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From:   Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= <toke@kernel.org>
To:     Zhengchao Shao <shaozhengchao@huawei.com>, bpf@vger.kernel.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        ast@kernel.org, daniel@iogearbox.net, davem@davemloft.net,
        kuba@kernel.org, hawk@kernel.org, john.fastabend@gmail.com,
        andrii@kernel.org, kafai@fb.com, songliubraving@fb.com, yhs@fb.com,
        kpsingh@kernel.org
Cc:     weiyongjun1@huawei.com, shaozhengchao@huawei.com,
        yuehaibing@huawei.com
Subject: Re: [PATCH v5,bpf-next] samples/bpf: check detach prog exist or not
 in xdp_fwd
In-Reply-To: <20220602011915.264431-1-shaozhengchao@huawei.com>
References: <20220602011915.264431-1-shaozhengchao@huawei.com>
Date:   Thu, 02 Jun 2022 10:55:20 +0200
Message-ID: <87v8tjsavb.fsf@toke.dk>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

Zhengchao Shao <shaozhengchao@huawei.com> writes:

> Before detach the prog, we should check detach prog exist or not.
>
> Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>

You missed one 'return errno', see below:

> ---
>  samples/bpf/xdp_fwd_user.c | 55 +++++++++++++++++++++++++++++++++-----
>  1 file changed, 49 insertions(+), 6 deletions(-)
>
> diff --git a/samples/bpf/xdp_fwd_user.c b/samples/bpf/xdp_fwd_user.c
> index 1828487bae9a..d321e6aa9364 100644
> --- a/samples/bpf/xdp_fwd_user.c
> +++ b/samples/bpf/xdp_fwd_user.c
> @@ -47,17 +47,60 @@ static int do_attach(int idx, int prog_fd, int map_fd, const char *name)
>  	return err;
>  }
>  
> -static int do_detach(int idx, const char *name)
> +static int do_detach(int ifindex, const char *ifname, const char *app_name)
>  {
> -	int err;
> +	LIBBPF_OPTS(bpf_xdp_attach_opts, opts);
> +	struct bpf_prog_info prog_info = {};
> +	char prog_name[BPF_OBJ_NAME_LEN];
> +	__u32 info_len, curr_prog_id;
> +	int prog_fd;
> +	int err = 1;
> +
> +	if (bpf_xdp_query_id(ifindex, xdp_flags, &curr_prog_id)) {
> +		printf("ERROR: bpf_xdp_query_id failed (%s)\n",
> +		       strerror(errno));
> +		return err;
> +	}
>  
> -	err = bpf_xdp_detach(idx, xdp_flags, NULL);
> -	if (err < 0)
> -		printf("ERROR: failed to detach program from %s\n", name);
> +	if (!curr_prog_id) {
> +		printf("ERROR: flags(0x%x) xdp prog is not attached to %s\n",
> +		       xdp_flags, ifname);
> +		return err;
> +	}
>  
> +	info_len = sizeof(prog_info);
> +	prog_fd = bpf_prog_get_fd_by_id(curr_prog_id);
> +	if (prog_fd < 0) {
> +		printf("ERROR: bpf_prog_get_fd_by_id failed (%s)\n",
> +		       strerror(errno));
> +		return errno;

This should just be 'return prog_fd' to propagate the error...

-Toke