Up to now xend and libxl did not have any way and need to specify a cache= mode for block devices. At least the libxl driver did just ignore the cachemode value. With xen-4.5 a new knob was added to libxl which instructs qemu to use threads=native cache=directsync in the qdisk driver. This mode was disabled early due to a pvops kernel bug. As a workaround cache=writeback was set as default. The kernel bug is long fixed. I assume the forward ported xenlinux kernel never had this bug. This change exposes the knob to libvirt. If cache=directsync is set qemu is instructed to use native AIO. This change also lays the ground work to set cache=unsafe at some point. It is currently under investigation whether libxl should expose such knob. Signed-off-by: Olaf Hering <olaf(a)aepfle.de&gt; --- src/libxl/libxl_conf.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/src/libxl/libxl_conf.c b/src/libxl/libxl_conf.c index 4cb062e..79f4a82 100644 --- a/src/libxl/libxl_conf.c +++ b/src/libxl/libxl_conf.c @@ -739,6 +739,20 @@ libxlDiskSetDiscard(libxl_device_disk *x_disk, int discard) #endif } +static void +libxlDiskSetCacheMode(libxl_device_disk *x_disk, int cachemode) +{ + switch (cachemode) { +#if defined(LIBXL_HAVE_DEVICE_DISK_DIRECT_IO_SAFE) + case VIR_DOMAIN_DISK_CACHE_DIRECTSYNC: + x_disk->direct_io_safe = 1; + break; +#endif + default: + break; + } +} + int libxlMakeDisk(virDomainDiskDefPtr l_disk, libxl_device_disk *x_disk) @@ -855,6 +869,7 @@ libxlMakeDisk(virDomainDiskDefPtr l_disk, libxl_device_disk *x_disk) x_disk->readwrite = !l_disk->readonly; x_disk->is_cdrom = l_disk->device == VIR_DOMAIN_DISK_DEVICE_CDROM ? 1 : 0; libxlDiskSetDiscard(x_disk, l_disk->discard); + libxlDiskSetCacheMode(x_disk, l_disk->cachemode); /* An empty CDROM must have the empty format, otherwise libxl fails. */ if (x_disk->is_cdrom && !x_disk->pdev_path) x_disk->format = LIBXL_DISK_FORMAT_EMPTY;