custom-env: Add support for argument array

execve() takes the same form for arguments as environment: an array of
constant pointers to mutable strings, terminated by a NULL.

To make it easier for users who want to build up their own argument
strings to pass to execve, add support for argument arrays to custom_env.

Signed-off-by: Daniel Stone <daniels@collabora.com>

shared/process-util.c

@@ -78,6 +78,8 @@ custom_env_init_from_environ(struct custom_env *env)
 
 	wl_array_init(&env->envp);
 	env->env_finalized = false;
+	wl_array_init(&env->argp);
+	env->arg_finalized = false;
 
 	for (it = environ; *it; it++) {
 		ep = wl_array_add(&env->envp, sizeof *ep);
@@ -94,8 +96,11 @@ custom_env_fini(struct custom_env *env)
 
 	wl_array_for_each(p, &env->envp)
 		free(*p);
-
 	wl_array_release(&env->envp);
+
+	wl_array_for_each(p, &env->argp)
+		free(*p);
+	wl_array_release(&env->argp);
 }
 
 static char **
@@ -116,6 +121,20 @@ custom_env_get_env_var(struct custom_env *env, const char *name)
 	return NULL;
 }
 
+void
+custom_env_add_arg(struct custom_env *env, const char *arg)
+{
+	char **ap;
+
+	assert(!env->arg_finalized);
+
+	ap = wl_array_add(&env->argp, sizeof *ap);
+	assert(ap);
+
+	*ap = strdup(arg);
+	assert(*ap);
+}
+
 void
 custom_env_set_env_var(struct custom_env *env, const char *name, const char *value)
 {
@@ -151,3 +170,20 @@ custom_env_get_envp(struct custom_env *env)
 
 	return env->envp.data;
 }
+
+char *const *
+custom_env_get_argp(struct custom_env *env)
+{
+	char **ap;
+
+	assert(!env->arg_finalized);
+
+	/* add terminating NULL */
+	ap = wl_array_add(&env->argp, sizeof *ap);
+	assert(ap);
+	*ap = NULL;
+
+	env->arg_finalized = true;
+
+	return env->argp.data;
+}

shared/process-util.h

@@ -61,13 +61,15 @@ fdstr_close_all(struct fdstr *s);
 
 
 /**
- * A container for environment variables, designed to be used when forking child
- * processes, as setenv() and anything which allocates memory cannot be used
- * between fork() and exec().
+ * A container for environment variables and/or process arguments, designed to
+ * be used when forking child processes, as setenv() and anything which
+ * allocates memory cannot be used between fork() and exec().
  */
 struct custom_env {
 	struct wl_array envp;
 	bool env_finalized;
+	struct wl_array argp;
+	bool arg_finalized;
 };
 
 void
@@ -79,5 +81,11 @@ custom_env_fini(struct custom_env *env);
 void
 custom_env_set_env_var(struct custom_env *env, const char *name, const char *value);
 
+void
+custom_env_add_arg(struct custom_env *env, const char *arg);
+
 char *const *
 custom_env_get_envp(struct custom_env *env);
+
+char *const *
+custom_env_get_argp(struct custom_env *env);