linux-kernel - Re: [PATCH net-next 07/11] net: hns3: adds debug messages to identify eth down cause

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Message-ID: <9ae85be2-b958-ecb4-2980-ca7e977606a1@huawei.com>
Date:   Fri, 26 Jul 2019 10:21:27 +0800
From:   liuyonglong <liuyonglong@...wei.com>
To:     Saeed Mahameed <saeedm@...lanox.com>,
        "tanhuazhong@...wei.com" <tanhuazhong@...wei.com>,
        "davem@...emloft.net" <davem@...emloft.net>
CC:     "lipeng321@...wei.com" <lipeng321@...wei.com>,
        "yisen.zhuang@...wei.com" <yisen.zhuang@...wei.com>,
        "salil.mehta@...wei.com" <salil.mehta@...wei.com>,
        "linuxarm@...wei.com" <linuxarm@...wei.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 07/11] net: hns3: adds debug messages to identify
 eth down cause

We will change all of them to netif_msg_drv() which is default off
Thanks for your reply!

On 2019/7/26 5:59, Saeed Mahameed wrote:
> On Thu, 2019-07-25 at 20:28 +0800, liuyonglong wrote:
>>
>> On 2019/7/25 3:12, Saeed Mahameed wrote:
>>> On Wed, 2019-07-24 at 11:18 +0800, Huazhong Tan wrote:
>>>> From: Yonglong Liu <liuyonglong@...wei.com>
>>>>
>>>> Some times just see the eth interface have been down/up via
>>>> dmesg, but can not know why the eth down. So adds some debug
>>>> messages to identify the cause for this.
>>>>
>>>
>>> I really don't like this. your default msg lvl has NETIF_MSG_IFDOWN
>>> turned on .. dumping every single operation that happens on your
>>> device
>>> by default to kernel log is too much ! 
>>>
>>> We should really consider using trace buffers with well defined
>>> structures for vendor specific events. so we can use bpf filters
>>> and
>>> state of the art tools for netdev debugging.
>>>
>>
>> We do this because we can just see a link down message in dmesg, and
>> had
>> take a long time to found the cause of link down, just because
>> another
>> user changed the settings.
>>
>> We can change the net_open/net_stop/dcbnl_ops to msg_drv (not default
>> turned on),  and want to keep the others default print to kernel log,
>> is it acceptable?
>>
> 
> acceptable as long as debug information are kept off by default and
> your driver doens't spam the kernel log.
> 
> you should use dynamic debug [1] and/or "off by default" msg lvls for
> debugging information..
> 
> I couldn't find any rules regarding what to put in kernel log, Maybe
> someone can share ?. but i vaguely remember that the recommendation
> for device drivers is to put nothing, only error/warning messages.
> 
> [1] 
> https://www.kernel.org/doc/html/v4.15/admin-guide/dynamic-debug-howto.html
> 
>>>> @@ -1593,6 +1603,11 @@ static int hns3_ndo_set_vf_vlan(struct
>>>> net_device *netdev, int vf, u16 vlan,
>>>>  	struct hnae3_handle *h = hns3_get_handle(netdev);
>>>>  	int ret = -EIO;
>>>>  
>>>> +	if (netif_msg_ifdown(h))
>>>
>>> why msg_ifdown ? looks like netif_msg_drv is more appropriate, for
>>> many
>>> of the cases in this patch.
>>>
>>
>> This operation may cause link down, so we use msg_ifdown.
>>
> 
> ifdown isn't link down.. 
> 
> to be honest, I couldn't find any documentation explaining how/when to
> use msg lvls, (i didn't look too deep though), by looking at other
> drivers, my interpretations is:
> 
> ifdup (open/boot up flow)
> ifdwon (close/teardown flow)
> drv (driver based or dynamic flows) 
> etc .. 
> 
> -Saeed.
>