container: T7185: Allow tmpfs mounts within containers

Author: Embezzle

interface-definitions/container.xml.in

@@ -412,6 +412,31 @@
               </constraint>
             </properties>
           </leafNode>
+          <tagNode name="tmpfs">
+            <properties>
+              <help>Mount a tmpfs filesystem into the container</help>
+            </properties>
+            <children>
+              <leafNode name="destination">
+                <properties>
+                  <help>Destination container directory</help>
+                  <valueHelp>
+                    <format>txt</format>
+                    <description>Destination container directory</description>
+                  </valueHelp>
+                </properties>
+              </leafNode>
+              <leafNode name="size">
+                <properties>
+                  <help>Filesystem size in MB</help>
+                  <valueHelp>
+                    <format>u32</format>
+                    <description>Filesystem size in MB</description>
+                  </valueHelp>
+                </properties>
+              </leafNode>
+            </children>
+          </tagNode>
           <tagNode name="volume">
             <properties>
               <help>Mount a volume into the container</help>

src/conf_mode/container.py

@@ -223,6 +223,13 @@ def verify(container):
                     if not os.path.exists(source):
                         raise ConfigError(f'Volume "{volume}" source path "{source}" does not exist!')
 
+            if 'tmpfs' in container_config:
+                for tmpfs, tmpfs_config in container_config['tmpfs'].items():
+                    if 'destination' not in tmpfs_config:
+                        raise ConfigError(f'tmpfs "{tmpfs}" has no destination path configured!')
+                    if 'size' not in tmpfs_config:
+                        raise ConfigError(f'tmpfs "{tmpfs}" has no size configured!')
+
             if 'port' in container_config:
                 for tmp in container_config['port']:
                     if not {'source', 'destination'} <= set(container_config['port'][tmp]):
@@ -362,6 +369,14 @@ def generate_run_arguments(name, container_config):
             prop = vol_config['propagation']
             volume += f' --volume {svol}:{dvol}:{mode},{prop}'
 
+    # Mount tmpfs
+    tmpfs = ''
+    if 'tmpfs' in container_config:
+        for tmpfs_config in container_config['tmpfs'].values():
+            dest = tmpfs_config['destination']
+            size = tmpfs_config['size']
+            tmpfs += f' --mount=type=tmpfs,tmpfs-size={size}M,destination={dest}'
+
     host_pid = ''
     if 'allow_host_pid' in container_config:
       host_pid = '--pid host'
@@ -373,7 +388,7 @@ def generate_run_arguments(name, container_config):
 
     container_base_cmd = f'--detach --interactive --tty --replace {capabilities} --cpus {cpu_quota} {sysctl_opt} ' \
                          f'--memory {memory}m --shm-size {shared_memory}m --memory-swap 0 --restart {restart} ' \
-                         f'--name {name} {hostname} {device} {port} {name_server} {volume} {env_opt} {label} {uid} {host_pid}'
+                         f'--name {name} {hostname} {device} {port} {name_server} {volume} {tmpfs} {env_opt} {label} {uid} {host_pid}'
 
     entrypoint = ''
     if 'entrypoint' in container_config: