Re: [Qemu-devel] [PATCH 1/1] ide: unify io_buffer_offset increments

[Paolo Bonzini <pbonzini@redhat.com>]

On 26/08/2015 01:45, John Snow wrote:
> IDEState's io_buffer_offset was originally added to keep track of offsets
> in AHCI rather exclusively, but it was added to IDEState instead of an
> AHCI-specific structure.

Interesting to see something weird turn into feature. :)

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

> AHCI fakes all PIO transfers using DMA and a scatter-gather list. When
> the core or atapi layers invoke HBA-specific mechanisms for transfers,
> they do not always know that it is being backed by DMA or a sglist, so
> this offset is not always updated by the HBA code everywhere.
> 
> If we modify it in dma_buf_commit, however, any HBA that needs to use
> this offset to manage operating on only part of a sglist will have
> access to it.
> 
> This will fix ATAPI PIO transfers performed through the AHCI HBA,
> which were previously not modifying this value appropriately.
> 
> This will fix ATAPI PIO transfers larger than one sector.