Supporting "docker exec" in Genv container toolkit

genv-docker/README.md

@@ -120,4 +120,5 @@ Use non available devices if needed when set to `1`.
 3. https://github.com/opencontainers/runtime-spec/blob/main/glossary.md
 4. https://github.com/opencontainers/runc/blob/main/man/runc.8.md
 5. https://github.com/opencontainers/runc/blob/main/man/runc-create.8.md
-6. https://github.com/NVIDIA/nvidia-container-runtime
+6. https://github.com/opencontainers/runc/blob/main/man/runc-exec.8.md
+7. https://github.com/NVIDIA/nvidia-container-runtime

genv-docker/genv-container-runtime.py

@@ -21,38 +21,59 @@ def find_container_runtime() -> str:
     raise RuntimeError("Cannot find any container runtime")
 
 
-def get_env(config: dict, name: str) -> Optional[str]:
+def get_env(process: dict, name: str) -> Optional[str]:
     """
     Returns the value of an environment variable if set.
     """
 
-    for env in config["process"]["env"]:
+    for env in process["env"]:
         if env.startswith(f"{name}="):
             return env.split("=")[-1]
 
 
-def append_env(config: dict, name: str, value: str) -> None:
+def append_env(process: dict, name: str, value: str) -> None:
     """
     Appends an environment variable to the configuration.
     """
 
-    config["process"]["env"].append(f"{name}={value}")
+    process["env"].append(f"{name}={value}")
 
 
-def update_env(config: dict, name: str, mutator: Callable[[str], str]) -> None:
+def update_env(process: dict, name: str, mutator: Callable[[str], str]) -> None:
     """
     Updates an environment variable.
     """
 
-    for index, env in enumerate(config["process"]["env"]):
+    for index, env in enumerate(process["env"]):
         if env.startswith(f"{name}="):
             value = env.split("=")[-1]
-            config["process"]["env"][index] = f"{name}={mutator(value)}"
+            process["env"][index] = f"{name}={mutator(value)}"
             return
 
     raise RuntimeError(f"Cannot update environment variable '{name}'")
 
 
+def update_process(process: dict, container_id: str) -> None:
+    """Updates a process json object.
+
+    References:
+    - https://github.com/opencontainers/runtime-spec/blob/main/config.md#process
+    """
+
+    append_env(process, "GENV_CONTAINER", "1")
+
+    if not get_env(process, "GENV_ACTIVATE") == "0":
+        if not get_env(process, "GENV_ENVIRONMENT_ID"):
+            # TODO(raz): consider generating an environment identifier which is different than
+            # the container identifier to avoid this kind of information leak.
+            # also note that a short version of the container identifier is set as the container
+            # hostname then it might be ok.
+            append_env(process, "GENV_ENVIRONMENT_ID", container_id)
+
+    if not get_env(process, "GENV_MOUNT_SHIMS") == "0":
+        update_env(process, "PATH", lambda value: f"/opt/genv/shims:{value}")
+
+
 def append_hook(
     config: dict,
     type: str,
@@ -92,18 +113,7 @@ def do_create(container_id: str) -> None:
     with open("config.json") as f:
         config = json.load(f)
 
-    append_env(config, "GENV_CONTAINER", "1")
-
-    if not get_env(config, "GENV_ACTIVATE") == "0":
-        if not get_env(config, "GENV_ENVIRONMENT_ID"):
-            # TODO(raz): consider generating an environment identifier which is different than
-            # the container identifier to avoid this kind of information leak.
-            # also note that a short version of the container identifier is set as the container
-            # hostname then it might be ok.
-            append_env(config, "GENV_ENVIRONMENT_ID", container_id)
-
-    if not get_env(config, "GENV_MOUNT_SHIMS") == "0":
-        update_env(config, "PATH", lambda value: f"/opt/genv/shims:{value}")
+    update_process(config["process"], container_id)
 
     # NOTE(raz): even though the hook "prestart" is deprecated, we are using it because the
     # nvidia container runtime still uses it itself and we need to make sure we will run before.
@@ -119,9 +129,27 @@ def do_create(container_id: str) -> None:
         json.dump(config, f)
 
 
+def do_exec(process_json: str, container_id: str) -> None:
+    """
+    Performs the command 'exec'.
+    """
+
+    with open(process_json) as f:
+        process = json.load(f)
+
+    update_process(process, container_id)
+
+    with open(process_json, "w") as f:
+        json.dump(process, f)
+
+
 # TODO(raz): prettify error messages
 if __name__ == "__main__":
     if "create" in sys.argv:
         do_create(container_id=sys.argv[-1])
-
+    elif "exec" in sys.argv:
+        do_exec(
+            process_json=sys.argv[sys.argv.index("--process") + 1],
+            container_id=sys.argv[-1],
+        )
     subprocess.check_call([find_container_runtime()] + sys.argv[1:])