of how to manipulate it.

[mheon]

Related: #3803

We set these defaults largely for security. I think that 65MB is a safe default that can be increased if required.

[rhatdan]

I would remove the 65mb, since this is still controlled by the cgroup. The tmpfs space is < 50% of all available Memory for all tmpfs in the contianer (Memory cgroup).
The other flags should stay. I don't see a problem with nodev, nosuid. Perhaps we should eliminate noexec.