tests: Cover vfs_iterate_mount_dirs in a new test

... adding precision to the documentation where a corner case was
discovered during testing and is permitted.

The test is too large for one small board, just like the other existing
VFS test.

sys/include/vfs.h

@@ -1014,8 +1014,8 @@ const vfs_mount_t *vfs_iterate_mounts(const vfs_mount_t *cur);
  * access to the mount point's stats through @ref vfs_dstatvfs. If mounts or
  * unmounts happen while iterating, this is guaranteed to report all file
  * systems that stayed mounted, and may report any that are transiently
- * mounted. Note that the volume being reported can not be unmounted as @p dir
+ * mounted for up to as often as they are (re)mounted. Note that the volume
- * is an open directory.
+ * being reported can not be unmounted as @p dir is an open directory.
  *
  * Zero-initialize @p dir to start. As long as @c true is returned, @p dir is a
  * valid directory on which the user can call @ref vfs_readdir or @ref

tests/vfs_iterate_mount/Makefile

@@ -0,0 +1,6 @@
+include ../Makefile.tests_common
+
+USEMODULE += vfs
+USEMODULE += constfs
+
+include $(RIOTBASE)/Makefile.include

tests/vfs_iterate_mount/Makefile.ci

@@ -0,0 +1,3 @@
+BOARD_INSUFFICIENT_MEMORY := \
+    nucleo-l011k4 \
+    #

tests/vfs_iterate_mount/main.c

@@ -0,0 +1,124 @@
+/*
+ * Copyright (C) Christian Amsüss <chrysn@fsfe.org>
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * Mount and unmount a few file systems, demonstrating that
+ * vfs_iterate_mount_dirs performs as advertised.
+ *
+ * @author      Christian Amsüss <chrysn@fsfe.org>
+ */
+
+#include <stdio.h>
+#include <assert.h>
+#include <string.h>
+
+#include <vfs.h>
+#include <fs/constfs.h>
+
+static constfs_file_t constfs_files[1] = {
+    /* Not completely empty -- that'd be a hassle around empty arrays and
+     * their size */
+    {
+        .path = "some-file",
+        .size = 0,
+        .data = (void*)"",
+    },
+};
+
+static constfs_t constfs_desc = {
+    .nfiles = ARRAY_SIZE(constfs_files),
+    .files = constfs_files,
+};
+
+static vfs_mount_t mount1 = {
+    .fs = &constfs_file_system,
+    .mount_point = "/const1",
+    .private_data = &constfs_desc,
+};
+
+static vfs_mount_t mount2 = {
+    .fs = &constfs_file_system,
+    .mount_point = "/const2",
+    .private_data = &constfs_desc,
+};
+
+static vfs_mount_t mount3 = {
+    .fs = &constfs_file_system,
+    .mount_point = "/const3",
+    .private_data = &constfs_desc,
+};
+
+static vfs_mount_t mount4 = {
+    .fs = &constfs_file_system,
+    .mount_point = "/const4",
+    .private_data = &constfs_desc,
+};
+
+/* Crank the iterator, reporting "N%s" for the next entry, or "O\n" for the end
+ * of the iterator (avoiding the letter "E" which may be misread for an error
+ * in a casual look at the error output) */
+static void iter_and_report(vfs_DIR *iter) {
+    bool result = vfs_iterate_mount_dirs(iter);
+    if (result) {
+        printf("N(%s)", iter->mp->mount_point);
+    } else {
+        printf("O\n");
+        /* Zero out so we're ready for next round immediately */
+        memset(iter, 0, sizeof(*iter));
+    }
+}
+
+int main(void) {
+    int res = 0;
+
+    vfs_DIR iter;
+    memset(&iter, 0, sizeof(iter));
+
+    res |= vfs_mount(&mount1);
+    res |= vfs_mount(&mount2);
+    res |= vfs_mount(&mount3);
+    res |= vfs_mount(&mount4);
+    assert(res == 0);
+    printf("Mounted 1234\n");
+
+    /* N1N2N3N4E */
+    iter_and_report(&iter);
+    iter_and_report(&iter);
+    iter_and_report(&iter);
+    iter_and_report(&iter);
+    iter_and_report(&iter);
+
+    /* N1N2, unmount 3, N4E */
+    iter_and_report(&iter);
+    iter_and_report(&iter);
+    res |= vfs_umount(&mount3);
+    iter_and_report(&iter);
+    iter_and_report(&iter);
+
+    /* N1, unmount 2, (3 is already unmounted), N4, mount 3 N3, unmount 1 and remount it at the end N1, O */
+    /* It is OK that 1 is reported twice, because its first occurrence is its
+     * old mounting, and later it reappears */
+    iter_and_report(&iter);
+    res |= vfs_umount(&mount2);
+    iter_and_report(&iter);
+    res |= vfs_mount(&mount3);
+    iter_and_report(&iter);
+    res |= vfs_umount(&mount1);
+    res |= vfs_mount(&mount1);
+    iter_and_report(&iter);
+    iter_and_report(&iter);
+
+    /* This ensures we're not leaking locks */
+    res |= vfs_umount(&mount1);
+    res |= vfs_umount(&mount3);
+    res |= vfs_umount(&mount4);
+    printf("All unmounted\n");
+
+    /* Only O */
+    iter_and_report(&iter);
+}

tests/vfs_iterate_mount/tests/01-run.py

@@ -0,0 +1,23 @@
+#!/usr/bin/env python3
+
+# Copyright (C) 2021 Christian Amsüss <chrysn@fsfe.org>
+#
+# This file is subject to the terms and conditions of the GNU Lesser
+# General Public License v2.1. See the file LICENSE in the top level
+# directory for more details.
+
+import sys
+from testrunner import run
+
+
+def testfunc(child):
+    child.expect_exact("Mounted 1234")
+    child.expect_exact("N(/const1)N(/const2)N(/const3)N(/const4)O")
+    child.expect_exact("N(/const1)N(/const2)N(/const4)O")
+    child.expect_exact("N(/const1)N(/const4)N(/const3)N(/const1)O")
+    child.expect_exact("All unmounted")
+    child.expect_exact("O")
+
+
+if __name__ == "__main__":
+    sys.exit(run(testfunc))