diff --git a/main.c b/main.c
index 78148f2cb019c..d7f3c7aaf1bce 100644
--- a/main.c
+++ b/main.c
@@ -211,14 +211,22 @@ static void start_mp(safe_mode_t safe_mode) {
 
 static void stop_mp(void) {
     #if MICROPY_VFS
-    mp_vfs_mount_t *vfs = MP_STATE_VM(vfs_mount_table);
 
     // Unmount all heap allocated vfs mounts.
-    while (gc_ptr_on_heap(vfs)) {
+    mp_vfs_mount_t *vfs = MP_STATE_VM(vfs_mount_table);
+    do {
+        if (gc_ptr_on_heap(vfs)) {
+            // mp_vfs_umount will splice out an unmounted vfs from the vfs_mount_table linked list.
+            mp_vfs_umount(vfs->obj);
+            // Start over at the beginning of the list since the first entry may have been removed.
+            vfs = MP_STATE_VM(vfs_mount_table);
+            continue;
+        }
         vfs = vfs->next;
-    }
-    MP_STATE_VM(vfs_mount_table) = vfs;
+    } while (vfs != NULL);
+
     // The last vfs is CIRCUITPY and the root directory.
+    vfs = MP_STATE_VM(vfs_mount_table);
     while (vfs->next != NULL) {
         vfs = vfs->next;
     }
diff --git a/ports/atmel-samd/boards/circuitbrains_basic_m0/mpconfigboard.mk b/ports/atmel-samd/boards/circuitbrains_basic_m0/mpconfigboard.mk
index 7c301e3ea9692..121becc472d36 100755
--- a/ports/atmel-samd/boards/circuitbrains_basic_m0/mpconfigboard.mk
+++ b/ports/atmel-samd/boards/circuitbrains_basic_m0/mpconfigboard.mk
@@ -11,4 +11,5 @@ EXTERNAL_FLASH_DEVICES = "W25Q32JVxQ"
 LONGINT_IMPL = MPZ
 
 CIRCUITPY_CODEOP = 0
-CIRCUITPY_JPEGIO = 0
+CIRCUITPY_ERRNO = 0
+CIRCUITPY_RAINBOWIO = 0
diff --git a/ports/atmel-samd/boards/feather_m0_express/mpconfigboard.mk b/ports/atmel-samd/boards/feather_m0_express/mpconfigboard.mk
index 783e2cb565783..1152fb4acc419 100644
--- a/ports/atmel-samd/boards/feather_m0_express/mpconfigboard.mk
+++ b/ports/atmel-samd/boards/feather_m0_express/mpconfigboard.mk
@@ -11,4 +11,5 @@ EXTERNAL_FLASH_DEVICES = "S25FL216K, GD25Q16C, W25Q16JVxQ"
 LONGINT_IMPL = MPZ
 
 CIRCUITPY_CODEOP = 0
+CIRCUITPY_ERRNO = 0
 CIRCUITPY_RAINBOWIO = 0
diff --git a/ports/atmel-samd/boards/feather_m0_supersized/mpconfigboard.mk b/ports/atmel-samd/boards/feather_m0_supersized/mpconfigboard.mk
index bd068adc943e2..dd58e8d1ce5a7 100644
--- a/ports/atmel-samd/boards/feather_m0_supersized/mpconfigboard.mk
+++ b/ports/atmel-samd/boards/feather_m0_supersized/mpconfigboard.mk
@@ -11,4 +11,5 @@ EXTERNAL_FLASH_DEVICES = "S25FL064L"
 LONGINT_IMPL = MPZ
 
 CIRCUITPY_CODEOP = 0
+CIRCUITPY_ERRNO = 0
 CIRCUITPY_RAINBOWIO = 0
diff --git a/ports/atmel-samd/boards/feather_m4_can/mpconfigboard.mk b/ports/atmel-samd/boards/feather_m4_can/mpconfigboard.mk
index a7c18acba3c55..ee414b6e214b0 100644
--- a/ports/atmel-samd/boards/feather_m4_can/mpconfigboard.mk
+++ b/ports/atmel-samd/boards/feather_m4_can/mpconfigboard.mk
@@ -17,6 +17,7 @@ CIRCUITPY_FLOPPYIO = 0
 CIRCUITPY_GIFIO = 0
 CIRCUITPY_I2CTARGET = 0
 CIRCUITPY_JPEGIO = 0
+CIRCUITPY_PS2IO = 0
 CIRCUITPY_SYNTHIO = 0
 
 CIRCUITPY_LTO_PARTITION = one
diff --git a/py/circuitpy_mpconfig.h b/py/circuitpy_mpconfig.h
index 27d4e97ad4d45..2754d57b01c9b 100644
--- a/py/circuitpy_mpconfig.h
+++ b/py/circuitpy_mpconfig.h
@@ -345,6 +345,9 @@ typedef long mp_off_t;
 #endif
 
