[Qemu-devel] [PATCH 0/2] ide: convert pio code path to asynchronous I/O

[Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>]

IDE PIO mode is currently implemented using synchronous I/O functions.  There's
no need to do this because the IDE interface is actually designed with polling
and interrupts in mind - we can do asynchronous I/O and let the guest know when
the operation has completed.  The benefit of asynchronous I/O is that the guest
can continue executing code and is more responsive.

The second aim of this conversion is to avoid calling bdrv_read()/bdrv_write()
since they do not work with I/O throttling.  This means guests should now boot
IDE drives successfully when I/O throttling is enabled.

Note that ATAPI is not converted yet and still uses bdrv_read() in two
locations.  A future patch will have to convert ATAPI so CD-ROMs also do
asynchronous I/O.

I have tested both Windows 7 Home Premium and Red Hat Enterprise Linux 6.0
guests with these patches.  In Windows, use the device manager to disable DMA
on the IDE channels.  Under recent Linux kernels, use the libata.dma=0 kernel
parameter.

Chris and Richard: Please test this to confirm that it fixes the hang you
reported.

Stefan Hajnoczi (2):
  ide: convert ide_sector_read() to asynchronous I/O
  ide: convert ide_sector_write() to asynchronous I/O

 hw/ide/core.c     |  129 ++++++++++++++++++++++++++++++++++++----------------
 hw/ide/internal.h |    2 +
 2 files changed, 91 insertions(+), 40 deletions(-)

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1.7.9.1