1. support "writeback" and "writethru" mode toggling for virtio-blk
conditionally. When starting DM with "writethru" parameter in
virtio-blk, guest OS could not toggle cache mode. When starting DM
with "writeback" parameter in virtio-blk, guest OS could toggle
cache mode.
------------------------------
DM cmdline | toggle support
------------+-----------------
writeback | yes
writethru | no
------------------------------
2. To toggle cache mode, run below command in guest OS:
echo "write back" > /sys/devices/xxx/vdx/cache_type
OR
echo "write through" > /sys/devices/xxx/vdx/cache_type
Signed-off-by: Conghui Chen <conghui.chen@intel.com>
Reviewed-by: Shuo Liu <shuo.a.liu@intel.com>
Acked-by: Yin Fengwei <fengwei.yin@intel.com>
Conghui Chen