Re: [PATCH 8/8] Allow pasta to take a command to execute

[Stefano Brivio <sbrivio@redhat.com>]

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On Fri, 26 Aug 2022 14:58:39 +1000
David Gibson <david(a)gibson.dropbear.id.au> wrote:

> When not given an existing PID or network namspace to attach to, pasta
> spawns a shell.  Most commands which can spawn a shell in an altered
> environment can also run other commands in that same environment, which can
> be useful in automation.
> 
> Allow pasta to do the same thing; it can be given an arbitrary command to
> run in the network and user namespace which pasta creates.  If neither a
> command nor an existing PID or netns to attach to is given, continue to
> spawn a default shell, as before.
> 
> Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au>
> ---
>  conf.c  | 27 ++++++++++++++++++---------
>  passt.1 | 14 +++++++++-----
>  pasta.c | 33 +++++++++++++++++++++++----------
>  pasta.h |  2 +-
>  4 files changed, 51 insertions(+), 25 deletions(-)
> 
> diff --git a/conf.c b/conf.c
> index 2a18124..162c2dd 100644
> --- a/conf.c
> +++ b/conf.c
> @@ -550,7 +550,8 @@ static int conf_ns_pid(char *userns, char *netns, const char *arg)
>  		return 0;
>  	}
>  
> -	return -EINVAL;
> +	/* Not a PID, later code will treat as a command */
> +	return 0;
>  }
>  
>  /**
> @@ -1480,14 +1481,18 @@ void conf(struct ctx *c, int argc, char **argv)
>  
>  	check_root(c);
>  
> -	if (c->mode == MODE_PASTA && optind + 1 == argc) {
> -		ret = conf_ns_pid(userns, netns, argv[optind]);
> -		if (ret < 0)
> +	if (c->mode == MODE_PASTA) {
> +		if (*netns && optind != argc) {
> +			err("Both --netns and PID or command given");
>  			usage(argv[0]);
> -	} else if (c->mode == MODE_PASTA && *userns
> -		   && !*netns && optind == argc) {
> -		err("--userns requires --netns or PID");
> -		usage(argv[0]);
> +		} else if (optind + 1 == argc) {
> +			ret = conf_ns_pid(userns, netns, argv[optind]);
> +			if (ret < 0)
> +				usage(argv[0]);
> +		} else if (*userns && !*netns && optind == argc) {
> +			err("--userns requires --netns or PID");
> +			usage(argv[0]);
> +		}
>  	} else if (optind != argc) {
>  		usage(argv[0]);
>  	}
>
> [...]

I haven't really looked into this yet, but I guess we should now
handle getopts return codes a bit differently, because this works:

  $ ./pasta --config-net -- sh -c 'sleep 1; ip li sh'
  1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
      link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
  2: enp9s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 65520 qdisc pfifo_fast state UNKNOWN mode DEFAULT group default qlen 1000
      link/ether aa:3e:39:5f:c6:15 brd ff:ff:ff:ff:ff:ff

while this doesn't:

  $ ./pasta --config-net sh -c 'sleep 1; ip li sh'
  ./pasta: invalid option -- 'c'
  [...]

despite the fact that there's no ambiguity.

-- 
Stefano