linux-kernel - Re: [PATCH bpf-next v1] bpf, iter: clean up bpf_seq

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Date:   Tue, 2 Aug 2022 13:14:36 +0200
From:   Jiri Olsa <olsajiri@...il.com>
To:     Hao Luo <haoluo@...gle.com>
Cc:     linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Stanislav Fomichev <sdf@...gle.com>
Subject: Re: [PATCH bpf-next v1] bpf, iter: clean up bpf_seq_read().

On Mon, Aug 01, 2022 at 01:50:39PM -0700, Hao Luo wrote:

SNIP

> +static int do_seq_show(struct seq_file *seq, void *p, size_t offs)
> +{
> +	int err;
> +
> +	WARN_ON(IS_ERR_OR_NULL(p));
> +
> +	err = seq->op->show(seq, p);
> +	if (err > 0) {
> +		/* object is skipped, decrease seq_num, so next
> +		 * valid object can reuse the same seq_num.
> +		 */
> +		bpf_iter_dec_seq_num(seq);
> +		seq->count = offs;
> +		return err;
> +	}
> +
> +	if (err < 0 || seq_has_overflowed(seq)) {
> +		seq->count = offs;
> +		return err ? err : -E2BIG;
> +	}
> +
> +	/* err == 0 and no overflow */
> +	return 0;
> +}
> +
> +/* do_seq_stop, stops at the given object 'p'. 'p' could be an ERR or NULL. If
> + * 'p' is an ERR or there was an overflow, reset seq->count to 'offs' and
> + * returns error. Returns 0 otherwise.
> + */
> +static int do_seq_stop(struct seq_file *seq, void *p, size_t offs)
> +{
> +	if (IS_ERR(p)) {
> +		seq->op->stop(seq, NULL);
> +		seq->count = offs;

should we set seq->count to 0 in case of error?

jirka

> +		return PTR_ERR(p);
> +	}
> +
> +	seq->op->stop(seq, p);
> +	if (!p) {
> +		if (!seq_has_overflowed(seq)) {
> +			bpf_iter_done_stop(seq);
> +		} else {
> +			seq->count = offs;
> +			if (offs == 0)
> +				return -E2BIG;
> +		}
> +	}
> +	return 0;
> +}
> +
>  /* maximum visited objects before bailing out */
>  #define MAX_ITER_OBJECTS	1000000
>  

SNIP