Re: rte_eth_dev_attach returns 0, although device is not attached

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 8/4/2016 3:54 PM, Igor Ryzhov wrote:
> 
>> 4 авг. 2016 г., в 16:21, Ferruh Yigit <ferruh.yigit@intel.com
>> <mailto:ferruh.yigit@intel.com>> написал(а):
>>
>> On 8/4/2016 12:51 PM, Igor Ryzhov wrote:
>>> Hello Ferruh,
>>>
>>>> 4 авг. 2016 г., в 14:33, Ferruh Yigit <ferruh.yigit@intel.com
>>>> <mailto:ferruh.yigit@intel.com>> написал(а):
>>>>
>>>> Hi Igor,
>>>>
>>>> On 8/3/2016 5:58 PM, Igor Ryzhov wrote:
>>>>> Hello.
>>>>>
>>>>> Function rte_eth_dev_attach can return false positive result.
>>>>> It happens because rte_eal_pci_probe_one returns zero if no driver
>>>>> is found for the device:
>>>>> ret = pci_probe_all_drivers(dev);
>>>>> if (ret < 0)
>>>>> goto err_return;
>>>>> return 0;
>>>>> (pci_probe_all_drivers returns 1 in that case)
>>>>>
>>>>> For example, it can be easily reproduced by trying to attach virtio
>>>>> device, managed by kernel driver.
>>>>
>>>> You are right, and I did able to reproduce this issue with virtio as you
>>>> suggest.
>>>>
>>>> But I wonder why rte_eth_dev_get_port_by_addr() is not catching this.
>>>> Perhaps a dev->attached check needs to be added into this function.
>>
>> With a second check, rte_eth_dev_get_port_by_addr() catches it if the
>> driver is missing.
>>
>> But for virtio case, problem is not missing driver.
>> Problem is eth_virtio_dev_init() is returning a positive value on fail.
>>
>> Call stack is:
>> rte_eal_pci_probe_one
>>    pci_probe_all_drivers
>>        rte_eal_pci_probe_one_driver
>>            rte_eth_dev_init
>>               eth_virtio_dev_init
>>
>> So rte_eal_pci_probe_one_driver() also returns positive value, as no
>> driver found, and rte_eth_dev_get_port_by_addr() returns a valid
>> port_id, since rte_eth_dev_init() allocated an eth_dev.
>>
>> Briefly, this can be fixed in virtio pmd, instead of eal pci.
>>
>>>>
>>>>>
>>>>> I think it should be:
>>>>> ret = pci_probe_all_drivers(dev);
>>>>> if (ret)
>>>>> goto err_return;
>>>>> return 0;
>>>>
>>>> Your proposal looks good to me. Will you send a patch?
>>>
>>
>> Original code silently ignores the if driver is missing for that dev,
>> although it is still questionable, I think we can keep this as it is.
>>
>>> Patch sent.
>>
>> Sorry for this, but can you please test with following modification in
>> virtio:
>> index 07d6449..c74eeee 100644
>> --- a/drivers/net/virtio/virtio_ethdev.c
>> +++ b/drivers/net/virtio/virtio_ethdev.c
>> @@ -1156,7 +1156,7 @@ eth_virtio_dev_init(struct rte_eth_dev *eth_dev)
>>        if (pci_dev) {
>>                ret = vtpci_init(pci_dev, hw, &dev_flags);
>>                if (ret)
>> -                       return ret;
>> +                       return -1;
>>        }
>>
>>        /* Reset the device although not necessary at startup */
> 
> I think it's not a good change, because it will break the idea of this
> patch - http://dpdk.org/browse/dpdk/commit/?id=ac5e1d83

Yes, breaks this one, I wasn't aware of this patch. But in this patch,
commit log says: "return 1 to tell the upper layer we
don't take over this device.", I am not sure upper layer designed for this.

> 
> Also, with your patch the application will not start, because
> rte_eal_pci_probe will fail:
> 
> if (ret < 0)
> rte_exit(EXIT_FAILURE, "Requested device " PCI_PRI_FMT
>  " cannot be used\n", dev->addr.domain, dev->addr.bus,
>  dev->addr.devid, dev->addr.function);

Yes it fails, and this looks like intended behavior. This failure is
correct according code.

> 
> And now I think that maybe we should change the way rte_eal_pci_probe works.
> I think we shouldn't stop the application if just one of PCI devices is
> not probed successfully.

Agreed. Overall rte_exit() usage already discussed a few times.

I think best option is:
- don't exit app if rte_eal_pci_probe() fails, only print an error.
- eth_virtio_dev_init() return negative error value for all error cases
(including device managed by kernel)

Or perhaps RTE_KDRV_UNKNOWN check can be moved from virtio_pmd into
higher level and can be done for all devices. Like
pci_probe_one_driver() can fail if device driver is RTE_KDRV_UNKNOWN.

Any comments?


> 
>>
>>
>>>
>>>>
>>>>> Best regards,
>>>>> Igor
>