[Qemu-devel] Re: [PATCH 0/5] Direct memory access for devices (v2)

[Anthony Liguori <anthony@codemonkey.ws>]

Avi Kivity wrote:
> One of the deficiencies of the current device layer is that it can only access
> guest RAM via cpu_physical_memory_rw().  This means that the device emulation
> code must copy the memory to or from a temporary buffer, even though the host
> offers APIs which allow direct access to memory.  This reduces efficiency on
> DMA capable devices, especially disks.
>
> This patchset introduces a complement to the read/write API,
> cpu_physical_memory_map() which allows device emulation code to map
> guest memory directly.  The API bounces memory regions which cannot be
> mapped (such as mmio regions) using an internal buffer.
>
> As an example, IDE emulation is converted to use the new API.  This exposes
> another deficiency: lack of scatter/gather support in the block layer.  To
> work around this, a vectored block API is introduced, currently emulated
> by bouncing.  Additional work is needed to convert all block format drivers
> to use the vectored API.
>   

Applied all.  Thanks.

Regards,

Anthony Liguori

> Changes from v1:
>  - documented memory mapping API
>  - added access_len parameter to unmap operation, to indicate how much
>    memory was actually accessed
>  - move QEMUIOVector to cutils.c, and add flatten/unflatten operations
>  - change block format driver API to accept a QEMUIOVector rather than a
>    bare struct iovec
>
> Avi Kivity (5):
>   Add target memory mapping API
>   Add map client retry notification
>   I/O vector helpers
>   Vectored block device API
>   Convert IDE to directly access guest memory
>
>  block.c       |   68 +++++++++++++++++++++++++++
>  block.h       |    8 +++
>  cpu-all.h     |    8 +++
>  cutils.c      |   47 +++++++++++++++++++
>  exec.c        |  142 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  hw/ide.c      |  133 +++++++++++++++++++++++++++++++++++++++++++++++------
>  qemu-common.h |   12 +++++
>  7 files changed, 402 insertions(+), 16 deletions(-)
>
>
>