Re: [dpdk-dev] [PATCH] app/testpmd: change port detach interface

[Nithin Dabilpuram <nithind1988@gmail.com>]

On Fri, May 17, 2019 at 10:59:38AM +0200, Thomas Monjalon wrote:
> 17/05/2019 10:55, Nithin Dabilpuram:
> > On Wed, May 15, 2019 at 09:27:22AM +0200, Thomas Monjalon wrote:
> > > 15/05/2019 08:52, Nithin Dabilpuram:
> > > > Hi Thomas,
> > > > On Tue, May 14, 2019 at 05:39:30PM +0200, Thomas Monjalon wrote:
> > > > > Hi,
> > > > > 
> > > > > 13/05/2019 13:21, Nithin Dabilpuram:
> > > > > > With the latest published interface of
> > > > > > rte_eal_hotplug_[add,remove](), and rte_eth_dev_close(),
> > > > > > rte_eth_dev_close() would cleanup all the data structures of
> > > > > > port's eth dev leaving the device common resource intact
> > > > > > if RTE_ETH_DEV_CLOSE_REMOVE is set in dev flags.
> > > > > > So "port detach" (~hotplug remove) should be able to work,
> > > > > > with device identifier like "port attach" as eth_dev could have
> > > > > > been closed already and rte_eth_devices[port_id] reused.
> > > > > 
> > > > > "port attach" uses devargs as identifier because there
> > > > > is no port id before creating it. But "detach port" uses
> > > > > logically the port id to close.
> > > > 
> > > > But if "port close" was already called on that port,
> > > > eth_dev->state would be set as RTE_ETH_DEV_UNUSED and
> > > > that port id could be reused.
> > > > So after "port close" if we call "port detach", isn't it
> > > > incorrect to use the same port id ?
> > > 
> > > Yes it is incorrect to close a port which is already closed :)
> > > 
> > > > > > This change alters "port detach" cmdline interface to
> > > > > > work with device identifier like "port attach".
> > > > > 
> > > > > The word "port" means an ethdev port, so it should be
> > > > > referenced with a port id.
> > > > > If you want to close an EAL rte_device, then you should
> > > > > rename the command.
> > > > > But testpmd purpose should be to work with ethdev ports only.
> > > > 
> > > > Renaming the command to "detach <identifier>" ?
> > > 
> > > Yes something like that.
> > > But why do you want to manage rte_device in testpmd?
> > > Being able to close ports in not enough?
> > > Please describe a scenario.
> > >
> > 
> > We just want to support testing hotplug detach along with
> > hotplug attach from testpmd. Currently there is no way to detach
> > if we close the port first.
> 
> OK
So can I send next revision with command renamed to "detach <identifier>" ?
> 
> > Another reason is that in our new PMD, for detaching one specific port,
> > we need more than one try as the PMD might return -EAGAIN.
> > So with the current "port detach" implementation, after closing the port,
> > if PMD returns -EAGAIN for rte_dev_remove() call, there is no way to
> > try it again.
> 
> This is a bug.
> Should we catch -EAGAIN somewhere?

It is already caught in local_dev_remove() and
rte_dev_remove() fails. Only problem as I said below is
in testpmd if first call to detach_port_device() i.e handler of "port detach", 
rte_dev_remove() returns -EAGAIN and PMD cleaned up the resources partially like eth_dev
resources, the second time call cannot work port_id will not be valid anymore.

> 
>