Re: [dpdk-dev] [PATCH 1/2] virtio: initialize iopl when device is initialized

[Stephen Hemminger <stephen@networkplumber.org>]

On Fri, 6 Mar 2015 03:41:25 +0000
"Ouyang, Changchun" <changchun.ouyang@intel.com> wrote:

> 
> 
> > -----Original Message-----
> > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Stephen
> > Hemminger
> > Sent: Friday, March 6, 2015 8:45 AM
> > To: dev@dpdk.org
> > Subject: [dpdk-dev] [PATCH 1/2] virtio: initialize iopl when device is initialized
> > 
> > The virtio driver needs to use in/out instructions therefore it must initialize
> > using iopl(2) system call. The problem is that virtio initialization happens very
> > early, and any application that uses daemon() or calls eal_init later in another
> > context will fail.
> > 
> > The fix is to move the iopl into rte_eal_init.
> > 
> 
> Why need move virtio specific code into rte_eal_init?
> thanks
> Changchun
> 

The issue is that virtio has no place it can do iopl() and have the IRQ thread
work. It only shows up on real code where application is daemon, not in a toy
demo or test application.

Right now:
    gcc start
       rte_virtio_pmd_init
          iopl
    main
        daemon
            fork
                fork 
                  Process is now child of init not original process

                  rte_eal_init
                     fork (pthread) for irq thread
                                                       irq thread
                                                        (no iopl permssion)
                  program start
                  rte_pmd_virtio_configure


So the only place where iopl() can be done in the proper context
so that the IRQ (and other helper threads in future) have the correct
permissions is in eal_init.