krun: parse annotations for krun.{cpus, ram_mib}

Support the use of OCI annotations as a way for the container engine to
configure the microVM's CPU count and RAM amount via `krun.cpus` and
`krun.ram_mib` respectively.

Signed-off-by: Jake Correnti <jakecorrenti+github@proton.me>

Author: jakecorrenti

src/libcrun/handlers/krun.c

@@ -184,42 +184,85 @@ libkrun_read_vm_config (yajl_val *config_tree, libcrun_error_t *err)
   return 0;
 }
 
+/*
+ * Default to parsing the OCI annotations to find the specified resource
+ * metadata. If the provided value not a non-negative integer, then fallback to
+ * the provided default value. If the annotation is not provided, parse the
+ * krun_vm.json file. If the value provided in the krun_vm.json file is not a
+ * non-negative integer, or if the krun_vm.json file also doesn't contain the
+ * metadata, then fallback to the default value provided.
+ */
+static int
+libkrun_parse_resource_configuration (yajl_val *config_tree, libcrun_container_t *container, const char *annotation, const char *path[], int default_val)
+{
+  char *annotation_val;
+  char *endptr;
+  int resource_val = default_val;
+  yajl_val krun_file_val = NULL;
+
+  annotation_val = (char *) find_annotation (container, annotation);
+  if (annotation_val != NULL)
+    {
+      errno = 0;
+      resource_val = (int) strtol (annotation_val, &endptr, 10);
+      if (errno != 0 || endptr == annotation_val || *endptr != '\0')
+        {
+          // annotations input is not an integer
+          return default_val;
+        }
+    }
+  else if (*config_tree != NULL)
+    {
+      krun_file_val = yajl_tree_get (*config_tree, path, yajl_t_number);
+      if (! YAJL_IS_INTEGER (krun_file_val))
+        {
+          return default_val;
+        }
+
+      if (krun_file_val != NULL)
+        resource_val = (int) YAJL_GET_INTEGER (krun_file_val);
+    }
+
+  if (resource_val < 1)
+    {
+      // parsed value is non-positive
+      return default_val;
+    }
+
+  return resource_val;
+}
+
 static int
-libkrun_configure_vm (uint32_t ctx_id, void *handle, bool *configured, yajl_val *config_tree, libcrun_error_t *err)
+libkrun_configure_vm (uint32_t ctx_id, void *handle, bool *configured, yajl_val *config_tree, libcrun_container_t *container, libcrun_error_t *err)
 {
   int32_t (*krun_set_vm_config) (uint32_t ctx_id, uint8_t num_vcpus, uint32_t ram_mib);
-  yajl_val cpus = NULL;
-  yajl_val ram_mib = NULL;
+  int cpus, ram_mib, ret;
   const char *path_cpus[] = { "cpus", (const char *) 0 };
   const char *path_ram_mib[] = { "ram_mib", (const char *) 0 };
-  int ret;
-
-  if (*config_tree == NULL)
-    return 0;
-
-  /* Try to configure an external kernel. If the configuration file doesn't
-   * specify a kernel, libkrun automatically fall back to using libkrunfw,
-   * if the library is present and was loaded while creating the context.
-   */
-  ret = libkrun_configure_kernel (ctx_id, handle, config_tree, err);
-  if (UNLIKELY (ret))
-    return ret;
 
-  cpus = yajl_tree_get (*config_tree, path_cpus, yajl_t_number);
-  ram_mib = yajl_tree_get (*config_tree, path_ram_mib, yajl_t_number);
-  /* Both cpus and ram_mib must be present at the same time */
-  if (cpus == NULL || ram_mib == NULL || ! YAJL_IS_INTEGER (cpus) || ! YAJL_IS_INTEGER (ram_mib))
-    return 0;
+  cpus = libkrun_parse_resource_configuration (config_tree, container, "krun.cpus", path_cpus, 1);
+  ram_mib = libkrun_parse_resource_configuration (config_tree, container, "krun.ram_mib", path_ram_mib, 1024);
 
   krun_set_vm_config = dlsym (handle, "krun_set_vm_config");
 
   if (krun_set_vm_config == NULL)
     return crun_make_error (err, 0, "could not find symbol in the krun library");
 
-  ret = krun_set_vm_config (ctx_id, YAJL_GET_INTEGER (cpus), YAJL_GET_INTEGER (ram_mib));
+  ret = krun_set_vm_config (ctx_id, cpus, ram_mib);
   if (UNLIKELY (ret < 0))
     return crun_make_error (err, -ret, "could not set krun vm configuration");
 
+  if (*config_tree != NULL)
+    {
+      /* Try to configure an external kernel. If the configuration file doesn't
+       * specify a kernel, libkrun automatically fall back to using libkrunfw,
+       * if the library is present and was loaded while creating the context.
+       */
+      ret = libkrun_configure_kernel (ctx_id, handle, config_tree, err);
+      if (UNLIKELY (ret))
+        return ret;
+    }
+
   *configured = true;
 
   return 0;
@@ -395,7 +438,7 @@ libkrun_exec (void *cookie, libcrun_container_t *container, const char *pathname
         error (EXIT_FAILURE, -ret, "could not set enclave execution arguments");
     }
 
-  ret = libkrun_configure_vm (ctx_id, handle, &configured, &config_tree, &err);
+  ret = libkrun_configure_vm (ctx_id, handle, &configured, &config_tree, container, &err);
   if (UNLIKELY (ret))
     {
       libcrun_error_t *tmp_err = &err;