extmod/vfs_lfs: Support mounting LFS filesystems in read-only mode.

Signed-off-by: Damien George <damien@micropython.org>

extmod/vfs_lfsx.c

@@ -423,10 +423,16 @@ STATIC mp_obj_t MP_VFS_LFSx(statvfs)(mp_obj_t self_in, mp_obj_t path_in) {
 STATIC MP_DEFINE_CONST_FUN_OBJ_2(MP_VFS_LFSx(statvfs_obj), MP_VFS_LFSx(statvfs));
 
 STATIC mp_obj_t MP_VFS_LFSx(mount)(mp_obj_t self_in, mp_obj_t readonly, mp_obj_t mkfs) {
-    (void)self_in;
-    (void)readonly;
+    MP_OBJ_VFS_LFSx *self = MP_OBJ_TO_PTR(self_in);
     (void)mkfs;
-    // already called LFSx_API(mount) in MP_VFS_LFSx(make_new)
+
+    // Make block device read-only if requested.
+    if (mp_obj_is_true(readonly)) {
+        self->blockdev.writeblocks[0] = MP_OBJ_NULL;
+    }
+
+    // Already called LFSx_API(mount) in MP_VFS_LFSx(make_new) so the filesystem is ready.
+
     return mp_const_none;
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_3(MP_VFS_LFSx(mount_obj), MP_VFS_LFSx(mount));

tests/extmod/vfs_lfs_mount.py

@@ -67,6 +67,23 @@ def test(bdev, vfs_class):
     # umount
     uos.umount("/lfs")
 
+    # mount read-only
+    vfs = vfs_class(bdev)
+    uos.mount(vfs, "/lfs", readonly=True)
+
+    # test reading works
+    with open("/lfs/subdir/lfsmod2.py") as f:
+        print("lfsmod2.py:", f.read())
+
+    # test writing fails
+    try:
+        open("/lfs/test_write", "w")
+    except OSError as er:
+        print(repr(er))
+
+    # umount
+    uos.umount("/lfs")
+
     # clear imported modules
     usys.modules.clear()
 

tests/extmod/vfs_lfs_mount.py.exp

@@ -2,7 +2,13 @@ test <class 'VfsLfs1'>
 hello from lfs
 package
 hello from lfs
+lfsmod2.py: print("hello from lfs")
+
+OSError(30,)
 test <class 'VfsLfs2'>
 hello from lfs
 package
 hello from lfs
+lfsmod2.py: print("hello from lfs")
+
+OSError(36,)