[dpdk-dev] [PATCH v10 13/14] eal/pci: Add rte_eal_dev_attach/detach() functions

[Maxime Leroy]

Hi Tetsuya,

On Sat, Feb 21, 2015 at 4:49 AM, Tetsuya Mukawa <mukawa at igel.co.jp> wrote:
> On 2015/02/21 0:20, Maxime Leroy wrote:
[...]
>> Why you want to add devargs in the devargs_list, if there are no needs
>> to store this information ?
>
> In eal initialization code, virtual device names stored in devargs are
> checked not to register a same device name twice.
> And each init function of PMD just trust a device name received by eal.
> So there is no code in PMD to check whether device name is unique.
>

I disagree with you. This check is not present in the master branch.

You have added this check in your hotplug patchset, in this patch:
[PATCH v10 10/14] eal/pci: Add a function to remove the entry of
devargs list
See: http://dpdk.org/ml/archives/dev/2015-February/013712.html

Thus the problem should be already exist without your patches in the
master branch.

For example according to you, this testpmd command should create 2
devices with the same name:
testpmd -c 0xc --vdev eth_pcap0,iface=eth0 --vdev eth_pcap0,iface=eth1
-n 2 -- -i

But it's not the case:
PMD: Initializing pmd_pcap for eth_pcap0
PMD: Creating pcap-backed ethdev on numa socket 0
PMD: Initializing pmd_pcap for eth_pcap0
PMD: Creating pcap-backed ethdev on numa socket 0
PMD: rte_eth_dev_allocate: Ethernet Device with name eth_pcap0 already
allocated!

In fact, it's not possible for any PMD_VDEV in the dpdk repo to create
2 devices with the same name.
All the virtual device initialization functions use the
rte_eth_dev_allocate function. This function prevents to create two
ethernet devices with the same name:

     if (rte_eth_dev_allocated(name) != NULL) {
        PMD_DEBUG_TRACE("Ethernet Device with name %s already
allocated!\n", name);
        return NULL;
    }


> For example, according to your suggestion, how to prevent below case?
> $ ./testpmd -c f -n 1 -- -i
> testpmd> port attach eth_pcap0,iface=eth0
> testpmd> port attach eth_pcap0,iface=eth1
>
> Also, type below, after doing above.
> testpmd> port detach 0
>
> Probably port 0 will be "eth_pcap0,iface=eth0".
> But uninit code of PMD only receives a device name like 'eth_pcap0'.
> (We have 2 'eth_pcap0' devices in PMD.)
>
> To prevent above case, probably we have 2 options at least.
> One is changing init code of all virtual PMDs not to register same
> device name.

There are no need to change init code of all virtual PMDs to not
register the same device name 2 times.
Because it's already not possible to create 2 virtual device with the
same name. (see my point above)

> The other is to use devargs_list in EAL, and call init code of PMD with
> a unique device name.

Thus there are no needs to use the devargs_list for that.

>
[..]
>>
>> But you don't call rte_eal_devargs_add with RTE_DEVTYPE_WHILISTED_PCI
>> in  rte_eal_dev_attach_pdev ?
>
> Yes, I don't.
> Hotplug functions should not change BLACKLIST and WHITELIST.
> So not to touch the list is correct behavior.

Yes the correct behaviour for Hotplug functions is to not use the
devargs_list for physical and virtual devices !

Regards,

Maxime