fix a Hook Args Usage

[wangkirin]

When I try to use prestart hooks , I found a bug about hook args
If I add folllowing contents in runtime.json

"prestart":[ {
                "path": "/bin/bash",
                "args": ["-c","\"ls\""]
            }
            ],

runc terminated and return an error , but if I change the args to

"prestart":[ {
                "path": "/bin/bash",
                "args": ["test","-c","\"ls\""]
            }
            ],

I can get the list of files from standouput, even I change test to any other string such as adfafadsf, it also works, that means the first argument is useless

I think this problem is caused by the Cmd struct of golang , in Godocs, it says [1]
Args holds command line arguments, including the command as Args[0].
so I make a new string slice and insert a "" string in front of current Args before cmd.Runto slove that

[1] https://golang.org/pkg/os/exec/#Cmd
Signed-off-by: Wang Qilin wangqilin2@huawei.com

[hqhq]

No it's not a bug.

// Args holds command line arguments, including the command as Args[0].
// If the Args field is empty or nil, Run uses {Path}.
//
// In typical use, both Path and Args are set by calling Command.
Args []string

So the typical way you set prestart should be like:

"prestart":[ {
                "path": "/bin/bash",
                "args": ["/bin/bash", "-c", "\"ls\""]
            }
            ],

Thought it's not the only way that can work.

[wangkirin]

@hqhq , thank you for your review, maybe we can't really call it a bug and I have already fix it :)
I think in specs , there is no statment that if we set Args ,we should set the first argument the same with path, and the example given by specs is like

 "poststop": [
            {
                "path": "/usr/sbin/cleanup.sh",
                "args": ["-f"]
            }
        ]

so I think we can modify this

[hqhq]

@wangkirin Yeah, I didn't notice the specs examples, by intuition I think it should be the same as golang packages, I opened a PR opencontainers/runtime-spec#255 , let's see how that works.

[mrunalp]

This is working as intended as @hqhq pointed out.