netdev - Re: [PATCH v9 bpf-next 13/14] selftests/bpf: Add test for d

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Message-ID: <20200805180034.GE319954@krava>
Date:   Wed, 5 Aug 2020 20:00:34 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Jiri Olsa <jolsa@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andriin@...com>,
        Wenbo Zhang <ethercflow@...il.com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Martin KaFai Lau <kafai@...com>,
        David Miller <davem@...hat.com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Brendan Gregg <bgregg@...flix.com>,
        Florent Revest <revest@...omium.org>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH v9 bpf-next 13/14] selftests/bpf: Add test for d_path
 helper

On Tue, Aug 04, 2020 at 11:40:05PM -0700, Andrii Nakryiko wrote:

SNIP

> > +SEC("fentry/vfs_getattr")
> > +int BPF_PROG(prog_stat, struct path *path, struct kstat *stat,
> > +            __u32 request_mask, unsigned int query_flags)
> > +{
> > +       pid_t pid = bpf_get_current_pid_tgid() >> 32;
> > +       int ret;
> > +
> > +       if (pid != my_pid)
> > +               return 0;
> > +
> > +       if (cnt_stat >= MAX_FILES)
> > +               return 0;
> > +       ret = bpf_d_path(path, paths_stat[cnt_stat], MAX_PATH_LEN);
> > +
> > +       /* We need to recheck cnt_stat for verifier. */
> > +       if (cnt_stat >= MAX_FILES)
> > +               return 0;
> > +       rets_stat[cnt_stat] = ret;
> > +
> > +       cnt_stat++;
> > +       return 0;
> > +}
> > +
> > +SEC("fentry/filp_close")
> > +int BPF_PROG(prog_close, struct file *file, void *id)
> > +{
> > +       pid_t pid = bpf_get_current_pid_tgid() >> 32;
> > +       int ret;
> > +
> > +       if (pid != my_pid)
> > +               return 0;
> > +
> > +       if (cnt_close >= MAX_FILES)
> > +               return 0;
> > +       ret = bpf_d_path(&file->f_path,
> > +                        paths_close[cnt_close], MAX_PATH_LEN);
> > +
> > +       /* We need to recheck cnt_stat for verifier. */
> 
> you need to do it because you are re-reading a global variable; if you
> stored cnt_close in a local variable, then did >= MAX_FILES check
> once, you probably could have avoided this duplication. Same for
> another instance above.

I see, nice.. I'll update both comments

thanks,
jirka