[multi-asic][vs]: Update readme file to create multi-asic vs

platform/vs/README.vsvm.md

@@ -23,8 +23,42 @@ virsh #
 ```
 
 2. Create SONiC VM for multi-ASIC HWSKU
-Update sonic_multiasic.xml with the external interfaces 
-required for HWSKU.
+
+- Based on the number of asics of hwsku, update device/x86_64-kvm_x86_64-r0/asic.conf 
+```
+NUM_ASIC=<n>
+DEV_ID_ASIC_0=0
+DEV_ID_ASIC_1=1
+DEV_ID_ASIC_2=2
+DEV_ID_ASIC_3=3
+..
+DEV_ID_ASIC_<n-1>=<n-1>
+```
+For example, a four asic VS asic.conf will be:
+```
+NUM_ASIC=4
+DEV_ID_ASIC_0=0
+DEV_ID_ASIC_1=1
+DEV_ID_ASIC_2=2
+DEV_ID_ASIC_3=3
+```
+- Create a topology.sh script which will create the internal asic topology for
+the specific hwsku.
+For example, for msft_multi_asic_vs:
+https://github.com/Azure/sonic-buildimage/blob/master/device/virtual/x86_64-kvm_x86_64-r0/msft_multi_asic_vs/topology.sh
+
+- With the updated asic.conf and topology.sh, build sonic-vs.img which can be used to 
+bring up multi-asic virtual switch.
+
+- Update platform/vs/sonic_multiasic.xml with higher memory and vcpu as required.
+  - For 4-asic vs platform msft_four_asic_vs hwsku, 8GB memory and 10vCPUs.
+  - For 7-ASIC vs platform msft_multi_asic_vs hwsku, 8GB and 16vCPUs.
+- Update the number of front-panel interfaces in sonic_multliasic.xml
+    - For 4-ASIC vs platform, 8 front panel interfaces.
+    - For 6-ASIC vs platform, 64 front panel interfaces.
+
+- With multi-asic sonic_vs.img and sonic_multiasic.xml file, bring up multi-asic
+vs as:
 
 ```
 $ sudo virsh
@@ -38,18 +72,25 @@ virsh # create sonic_multiasic.xml
 Domain sonic created from sonic.xml
 
 virsh #
+```
+
+- Steps to convert a prebuilt single asic sonic-vs.img:
+  - Use the updated sonic_multiasic.xml file and bring up virtual switch.
+  - Update /usr/share/sonic/device/x86_64-kvm_x86_64-r0/asic.conf as above.
+  - Add topology.sh in /usr/share/sonic/device/x86_64-kvm_x86_64-r0/<HWSKU>
+  - stop database service and remove database docker, so that when vs is 
+rebooted, database_global.json is created with the right namespaces.
+    - systemctl stop database
+    - docker rm database
+  - sudo reboot
+  - Once rebooted, VS should be multi-asic VS.
+
+- Start topology service.
+```
+sudo systemctl start topology.
+```
 
-Once booted up, create a file "asic.conf" with the content:
-NUM_ASIC=<Number of asics>
-under /usr/share/sonic/device/x86_64-kvm_x86_64-r0/
-Also, create a "topology.sh" file which will simulate the internal
-asic connectivity of the hardware under
-/usr/share/sonic/device/x86_64-kvm_x86_64-r0/<HWSKU>
-The HWSKU directory will have the required files like port_config.ini
-for each ASIC.
-
-Having done this, a new service "topology.service" will be started
-during bootup which will invoke topology.sh script.
+- Load configuration using minigraph or config_dbs.
 
 3. Access virtual switch: