netdev - Re: [PATCH net-next 2/5] ibmvnic: Include documentation for ibmvnic sysfs files

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Date:   Mon, 31 Aug 2020 14:51:49 -0500
From:   Thomas Falcon <tlfalcon@...ux.ibm.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, drt@...ux.vnet.ibm.com,
        sukadev@...ux.vnet.ibm.com, ljp@...ux.vnet.ibm.com,
        cforno12@...ux.ibm.com
Subject: Re: [PATCH net-next 2/5] ibmvnic: Include documentation for ibmvnic
 sysfs files


On 8/31/20 2:07 PM, Jakub Kicinski wrote:
> On Mon, 31 Aug 2020 11:58:10 -0500 Thomas Falcon wrote:
>> Include documentation for existing ibmvnic sysfs files,
>> currently only for "failover," which is used to swap
>> the active hardware port to a backup port in redundant
>> backing hardware or failover configurations.
>>
>> Signed-off-by: Thomas Falcon <tlfalcon@...ux.ibm.com>
>> ---
>>   Documentation/ABI/testing/sysfs-driver-ibmvnic | 14 ++++++++++++++
>>   1 file changed, 14 insertions(+)
>>   create mode 100644 Documentation/ABI/testing/sysfs-driver-ibmvnic
>>
>> diff --git a/Documentation/ABI/testing/sysfs-driver-ibmvnic b/Documentation/ABI/testing/sysfs-driver-ibmvnic
>> new file mode 100644
>> index 0000000..7fa2920
>> --- /dev/null
>> +++ b/Documentation/ABI/testing/sysfs-driver-ibmvnic
>> @@ -0,0 +1,14 @@
>> +What:		/sys/devices/vio/<our device>/failover
>> +Date:		June 2017
>> +KernelVersion:	4.13
>> +Contact:	linuxppc-dev@...ts.ozlabs.org
>> +Description:	If the ibmvnic device has been configured with redundant
>> +		physical NIC ports, the user may write "1" to the failover
>> +		file to trigger a device failover, which will reset the
>> +		ibmvnic device and swap to a backup physical port. If no
>> +		redundant physical port has been configured for the device,
>> +		the device will not reset and -EINVAL is returned. If anything
>> +		other than "1" is written to the file, -EINVAL will also be
>> +		returned.
>> +Users:		Any users of the ibmvnic driver which use redundant hardware
>> +		configurations.
> Could you elaborate what the failover thing is? Is it what net_failover
> does or something opposite? (you say "backup physical port" which
> sounds like physical port is a backup.. perhaps some IBM nomenclature
> there worth clarifying?)

Hi Jakub,

When creating a SRIOV VNIC device on a Power system, the user will 
specify one or more ports to use from physical NIC's available to the 
Power Hypervisor. These aren't visible to the Linux OS. In a failover 
configuration, the VNIC will have one active port and at least one other 
port in backup or standby mode. It's similar to the bonding driver's 
active-backup mode. If the hypervisor detects a problem with the active 
port, it will swap in the backup port and send a signal to the VNIC 
driver that it should reset, which is needed to activate the new port. 
There is also a mechanism through which the driver can force this 
operation in case the hypervisor does not detect an issue with the 
active port. This mechanism can be triggered by an administrator or with 
userspace tools through the 'failover' device file in sysfs.

Tom