tools/hotplug: Fix dhcpd symlink removal in vif-nat

Copy temp files used to add/remove dhcpd configurations to avoid
replacing potential symlinks.

If dhcp.conf is a symlink pointing to dhcp.conf.real, using 'mv'
creates a new file dhcp.conf where cp will actually modify
dhcp.conf.real instead of replacing the symlink with a real
file.

Using 'cp' prevents some mistakes where the user will actually
continue to modify dhcp.conf.real where it would not be the one
used anymore.

Signed-off-by: Diego Sueiro <diego.sueiro@arm.com>
Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>
Acked-by: Wei Liu <wl@xen.org>

tools/hotplug/Linux/vif-nat

@@ -95,12 +95,11 @@ dhcparg_remove_entry()
 {
   local tmpfile=$(mktemp)
   sed -e "s/${dev} //" "$dhcpd_arg_file" >"$tmpfile"
-  if diff "$tmpfile" "$dhcpd_arg_file" >/dev/null
+  if ! diff "$tmpfile" "$dhcpd_arg_file" >/dev/null
   then
-    rm "$tmpfile"
-  else
-    mv "$tmpfile" "$dhcpd_arg_file"
+    cp "$tmpfile" "$dhcpd_arg_file"
   fi
+  rm "$tmpfile"
 }
 
 dhcparg_add_entry()
@@ -109,11 +108,11 @@ dhcparg_add_entry()
   local tmpfile=$(mktemp)
   # handle Red Hat, SUSE, and Debian styles, with or without quotes
   sed -e 's/^DHCPDARGS="*\([^"]*\)"*/DHCPDARGS="\1'"${dev} "'"/' \
-     "$dhcpd_arg_file" >"$tmpfile" && mv "$tmpfile" "$dhcpd_arg_file"
+     "$dhcpd_arg_file" >"$tmpfile" && cp "$tmpfile" "$dhcpd_arg_file"
   sed -e 's/^DHCPD_INTERFACE="*\([^"]*\)"*/DHCPD_INTERFACE="\1'"${dev} "'"/' \
-     "$dhcpd_arg_file" >"$tmpfile" && mv "$tmpfile" "$dhcpd_arg_file"
+     "$dhcpd_arg_file" >"$tmpfile" && cp "$tmpfile" "$dhcpd_arg_file"
   sed -e 's/^INTERFACES="*\([^"]*\)"*/INTERFACES="\1'"${dev} "'"/' \
-     "$dhcpd_arg_file" >"$tmpfile" && mv "$tmpfile" "$dhcpd_arg_file"
+     "$dhcpd_arg_file" >"$tmpfile" && cp "$tmpfile" "$dhcpd_arg_file"
   rm -f "$tmpfile"
 }
 
@@ -121,12 +120,11 @@ dhcp_remove_entry()
 {
   local tmpfile=$(mktemp)
   grep -v "host $hostname" "$dhcpd_conf_file" >"$tmpfile"
-  if diff "$tmpfile" "$dhcpd_conf_file" >/dev/null
+  if ! diff "$tmpfile" "$dhcpd_conf_file" >/dev/null
   then
-    rm "$tmpfile"
-  else
-    mv "$tmpfile" "$dhcpd_conf_file"
+    cp "$tmpfile" "$dhcpd_conf_file"
   fi
+  rm "$tmpfile"
   dhcparg_remove_entry
 }