RE: [patch V2 07/33] genirq/msi: Provide msi_create/free_device_irq_domain()

[Tian, Kevin]

> From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Sent: Thursday, November 24, 2022 4:36 PM
> 
> On Thu, Nov 24 2022 at 01:07, Kevin Tian wrote:
> >> From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > I looked at it from the outmost invocation:
> >
> > @@ -436,6 +436,9 @@ int __pci_enable_msi_range(struct pci_de
> >  	if (rc)
> >  		return rc;
> >
> > +	if (!pci_setup_msi_device_domain(dev))
> > +		return -ENODEV;
> > +
> >
> > the current style kind of converts meaningful -EINVAL/-ENOMEM/etc.
> > into -ENODEV.
> 
> But go to the call sites of the various places in drivers which set up
> MSI or MSI-X and check whether anything evaluates those error codes in a
> meaningful way.
> 
> Some of them print the error code, but that does not help much because
> the error code does not allow you to pin point the place which returns
> that. If you just analyze the pci_alloc_irq_vectors_affinity() call then
> you find at least 10 places, which can return -ENOMEM. So how is that
> meaningful and helpful?
> 
> All it tells you is that some memory allocation failed. In that case the
> failure of the PCI/MSI[-X] setup is the least of the problems.
> 
> Where error codes are mandatory are user space interfaces, but in the
> kernel a simple fail/success like we have with many interfaces which
> just return a NULL pointer on fail is sufficient.
> 
> Just because the kernel historically propagated error codes all over the
> place does not make them useful or meaningful.
> 

Good learning. Thanks.