Re: [PATCH] pci_dma_rw: return correct value instead of 0

[Stefano Garzarella <sgarzare@redhat.com>]

On Thu, Jul 30, 2020 at 09:58:21AM +0100, Peter Maydell wrote:
> On Thu, 30 Jul 2020 at 08:42, Stefano Garzarella <sgarzare@redhat.com> wrote:
> > I agree that it is better to return the dma_memory_rw() return value, but
> > at first look, no one seems to check the return value of pci_dma_rw(),
> > pci_dma_read(), andpci_dma_write().
> >
> > Should we make them void?
> 
> In general code (eg device models) that issues memory transactions
> need to have a mechanism for finding out whether the transaction
> succeeds. Traditionally QEMU didn't have the concept of a
> transaction failing, but we have added it, starting with the
> APIs at the bottom level (the address_space_* ones). We haven't
> always plumbed the error-handling (or the memory-transaction
> input, for that matter) through to some of these other APIs.
> I think for consistency we should do that, and ideally we
> should make all these APIs look the same as the base-level
> address_space* ones, which would mean returning a MemTxError
> rather than a bool.

Yeah, that makes a lot of sense to me.

> 
> We should also figure out why the dma_* functions exist at all:
> they include some calls to dma_barrier(), but not all devices
> do DMA with the dma_* functions, so we have an inconsistency
> that should be sorted out...
> 

I've never looked in detail, but I agree we should have more consistency.

Thanks for the details!
Stefano