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Date:   Sun, 9 Jul 2023 11:44:42 +0800
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Subject: Re: [PATCH bpf-next v2 0/2] bpf: Introduce user log
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To:     Daniel Xu <dxu@dxuuu.xyz>
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References: <20230708040750.72570-1-hffilwlqm@gmail.com>
 <v76ytdfdf2sqhdufkqxzsuznandia3x4l4iyghpirxkzytngxq@uttzaebbmdjb>
From:   Leon Hwang <hffilwlqm@gmail.com>
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On 2023/7/9 06:02, Daniel Xu wrote:
> Hi Leon,
> 
> On Sat, Jul 08, 2023 at 12:07:48PM +0800, Leon Hwang wrote:
>> This series introduces bpf user log to transfer error message from
>> kernel space to user space when users provide buffer to receive the
>> error message.
>>
>> Especially, when to attach XDP to device, it can transfer the error
>> message along with errno from dev_xdp_attach() to user space, if error
>> happens in dev_xdp_attach().
> 
> Have you considered adding a tracepoint instead? With some TP_printk()
> stuff I think you can achieve a similar result without having to do
> go through changing uapi.

If just for dev_xdp_attach(), I think netlink approach is better than
tracepoint approach.

As for BPF syscall, error message along with errno through uapi is a
good UX, like "create link: invalid argument (Invalid XDP flags for BPF
link attachment)" when failed to attach XDP to a device. Hence, users
are able to know the error details instead of -EINVAL or "invalid
argument" only.

Furthermore, as for other BPF syscall subcommands, we are able to
provide error message along with errno by bpf_ulog_once(&attr->xxx.ulog,
"An error").