Re: [dpdk-dev] [PATCH v10 05/11] net/failsafe: add flexible device definition

["Gaëtan Rivet" <gaetan.rivet@6wind.com>]

Hi Ferruh,

(Thanks for the review by the way, I will answer the other more lengthy
emails in due time)

On Mon, Jul 17, 2017 at 04:45:59PM +0100, Ferruh Yigit wrote:
> On 7/15/2017 6:57 PM, Gaetan Rivet wrote:
> > Add the "exec" device type.
> > The parameters given to this type of device will be executed in a shell.
> > The output of this command is then used as a definition for a device.
> > 
> > That command can be re-interpreted if the related device is not
> > plugged-in. It allows for a device definition to react to system
> > changes (e.g. changing PCI bus for a given device).
> > 
> > Signed-off-by: Gaetan Rivet <gaetan.rivet@6wind.com>
> > Acked-by: Olga Shern <olgas@mellanox.com>
> > ---
> >  doc/guides/nics/fail_safe.rst           | 20 +++++++
> >  drivers/net/failsafe/failsafe_args.c    | 95 +++++++++++++++++++++++++++++++++
> >  drivers/net/failsafe/failsafe_ether.c   |  7 +++
> >  drivers/net/failsafe/failsafe_private.h |  4 ++
> >  4 files changed, 126 insertions(+)
> > 
> > diff --git a/doc/guides/nics/fail_safe.rst b/doc/guides/nics/fail_safe.rst
> > index 5ec3031..be73d7e 100644
> > --- a/doc/guides/nics/fail_safe.rst
> > +++ b/doc/guides/nics/fail_safe.rst
> > @@ -87,6 +87,19 @@ Fail-safe command line parameters
> >    additional sub-device parameters if need be. They will be passed on to the
> >    sub-device.
> >  
> > +- **exec(<shell command>)** parameter
> > +
> > +  This parameter allows the user to provide a command to the fail-safe PMD to
> > +  execute and define a sub-device.
> > +  It is done within a regular shell context.
> > +  The first line of its output is read by the fail-safe PMD and otherwise
> > +  interpreted as if passed by the regular **dev** parameter.
> > +  Any other line is discarded.
> > +  If the command fail or output an incorrect string, the sub-device is not
> > +  initialized.
> > +  All commas within the ``shell command`` are replaced by spaces before
> > +  executing the command. This helps using scripts to specify devices.
> > +
> >  - **mac** parameter [MAC address]
> >  
> >    This parameter allows the user to set a default MAC address to the fail-safe
> > @@ -135,6 +148,13 @@ This section shows some example of using **testpmd** with a fail-safe PMD.
> >           -w 'net_failsafe0,mac=de:ad:be:ef:01:02,dev(84:00.0),dev(net_ring0)'
> >           -w 81:00.0 -- -i
> >  
> > +#. Start testpmd using a flexible device definition
> > +
> > +   .. code-block:: console
> > +
> > +      $RTE_TARGET/build/app/testpmd -c 0xff -n 4 --no-pci \
> > +         --vdev='net_failsafe0,exec(echo 84:00.0)' -- -i
> 
> Hi Gaetan,
> 
> What is the usecase for this feature.
> 
> How this is different from --vdev='net_failsafe0,dev(`echo 84:00.0`)' ?

This version would be interpreted once, at the launch of the fail-safe
PMD.

The exec option will execute the command again each time the fail-safe
tries to probe the sub_device. This means that in a live VM migration
context, the sub_device can change PCI address (for example), and still be
matched by the command using other identifying info (MAC address,
class_id, ...).

It must be reinterpreted upon plugin of the sub_device,
as the output would change from the time the fail-safe was started.

-- 
Gaëtan Rivet
6WIND