cmd/netsetgo: Enforce pid argument

[marcosps]

If we call netsetgo without arguments, it returns an error:
ERROR - no such process

It fails because Veth.MoveToNetworkNamespace calls
netlink.LinkSetNsPid, which needs a pid that belongs to another netns in
order to set a veth interface inside the new netns.

So, before doing any setup, check if a pid was passed as argument of
netsetgo.

Signed-off-by: Marcos Paulo de Souza marcos.souza.org@gmail.com

[teddyking]

Thanks @marcosps!

Any chance you'd be able to add a test for this as well?
Maybe something to https://github.com/teddyking/netsetgo/blob/master/integration_test.go along the lines of

Context("when an invalid pid is provided", func() { 
    It("exits -1", func() {  
        ... 
    })
})

[marcosps]

Sure, will try to do so in a few hours!

[marcosps]

@teddyking I'm struggling to install this concourse ci in my Ubuntu, but don't worry, it won't take the whole weekend (that's what I expect at least...)

[teddyking]

Oh yeah that can be a bit tricky. You should also be able to just run the tests by installing ginkgo and running ginkgo -r from the root of the netsetgo repo. Although note that you'll need to be the root user and this will actually add/remove network interfaces from your machine (should be fairly safe but just FYI).

No worries if you can't get it working, I can add a test in later.

[marcosps]

@teddyking tricky yes, but I made it work :)

I hope this now fulfills your expectations!

[teddyking]

Awesome, looks good to me.

Thanks!
Ed