Re: [Qemu-devel] [PATCH] macio ide: Do remainder access asynchronously

[Mark Cave-Ayland]

On 26/05/14 09:32, Alexander Graf wrote:

> The macio IDE controller has some pretty nasty magic in its implementation to
> allow for unaligned sector accesses. We used to handle these accesses
> synchronously inside the IO callback handler.
>
> However, the block infrastructure changed below our feet and now it's impossible
> to call a synchronous block read/write from the aio callback handler of a
> previous block access.
>
> Work around that limitation by making the unaligned handling bits also go
> through our asynchronous handler.
>
> This fixes booting Mac OS X for me.

Hmmm nasty. I've never had a problem booting my two Darwin test images, 
but I've quickly tried the patch on my complete set of test suite 
booting up to the installer and haven't seen any regressions yet.

Incidentally, whilst investigating Zoltan's bug with the ATAPI DMA I 
looked into where we were with byte-aligned DMA, and with Kevin's 
patches applied it's fairly close.

The underlying bdrv_*() functions now use the unaligned-aware functions, 
and the DMA API takes a QEMUSGList as input which is good. However, 
moving down between the layers we switch back to a BlockDriverState 
before calling the unaligned functions so we lose the SGList and switch 
to lba/count again.

It looks like most of it is there, it just needs a few tweaks to get the 
SGList all the way down the unaligned functions. And I will definitely 
be happy on the day we get to rip out all of the unaligned code from 
macio :)


ATB,

Mark.