 
+// For easy debugging printf's.
+#define PLAT_PRINTF(...) mp_printf(&mp_plat_print, __VA_ARGS__)
+
 #if MICROPY_PY_ASYNC_AWAIT && !CIRCUITPY_TRACEBACK
 #error CIRCUITPY_ASYNCIO requires CIRCUITPY_TRACEBACK
 #endif
diff --git a/shared-bindings/storage/__init__.c b/shared-bindings/storage/__init__.c
index ee0fb4ab53c3a..14ec16f3096c7 100644
--- a/shared-bindings/storage/__init__.c
+++ b/shared-bindings/storage/__init__.c
@@ -54,15 +54,11 @@ static mp_obj_t storage_mount(size_t n_args, const mp_obj_t *pos_args, mp_map_t
     // get the mount point
     const char *mnt_str = mp_obj_str_get_str(args[ARG_mount_path].u_obj);
 
-    // Make sure we're given an object we can mount.
-    // TODO(tannewt): Make sure we have all the methods we need to operating it
-    // as a file system.
+
     mp_obj_t vfs_obj = args[ARG_filesystem].u_obj;
-    mp_obj_t dest[2];
-    mp_load_method_maybe(vfs_obj, MP_QSTR_mount, dest);
-    if (dest[0] == MP_OBJ_NULL) {
-        mp_raise_ValueError(MP_ERROR_TEXT("filesystem must provide mount method"));
-    }
+
+    // Currently, the only supported filesystem is VfsFat.
+    mp_arg_validate_type(vfs_obj, &mp_fat_vfs_type, MP_QSTR_filesystem);
 
     common_hal_storage_mount(vfs_obj, mnt_str, args[ARG_readonly].u_bool);
 
diff --git a/shared-module/storage/__init__.c b/shared-module/storage/__init__.c
index 9a2c8271222e0..dedcee1ff23f5 100644
--- a/shared-module/storage/__init__.c
+++ b/shared-module/storage/__init__.c
@@ -126,6 +126,11 @@ void common_hal_storage_mount(mp_obj_t vfs_obj, const char *mount_path, bool rea
     // call the underlying object to do any mounting operation
     mp_vfs_proxy_call(vfs, MP_QSTR_mount, 2, (mp_obj_t *)&args);
 
+    fs_user_mount_t *vfs_fat = MP_OBJ_TO_PTR(vfs_obj);
+    // Filesystem is read-only to USB if writable by CircuitPython, and vice versa.
+    filesystem_set_writable_by_usb(vfs_fat, readonly);
+    filesystem_set_concurrent_write_protection(vfs_fat, true);
+
     // Insert the vfs into the mount table by pushing it onto the front of the
     // mount table.
     mp_vfs_mount_t **vfsp = &MP_STATE_VM(vfs_mount_table);
diff --git a/supervisor/shared/filesystem.c b/supervisor/shared/filesystem.c
index df70d963de6f1..24c7f9bffc552 100644
--- a/supervisor/shared/filesystem.c
+++ b/supervisor/shared/filesystem.c
@@ -247,13 +247,13 @@ void filesystem_set_writable_by_usb(fs_user_mount_t *vfs, bool usb_writable) {
 }
 
 bool filesystem_is_writable_by_python(fs_user_mount_t *vfs) {
-    return (vfs->blockdev.flags & MP_BLOCKDEV_FLAG_CONCURRENT_WRITE_PROTECTED) == 0 ||
-           (vfs->blockdev.flags & MP_BLOCKDEV_FLAG_USB_WRITABLE) == 0;
+    return ((vfs->blockdev.flags & MP_BLOCKDEV_FLAG_CONCURRENT_WRITE_PROTECTED) == 0) ||
+           ((vfs->blockdev.flags & MP_BLOCKDEV_FLAG_USB_WRITABLE) == 0);
 }
 
 bool filesystem_is_writable_by_usb(fs_user_mount_t *vfs) {
-    return (vfs->blockdev.flags & MP_BLOCKDEV_FLAG_CONCURRENT_WRITE_PROTECTED) == 0 ||
-           (vfs->blockdev.flags & MP_BLOCKDEV_FLAG_USB_WRITABLE) != 0;
+    return ((vfs->blockdev.flags & MP_BLOCKDEV_FLAG_CONCURRENT_WRITE_PROTECTED) == 0) ||
+           ((vfs->blockdev.flags & MP_BLOCKDEV_FLAG_USB_WRITABLE) != 0);
 }
 
 void filesystem_set_internal_concurrent_write_protection(bool concurrent_write_protection) {