netdev - Re: [PATCH v9 net-next 13/14] pds_core: publish events to the clients

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Date:   Thu, 13 Apr 2023 16:42:08 -0700
From:   Shannon Nelson <shannon.nelson@....com>
To:     Jakub Kicinski <kuba@...nel.org>, Leon Romanovsky <leon@...nel.org>
Cc:     brett.creeley@....com, davem@...emloft.net, netdev@...r.kernel.org,
        drivers@...sando.io, jiri@...nulli.us
Subject: Re: [PATCH v9 net-next 13/14] pds_core: publish events to the clients

On 4/13/23 10:10 AM, Jakub Kicinski wrote:
> 
> On Thu, 13 Apr 2023 20:07:04 +0300 Leon Romanovsky wrote:
>>> Hm, my memory may be incorrect and I didn't look at the code but
>>> I thought that knob came from the "hit-less upgrade" effort.
>>> And for "hit-less upgrade" not respawning the devices was the whole
>>> point.
>>>
>>> Which is not to disagree with you. What I'm trying to get at is that
>>> there are different types of reset which deserve different treatment.
>>
>> I don't disagree with you either, just have a feeling that proposed
>> behaviour is wrong.
> 
> Shannon, can you elaborate on what the impact of the reset is?
> What loss of state and/or configuration is possible?

The device has a couple different cases that might generate the RESET 
message:
  - crashed and recovered, no state saved
  - FW restarted, some or all state saved
There are some variations on this, but these are the two general cases.

We can see in the existing ionic driver there already is some handling 
of this where the driver sees the FW come back and is able to replay the 
Rx filters and Rx mode configurations.  If and when we are able to add 
an Eth client through pds_core it will want this message so that it can 
replay configuration in the same way.  This case will also want the Link 
Down event so that it can do the right thing with the netdev.

For the VFio/Migration support (pds_vfio) the RESET message is 
essentially a no-op if nothing is happening.  But if the system is in 
the middle of a migration it offers the ability to "cleanly" fail the 
migration and let the system get ready to try again.

For the vDPA case (pds_vdpa) we can trigger the config_cb callback to 
get the attention of the stack above us to suggest it look at current 
status and respond as needed, whether that is a Link Change or a Reset.

sln