On 8/12/2021 11:26 PM, Bjorn Helgaas wrote:
On Thu, Aug 12, 2021 at 04:51:26PM -0300, Jason Gunthorpe wrote:
On Thu, Aug 12, 2021 at 10:57:07AM -0500, Bjorn Helgaas wrote:
On Thu, Aug 12, 2021 at 10:27:28AM -0300, Jason Gunthorpe wrote:
On Wed, Aug 11, 2021 at 02:07:37PM -0500, Bjorn Helgaas wrote:
On Thu, Aug 05, 2021 at 09:23:57PM -0300, Jason Gunthorpe wrote:
Do the other bus types have a flag analogous to
PCI_ID_F_VFIO_DRIVER_OVERRIDE? If we're doing something similar to
other bus types, it'd be nice if the approach were similar.
They could, this series doesn't attempt it. I expect the approach to
be similar as driver_override was copied from PCI to other
busses. When this is completed I hope to take a look at it.
I think this would make more sense as two patches:
- Add a "PCI_ID_DRIVER_OVERRIDE" flag. This is not VFIO-specific,
since nothing in PCI depends on the VFIO-ness of drivers that use
the flag. The only point here is that driver id_table entries
with this flag only match when driver_override matches the driver.
This would require using two flags, one to indicate the above to the
PCI code and another to indicate the vfio_pci string to
file2alias. This doesn't seem justified at this point, IMHO.
I don't think it requires two flags. do_pci_entry() has:
if (flags & PCI_ID_F_VFIO_DRIVER_OVERRIDE)
strcpy(alias, "vfio_pci:");
I'm just proposing a rename:
s/PCI_ID_F_VFIO_DRIVER_OVERRIDE/PCI_ID_DRIVER_OVERRIDE/
- Update file2alias.c to export the flags and the "vfio_pci:" alias.
This seems to be the only place where VFIO comes into play, and
putting it in a separate patch will make it much smaller and it
will be clear how it could be extended for other buses.
Well, I don't want to see a flag called PCI_ID_DRIVER_OVERRIDE mapped
to the string "vfio_pci", that is just really confusing.
Hahaha, I see, that's fair :) It confused me for a long time why you
wanted "VFIO" in the flag name because from the kernel's point of
view, the flag is not related to any VFIO-ness. It's only related to
a special variety of driver_override, and VFIO happens to be one user
of it.
In my original patch I used
#define PCI_ID_DRIVER_OVERRIDE PCI_ID_F_VFIO_DRIVER_OVERRIDE
and in the pci core code I used PCI_ID_DRIVER_OVERRIDE in the "if" clause.
So we can maybe do that and leave the option to future update of the
define without changing the core code.
In the future we can have something like:
#define PCI_ID_DRIVER_OVERRIDE (PCI_ID_F_VFIO_DRIVER_OVERRIDE |
PCI_ID_F_MY_BUS_DRIVER_OVERRIDE)
The file2alias.c still have to use the exact
PCI_ID_F_VFIO_DRIVER_OVERRIDE flag to add "vfio_" prefix.
Is that better ?
I think a separate patch that maps the flag to "vfio_pci" would be
less confusing because without the distractions of the PCI core
changes, it will be obvious that "vfio_" is a file2alias thing that's
there for userspace convenience, not for kernel reasons.
Do you envision any other prefixes in the future? I hope we don't
have to clutter pci_match_device() with checking multiple flags.
Maybe the problem is that the modules.alias entry includes "vfio_" --
maybe we need a more generic prefix with just the idea of an
"alternate" driver.
Bjorn
