netdev - Re: [PATCH bpf-next 2/3] bpftool: match programs by name

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Message-ID: <20191213095659.2782ca57@cakuba.netronome.com>
Date:   Fri, 13 Dec 2019 09:56:59 -0800
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Paul Chaignon <paul.chaignon@...nge.com>
Cc:     bpf@...r.kernel.org, Quentin Monnet <quentin.monnet@...ronome.com>,
        paul.chaignon@...il.com, netdev@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>
Subject: Re: [PATCH bpf-next 2/3] bpftool: match programs by name

On Fri, 13 Dec 2019 13:40:38 +0100, Paul Chaignon wrote:
> > > @@ -176,7 +177,20 @@ prog_parse_fds(int *argc, char ***argv, int *fds)
> > >  		}
> > >  		NEXT_ARGP();
> > >  
> > > -		return prog_fd_by_tag(tag, fds);
> > > +		return prog_fd_by_nametag(tag, fds, true);
> > > +	} else if (is_prefix(**argv, "name")) {
> > > +		char *name;
> > > +
> > > +		NEXT_ARGP();
> > > +
> > > +		name = **argv;
> > > +		if (strlen(name) > BPF_OBJ_NAME_LEN - 1) {  
> > 
> > Is this needed? strncmp will simply never match, is it preferred to
> > hard error?  
> 
> I tried to follow the fail-early pattern of lookups by tag above.  

Right although tag does a scanf and if we didn't scan all letters 
we'd use uninit memory.

> I do like that there's a different error message for a longer than
> expected name.  Since libbpf silently truncates names, typing a
> longer name is not uncommon.

Ugh, I didn't realize libbpf truncates names. Okay, let's keep the
error for now so we can switch to truncation if users complain.