Change vfs mount ordering such that the root is always last in the

linked list. Its also the only one statically allocated and made
available over USB.

atmel-samd/access_vfs.c

@@ -42,15 +42,13 @@
 
 #define VFS_INDEX 0
 
+// The root FS is always at the end of the list.
 static fs_user_mount_t* get_vfs(int index) {
     mp_vfs_mount_t* current_mount = MP_STATE_VM(vfs_mount_table);
-    for (uint8_t i = 0; current_mount != NULL; i++) {
-        if (i == VFS_INDEX) {
-            return (fs_user_mount_t *) current_mount->obj;
-        }
+    while (current_mount->next != NULL) {
         current_mount = current_mount->next;
     }
-    return NULL;
+    return current_mount->obj;
 }
 
 //! This function tests memory state, and starts memory initialization

py/runtime.c

@@ -117,18 +117,22 @@ void mp_init(void) {
 
     #if MICROPY_VFS
     #if MICROPY_FATFS_NUM_PERSISTENT > 0
+    // We preserve the last MICROPY_FATFS_NUM_PERSISTENT mounts because newer
+    // mounts are put at the front of the list.
     mp_vfs_mount_t *vfs = MP_STATE_VM(vfs_mount_table);
-    if (vfs != NULL) {
-        MP_STATE_VM(vfs_cur) = vfs;
+    // Count how many mounts we have.
+    uint8_t count = 0;
+    while (vfs != NULL) {
+        vfs = vfs->next;
+        count++;
     }
-    // Skip forward until the vfs->next pointer is the first vfs that shouldn't
-    // persist.
-    uint8_t i = 1;
-    while (vfs != NULL && i < MICROPY_FATFS_NUM_PERSISTENT) {
+    // Find the vfs MICROPY_FATFS_NUM_PERSISTENT mounts from the end.
+    vfs = MP_STATE_VM(vfs_mount_table);
+    for (uint8_t j = 0; j < count - MICROPY_FATFS_NUM_PERSISTENT; j++) {
         vfs = vfs->next;
-        i++;
     }
-    vfs->next = NULL;
+    MP_STATE_VM(vfs_mount_table) = vfs;
+    MP_STATE_VM(vfs_cur) = vfs;
     #else
     // initialise the VFS sub-system
     MP_STATE_VM(vfs_cur) = NULL;

shared-module/storage/__init__.c

@@ -78,16 +78,10 @@ void common_hal_storage_mount(mp_obj_t vfs_obj, const char* mount_path, bool rea
         }
     }
 
-    // insert the vfs into the mount table
+    // 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);
-    while (*vfsp != NULL) {
-        if ((*vfsp)->len == 1) {
-            // make sure anything mounted at the root stays at the end of the list
-            vfs->next = *vfsp;
-            break;
-        }
-        vfsp = &(*vfsp)->next;
-    }
+    vfs->next = *vfsp;
     *vfsp = vfs;
 }