Re: [Xen-devel] [Question] Proper location for Linux error code (-EPROBE_DEFER) in Xen

[Oleksandr <olekstysh@xxxxxxxxx>]

On 01.08.19 18:46, Jan Beulich wrote:
> On 01.08.2019 16:54, Oleksandr wrote:
> > On 01.08.19 17:34, Jan Beulich wrote:
> > > On 01.08.2019 16:31, Oleksandr wrote:
> > > >     This is needed for the upcoming V2 of the IPMMU driver (ARM) [1] which may 
> > > > request
> > > >     deferred probing (returns -EPROBE_DEFER) depending on what device will be 
> > > > probed the first
> > > >     (Root device must be registered before Cache devices. If not the case,
> > > >     driver will deny further Cache device probes until Root device is 
> > > > registered).
> > > >
> > > > As we can't guarantee a fixed pre-defined order for the device nodes in DT, we 
> > > > need to be ready for the situation where devices being probed
> > > > in "any" order. So, framework (drivers/passthrough/arm/iommu.c) will be 
> > > > modified a bit to be able to handle -EPROBE_DEFER returning by driver.
> > > I'm sure this can be had without introducing a new error code.
> > By reusing existing one (EAGAIN comes to mind)?
> For example. Or by using some positive value instead of the (negative)
> errno.h ones.
Actually, why not? Thank you.

We could find common ground on what driver's init callback should return 
if driver wants to request deferred probing and document this behavior 
in device_init usage.
I would use EAGAIN, but I am open to other options here.

Julien, what do you think?


--
Regards,

Oleksandr Tyshchenko


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