On Thu, Aug 11, 2011 at 1:10 PM, Paolo Bonzini <pbonz...@redhat.com> wrote: > On 08/11/2011 09:58 AM, Stefan Hajnoczi wrote: >> >> On Thu, Aug 04, 2011 at 07:14:43PM +0200, Paolo Bonzini wrote: >>> >>> These helpers do a full transfer from an in-memory buffer to >>> target memory, with full support for MMIO areas. It will be used to >>> store >>> the reply of an emulated command into a QEMUSGList provided by the >>> adapter. >>> >>> Signed-off-by: Paolo Bonzini<pbonz...@redhat.com> >>> --- >>> cutils.c | 8 +++--- >>> dma-helpers.c | 63 >>> +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ >>> dma.h | 5 ++++ >>> 3 files changed, 72 insertions(+), 4 deletions(-) >> >> I don't understand this patch. If we have a memory buffer that needs to >> be transferred to target memory, then there is no need for bounce >> buffers or cpu_physical_memory_map(). >> >> Can we use cpu_physical_memory_rw() on each sglist element instead? No >> -EAGAIN necessary because the memory buffer already acts as the local >> bounce buffer. > > Doh, you're obviously right. I don't know what I was thinking. :) > > What do you think about passing the residual bytes for short transfers? > Should I look into updating BlockDriverCompletionFunc, or is the approach > of patch 2 okay? If I have an excuse to learn more about Coccinelle, that > can be fun. :)
The bdrv_aio_readv() and bdrv_aio_writev() functions don't have the concept of residual bytes. They only work on fully completed I/O operations. If there is an error they pass -errno. Therefore I don't think BlockDriverCompletionFunc is the right type to add residual bytes to. It seems that residual bytes are a SCSI layer concept that the block layer does not deal with. Stefan
