This patch changes the cache= option to accept none, writeback, or writethough
to control the host page cache behavior. By default, writethrough caching is
now used which internally is implemented by using O_DSYNC to open the disk
images. When using -snapshot, writeback is used by default since data integrity
it not at all an issue.
cache=none has the same behavior as cache=off previously. The later syntax is
still supported by now deprecated. I also cleaned up the O_DIRECT
implementation to avoid many of the #ifdefs.
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5485 c046a42c-6fe2-441c-8c8c-71466251a162
This patch refactors the AIO layer to allow multiple AIO implementations. It's
only possible because of the recent signalfd() patch.
Right now, the AIO infrastructure is pretty specific to the block raw backend.
For other block devices to implement AIO, the qemu_aio_wait function must
support registration. This patch introduces a new function,
qemu_aio_set_fd_handler, which can be used to register a file descriptor to be
called back. qemu_aio_wait() now polls a set of file descriptors registered
with this function until one becomes readable or writable.
This patch should allow the implementation of alternative AIO backends (via a
thread pool or linux-aio) and AIO backends in non-traditional block devices
(like NBD).
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5297 c046a42c-6fe2-441c-8c8c-71466251a162
The protocol_name "file" was added to the block driver when async IO was
introduced. This can be used to select that a file is treated as a raw
device instead of probing for the type. However, protocols are not subject
to path interpretation which cases qcow2 images with raw base images to not
function is the path was specified relatively.
The fix is simply to remove the protocol_name from the raw block driver. The
proper way to force the use of a raw block format is to use the format= option
with -drive.
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5233 c046a42c-6fe2-441c-8c8c-71466251a162
Right now, we sprinkle #if defined(QEMU_IMG) && defined(QEMU_NBD) all over the
code. It's ugly and causes us to have to build multiple object files for
linking against qemu and the tools.
This patch introduces a new file, qemu-tool.c which contains enough for
qemu-img, qemu-nbd, and QEMU to all share the same objects.
This also required getting qemu-nbd to be a bit more Windows friendly. I also
changed the Windows block-raw to use normal IO instead of overlapping IO since
we don't actually do AIO yet on Windows. I changed the various #if 0's to
#if WIN32_AIO to make it easier for someone to eventually fix AIO on Windows.
After this patch, there are no longer any #ifdef's related to qemu-img and
qemu-nbd.
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5226 c046a42c-6fe2-441c-8c8c-71466251a162
This patch introduces signalfd() to work around the signal/select race in
checking for AIO completions. For platforms that don't support signalfd(), we
emulate it with threads.
There was a long discussion about this approach. I don't believe there are any
fundamental problems with this approach and I believe eliminating the use of
signals is a good thing.
I've tested Windows and Linux using Windows and Linux guests. I've also checked
for disk IO performance regressions.
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5187 c046a42c-6fe2-441c-8c8c-71466251a162
