netdev - Re: [PATCH bpf-next] tools: bpftool: add support for reporting the effective cgroup progs

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Message-ID: <20190730140040.7a357b19@cakuba.netronome.com>
Date:   Tue, 30 Jul 2019 14:00:40 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Takshak Chahande <ctakshak@...com>
Cc:     "alexei.starovoitov@...il.com" <alexei.starovoitov@...il.com>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "oss-drivers@...ronome.com" <oss-drivers@...ronome.com>,
        Kernel Team <Kernel-team@...com>,
        Quentin Monnet <quentin.monnet@...ronome.com>
Subject: Re: [PATCH bpf-next] tools: bpftool: add support for reporting the
 effective cgroup progs

On Tue, 30 Jul 2019 18:04:53 +0000, Takshak Chahande wrote:
> Jakub Kicinski <jakub.kicinski@...ronome.com> wrote on Mon [2019-Jul-29 14:35:38 -0700]:
> > @@ -158,20 +161,30 @@ static int show_attached_bpf_progs(int cgroup_fd, enum bpf_attach_type type,
> >  static int do_show(int argc, char **argv)
> >  {
> >  	enum bpf_attach_type type;
> > +	const char *path;
> >  	int cgroup_fd;
> >  	int ret = -1;
> >  
> > -	if (argc < 1) {
> > -		p_err("too few parameters for cgroup show");
> > -		goto exit;
> > -	} else if (argc > 1) {
> > -		p_err("too many parameters for cgroup show");
> > -		goto exit;
> > +	query_flags = 0;
> > +
> > +	if (!REQ_ARGS(1))
> > +		return -1;
> > +	path = GET_ARG();
> > +
> > +	while (argc) {
> > +		if (is_prefix(*argv, "effective")) {
> > +			query_flags |= BPF_F_QUERY_EFFECTIVE;
> > +			NEXT_ARG();
> > +		} else {
> > +			p_err("expected no more arguments, 'effective', got: '%s'?",
> > +			      *argv);
> > +			return -1;
> > +		}
> >  	}  
> This while loop will allow multiple 'effective' keywords in the argument
> unnecessarily. IMO, we should strictly restrict only for single
> occurance of 'effective' word.

It's kind of the way all bpftool works to date :(

But perhaps not checking is worse than inconsistency? Okay, let's fix
this up.

> > -	cgroup_fd = open(argv[0], O_RDONLY);
> > +	cgroup_fd = open(path, O_RDONLY);
> >  	if (cgroup_fd < 0) {
> > -		p_err("can't open cgroup %s", argv[0]);
> > +		p_err("can't open cgroup %s", path);
> >  		goto exit;
> >  	}
> >  
> > @@ -297,23 +310,29 @@ static int do_show_tree(int argc, char **argv)
> >  	char *cgroup_root;
> >  	int ret;
> >  
> > -	switch (argc) {
> > -	case 0:
> > +	query_flags = 0;
> > +
> > +	if (!argc) {
> >  		cgroup_root = find_cgroup_root();
> >  		if (!cgroup_root) {
> >  			p_err("cgroup v2 isn't mounted");
> >  			return -1;
> >  		}
> > -		break;
> > -	case 1:
> > -		cgroup_root = argv[0];
> > -		break;
> > -	default:
> > -		p_err("too many parameters for cgroup tree");
> > -		return -1;
> > +	} else {
> > +		cgroup_root = GET_ARG();
> > +
> > +		while (argc) {
> > +			if (is_prefix(*argv, "effective")) {
> > +				query_flags |= BPF_F_QUERY_EFFECTIVE;
> > +				NEXT_ARG();  
> 
> NEXT_ARG() does update argc value; that means after this outer if/else we need 
> to know how argc has become 0 (through which path) before freeing up `cgroup_root` allocated
> memory later at the end of this function.

Good catch!

> > +			} else {
> > +				p_err("expected no more arguments, 'effective', got: '%s'?",
> > +				      *argv);
> > +				return -1;
> > +			}
> > +		}
> >  	}  
 
> Thanks for the patch. Apart from above two issues, patch looks good.

Thanks for the review.