Re: [dpdk-dev] [PATCH] bus/pci: fix vfio mode

[Thomas Monjalon <thomas@monjalon.net>]

30/10/2017 10:27, Thomas Monjalon:
> 30/10/2017 10:17, Gaëtan Rivet:
> > Hi Ferruh,
> > 
> > On Mon, Oct 30, 2017 at 02:00:43AM -0700, Ferruh Yigit wrote:
> > > On 10/30/2017 1:06 AM, Gaëtan Rivet wrote:
> > > > Hi Jerin,
> > > > 
> > > > On Sat, Oct 28, 2017 at 11:50:52AM +0530, Jerin Jacob wrote:
> > > >> The definition of VFIO_PRESENT is "eal_vfio.h", Fail to
> > > >> include eal_vfio.h will result in disabling vfio.
> > > >>
> > > >> Fixes: 279b581c897d ("vfio: expose functions")
> > > >>
> > > > 
> > > > Thanks for the fix, sorry for VFIO.
> > > > I tried to let go of VFIO_PRESENT in the PCI patchset, unfortunately I did
> > > > not do a good-enough job.
> > > > 
> > > > Instead of reinstating the dependency on the private eal_vfio.h header,
> > > > I'd suggest replacing all VFIO_PRESENT references within the PCI bus by
> > > > RTE_EAL_VFIO, and make the pci_vfio.c compilation depend on it within
> > > > the linux Makefile. Something like:
> > > > 
> > > > ---8<---
> > > > 
> > > > grep -rl VFIO_PRESENT drivers/bus/pci/linux/ |while read -r file
> > > > do sed -i 's;VFIO_PRESENT;RTE_EAL_VFIO;' $file
> > > > done
> > > 
> > > VFIO_PRESENT is the combination of the if user enabled VFIO and if Linux kernel
> > > supports it.
> > > 
> > > Why not add same check and VFIO_PRESENT definition to rte_vfio.h:
> > > 
> > >   --- a/lib/librte_eal/common/include/rte_vfio.h
> > >   +++ b/lib/librte_eal/common/include/rte_vfio.h
> > >   @@ -34,7 +34,13 @@
> > >    #ifndef _RTE_VFIO_H_
> > >    #define _RTE_VFIO_H_
> > > 
> > >   +#if !defined(VFIO_PRESENT) && defined(RTE_EAL_VFIO)
> > >   +#include <linux/version.h>
> > >   +#if LINUX_VERSION_CODE >= KERNEL_VERSION(3, 6, 0)
> > >    #include <linux/vfio.h>
> > >   +#define VFIO_PRESENT
> > >   +#endif /* >= 3.6.0 */
> > >   +#endif
> > >   +
> > >   +#ifdef VFIO_PRESENT
> > > 
> > >   ... Need to wrap here in case VFIO disabled ...
> > > 
> > >   #endif
> > > 
> > 
> > It would work indeed.
> > 
> > I mostly dislike having whole compilation units disabled silently on a
> > linux version check. I think that if someone wanted to support kernels <
> > 3.6, they ought to do the work of disabling RTE_EAL_VFIO.
> > 
> > A build error could be thrown to help those users toward the right
> > solution, but I think that the meaning of having this option enabled
> > should be enforced: if it is enabled, it is compiled. If dependencies
> > are not met, then the option should be disabled.
> 
> +1 to avoid implicit disabling.

To make it clear, we can disable VFIO automatically if not supported by
the kernel at compilation time, but there should be a warning.