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

From: Avi Kivity
Subject: [Qemu-devel] [PATCH 0/5] Direct memory access for devices
Date: Sun, 18 Jan 2009 21:53:14 +0200

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.

Avi Kivity (5):
  Add target memory mapping API
  Add map client retry notification
  Vectored block device API
  I/O vector helpers
  Convert IDE to directly access guest memory

 block.c       |   92 ++++++++++++++++++++++++++++++++++++++++
 block.h       |    7 +++
 cpu-all.h     |    8 ++++
 exec.c        |  131 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 hw/ide.c      |  127 +++++++++++++++++++++++++++++++++++++++++++++++++------
 qemu-common.h |   10 ++++
 vl.c          |   25 +++++++++++
 7 files changed, 386 insertions(+), 14 deletions(-)

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