Re: [dpdk-dev] [PATCH 1/2] bus/pci: Fail rte_pci_probe if probing all whitelisted devices fail.

[Stephen Hemminger <stephen@networkplumber.org>]

On Wed, 28 Aug 2019 01:00:16 +0530
Nitin Katiyar <nitin.katiyar@ericsson.com> wrote:

> Even if whitelist of devices is provided, rte_pci_probe() increments
> the probed counter for all the devices present in the system. If probe
> fails for all the whitelisted devices it still return success because
> failed and probed counts don't match.
> 
> This patch increments probed count only when devices are actually
> probed.
> 
> Signed-off-by: Nitin Katiyar <nitin.katiyar@ericsson.com>
> Signed-off-by: Venkatesan Pradeep <venkatesan.pradeep@ericsson.com>

There are two differing interpretations of this.
The simple case which is what your patch fixes is where user gives bad
arguments and no devices are present.

But the more complex case is where the devices show up later via hotplug
or other discovery mechanism. For example, on Hyper-V/Azure SRIOV PCI devices
can show up after application is started.  Your patch might break the
use case of where an application is started before the VF is available.

More detailed example:

1. VM is started.
2. VF is take offline for maintenance or migration.
3. DPDK application is started with whitelist option (no usable PCI found).
4. VF becomes available after maintenance.

Yes, this a somewhat made up order which is unlikely to happen in
real life. But there is nothing stopping it from happening.

I often recommend to customers using whitelist because the typical appliance
scenario has a management interface, and you don't want the DPDK interacting
with the VF of the management interface.

Therefore, from my point of view, this patch is a NO.