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

[Avi Kivity]

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.

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(-)