[vlanmgr]: Update VLAN removal code to work with 5.10 kernel and newe…

…r iproute2 versions (sonic-net#1970)

* Update VLAN removal code to work with 5.10 kernel and newer iproute2 versions

There is an issue discovered by Alexander Allen where VLAN member
removal from a VLAN doesn't fully happen on a 5.10 kernel. The reason
for this is that there is a change in the output of the `bridge vlan
show` command between the 4.19 kernel and the 5.10 kernel. To add to
this, the output is different depending on whether iproute2 4.20 or
iproute2 5.10 is installed. These output changes cause only some of the
VLAN member removal code to run; specifically, the interface will not be
the member of a VLAN anymore, but it will still be part of the bridge.

Therefore, update the code that parses the output of `bridge vlan show`
to handle iproute2 4.20 with 4.19 kernel, iproute2 4.20 with 5.10
kernel, and iproute2 5.10 with 5.10 kernel. This should cover all
possible combinations we'll have until all containers are on Bullseye.

Signed-off-by: Saikrishna Arcot <sarcot@microsoft.com>

* Store the exit code of the bridge vlan show command.

Signed-off-by: Saikrishna Arcot <sarcot@microsoft.com>

* Add missing space.

Signed-off-by: Saikrishna Arcot <sarcot@microsoft.com>

cfgmgr/vlanmgr.cpp

@@ -237,19 +237,27 @@ bool VlanMgr::removeHostVlanMember(int vlan_id, const string &port_alias)
 
     // The command should be generated as:
     // /bin/bash -c '/sbin/bridge vlan del vid {{vlan_id}} dev {{port_alias}} &&
-    //               ( /sbin/bridge vlan show dev {{port_alias}} | /bin/grep -q None;
-    //               ret=$?; if [ $ret -eq 0 ]; then
+    //               ( vlanShow=$(/sbin/bridge vlan show dev {{port_alias}});
+    //               ret=$?;
+    //               if [ $ret -eq 0 ]; then
+    //               if (! echo "$vlanShow" | grep -q {{port_alias}})
+    //                 || (echo "$vlanShow" | grep -q None$)
+    //                 || (echo "$vlanShow" | grep -q {{port_alias}}$); then
     //               /sbin/ip link set {{port_alias}} nomaster;
-    //               elif [ $ret -eq 1 ]; then exit 0;
+    //               fi;
     //               else exit $ret; fi )'
 
     // When port is not member of any VLAN, it shall be detached from Dot1Q bridge!
     ostringstream cmds, inner;
     inner << BRIDGE_CMD " vlan del vid " + std::to_string(vlan_id) + " dev " << shellquote(port_alias) << " && ( "
-      BRIDGE_CMD " vlan show dev " << shellquote(port_alias) << " | "
-      GREP_CMD " -q None; ret=$?; if [ $ret -eq 0 ]; then "
+      "vlanShow=$(" BRIDGE_CMD " vlan show dev " << shellquote(port_alias) << "); "
+      "ret=$?; "
+      "if [ $ret -eq 0 ]; then "
+      "if (! echo \"$vlanShow\" | " GREP_CMD " -q " << shellquote(port_alias) << ") "
+      " || (echo \"$vlanShow\" | " GREP_CMD " -q None$) "
+      " || (echo \"$vlanShow\" | " GREP_CMD " -q " << shellquote(port_alias) << "$); then "
       IP_CMD " link set " << shellquote(port_alias) << " nomaster; "
-      "elif [ $ret -eq 1 ]; then exit 0; "
+      "fi; "
       "else exit $ret; fi )";
     cmds << BASH_CMD " -c " << shellquote(inner.str());