Olaf Hering wrote:
> 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.
>
Even though cache mode was ignored before, should we now error on
unsupported values?
> 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@xxxxxxxxx>
> ---
> 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;
> + }
>
If the answer to the above is yes, this should be changed to something like
switch (cachemode) {
case VIR_DOMAIN_DISK_CACHE_DEFAULT:
break;
case VIR_DOMAIN_DISK_CACHE_DISABLE:
case VIR_DOMAIN_DISK_CACHE_WRITETHRU:
case VIR_DOMAIN_DISK_CACHE_WRITEBACK:
case VIR_DOMAIN_DISK_CACHE_UNSAFE:
case VIR_DOMAIN_DISK_CACHE_LAST:
error...
break;
case VIR_DOMAIN_DISK_CACHE_DIRECTSYNC:
#if defined(LIBXL_HAVE_DEVICE_DISK_DIRECT_IO_SAFE)
x_disk->direct_io_safe = 1;
#else
error...
#endif
break;
}
Regards,
Jim
> +}
> +
>
> 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;
>
>
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