dm: script: enable discard feature for virtio-blk

To support discard for virtio-blk, the backend file should also located
in a filesystem which support discard. So, mount /data partition with '
-o discard'.
Then, add 'discard' to virtio-blk to enable this feature.

1. Erase operations on UOS will trigger the discard on SOS instead of
writing zero, which will save erase time.

2. Discard in storage firmware will move the mapped host address range to
the unmapped host address range. So, when delete a file in UOS, discard
will trigger the space collection on storage, so that in the next write
operation, it need not to do erase first.

Tracked-On: #2547
Signed-off-by: Conghui Chen <conghui.chen@intel.com>
Reviewed-by: Yu Wang <yu1.wang@intel.com>
Acked-by: Binbin Wu <binbin.wu@intel.com>

devicemodel/samples/apl-mrb/launch_uos.sh

@@ -151,7 +151,7 @@ acrn-dm -A -m $mem_size -c $2$boot_GVT_option"$GVT_args" -s 0:0,hostbridge -s 1:
   -s 5,virtio-console,@pty:pty_port \
   -s 6,virtio-hyper_dmabuf \
   -s 8,wdt-i6300esb \
-  -s 3,virtio-blk$boot_dev_flag,/data/$5/$5.img \
+  -s 3,virtio-blk$boot_dev_flag,/data/$5/$5.img,discard \
   -s 4,virtio-net,$tap $boot_image_option \
   -s 7,xhci,1-1:1-2:1-3:2-1:2-2:2-3:cap=apl \
   -s 9,passthru,0/15/1 \
@@ -352,7 +352,7 @@ echo "dm_run: after passthru dev preparing" > /dev/kmsg
 
  acrn-dm -A -m $mem_size -c $2$boot_GVT_option"$GVT_args" -s 0:0,hostbridge -s 1:0,lpc -l com1,stdio $npk_virt\
    -s 9,virtio-net,$tap \
-   -s 3,virtio-blk$boot_dev_flag,/data/$5/$5.img \
+   -s 3,virtio-blk$boot_dev_flag,/data/$5/$5.img,discard \
    -s 7,xhci,1-1:1-2:1-3:2-1:2-2:2-3:cap=apl \
    -s 8,passthru,0/15/1 \
    -s 13,virtio-rpmb \
@@ -424,7 +424,7 @@ if [ ! -b "/dev/mmcblk1p3" ]; then
 fi
 
 mkdir -p /data
-mount /dev/mmcblk1p3 /data
+mount -o discard /dev/mmcblk1p3 /data
 
 if [ $launch_type == 6 ]; then
 	if [ -f "/data/android/android.img" ]; then