extmod/vfs_rom: Add VfsRom filesystem object.

This commit defines a new ROMFS filesystem for storing read-only files that
can be memory mapped, and a new VfsRom driver.  Files opened from this
filesystem support the buffer protocol.  This allows naturally getting the
memory-mapped address of the file using:
- memoryview(file)
- uctypes.addressof(file)

Furthermore, if these files are .mpy files then their content can be
referenced in-place when importing.  Such imports take up a lot less RAM
than importing from a normal filesystem.  This is essentially dynamically
frozen .mpy files, building on the revamped v6 .mpy file format.

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

1 files changed, 47 insertions, 0 deletions

diff --git a/extmod/vfs_rom.h b/extmod/vfs_rom.h
new file mode 100644
index 000000000..d8e2b911b
--- /dev/null
+++ b/extmod/vfs_rom.h
@@ -0,0 +1,47 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2022 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+#ifndef MICROPY_INCLUDED_EXTMOD_VFS_ROM_H
+#define MICROPY_INCLUDED_EXTMOD_VFS_ROM_H
+
+#include "py/builtin.h"
+#include "py/obj.h"
+
+#if MICROPY_VFS_ROM
+
+typedef struct _mp_obj_vfs_rom_t mp_obj_vfs_rom_t;
+
+extern const mp_obj_type_t mp_type_vfs_rom;
+
+static inline const char *mp_vfs_rom_get_path_str(mp_obj_vfs_rom_t *self, mp_obj_t path) {
+    return mp_obj_str_get_str(path);
+}
+
+mp_import_stat_t mp_vfs_rom_search_filesystem(mp_obj_vfs_rom_t *self, const char *path, size_t *size_out, const uint8_t **data_out);
+mp_obj_t mp_vfs_rom_file_open(mp_obj_t self_in, mp_obj_t path_in, mp_obj_t mode_in);
+
+#endif // MICROPY_VFS_ROM
+
+#endif // MICROPY_INCLUDED_EXTMOD_VFS_ROM_H