Re: [Xen-devel] remove the ->mapping_error method from dma_map_ops V2

[Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>]

On Tue, Nov 27, 2018 at 11:41 PM Christoph Hellwig <hch@xxxxxx> wrote:
>
> On Fri, Nov 23, 2018 at 07:55:11AM +0100, Christoph Hellwig wrote:
> > Well, I can tweak the last patch to return -EINVAL from dma_mapping_error
> > instead of the old 1 is as bool true.  The callers should all be fine,
> > although I'd have to audit them.  Still wouldn't help with being able to
> > return different errors.
>
> Any opinions?  I'd really like to make some forward progress on this
> series.

So I do think that yes, dma_mapping_error() should return an error
code, not 0/1.

But I was really hoping that the individual drivers themselves could
return error codes. Right now the patch-series has code like this:

      ret = needs_bounce(dev, dma_addr, size);
      if (ret < 0)
-         return ARM_MAPPING_ERROR;
+         return DMA_MAPPING_ERROR;

which while it all makes sense in the context of this patch-series, I
*really* think it would have been so much nicer to return the error
code 'ret' instead (which in this case is -E2BIG).

I don't think this is a huge deal, but ERR_PTR() has been hugely
successful elsewhere. And I'm not hugely convinced about all these
"any address can be valid" arguments. How the hell do you generate a
random dma address in the last page that isn't even page-aligned?

                     Linus

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