lvgl/docs/overview/file-system.md

```eval_rst
.. include:: /header.rst 
:github_url: |github_link_base|/overview/file-system.md
```
# File system

LVGL has a 'File system' abstraction module that enables you to attach any type of file systems.
The file system is identified by a drive letter.
For example, if the SD card is associated with the letter `'S'`, a file can be reached like `"S:path/to/file.txt"`.

## Add a driver

To add a driver, `lv_fs_drv_t` needs to be initialized like this:
```c
lv_fs_drv_t drv;
lv_fs_drv_init(&drv);                     /*Basic initialization*/

drv.letter = 'S';                         /*An uppercase letter to identify the drive */
drv.file_size = sizeof(my_file_object);   /*Size required to store a file object*/
drv.rddir_size = sizeof(my_dir_object);   /*Size required to store a directory object (used by dir_open/close/read)*/
drv.ready_cb = my_ready_cb;               /*Callback to tell if the drive is ready to use */
drv.open_cb = my_open_cb;                 /*Callback to open a file */
drv.close_cb = my_close_cb;               /*Callback to close a file */
drv.read_cb = my_read_cb;                 /*Callback to read a file */
drv.write_cb = my_write_cb;               /*Callback to write a file */
drv.seek_cb = my_seek_cb;                 /*Callback to seek in a file (Move cursor) */
drv.tell_cb = my_tell_cb;                 /*Callback to tell the cursor position  */
drv.trunc_cb = my_trunc_cb;               /*Callback to delete a file */
drv.size_cb = my_size_cb;                 /*Callback to tell a file's size */
drv.rename_cb = my_rename_cb;             /*Callback to rename a file */


drv.dir_open_cb = my_dir_open_cb;         /*Callback to open directory to read its content */
drv.dir_read_cb = my_dir_read_cb;         /*Callback to read a directory's content */
drv.dir_close_cb = my_dir_close_cb;       /*Callback to close a directory */

drv.free_space_cb = my_free_space_cb;     /*Callback to tell free space on the drive */

drv.user_data = my_user_data;             /*Any custom data if required*/

lv_fs_drv_register(&drv);                 /*Finally register the drive*/

```

Any of the callbacks can be `NULL` to indicate that operation is not supported.

As an example of how the callbacks are used, if you use `lv_fs_open(&file, "S:/folder/file.txt", LV_FS_MODE_WR)`, LVGL:

1. Verifies that a registered drive exists with the letter `'S'`.
2. Checks if it's `open_cb` is implemented (not `NULL`).
3. Calls the set `open_cb` with `"folder/file.txt"` path.

## Usage example

The example below shows how to read from a file:
```c
lv_fs_file_t f;
lv_fs_res_t res;
res = lv_fs_open(&f, "S:folder/file.txt", LV_FS_MODE_RD);
if(res != LV_FS_RES_OK) my_error_handling();

uint32_t read_num;
uint8_t buf[8];
res = lv_fs_read(&f, buf, 8, &read_num);
if(res != LV_FS_RES_OK || read_num != 8) my_error_handling();

lv_fs_close(&f);
```
*The mode in `lv_fs_open` can be `LV_FS_MODE_WR` to open for write or `LV_FS_MODE_RD | LV_FS_MODE_WR` for both*

This example shows how to read a directory's content. It's up to the driver how to mark the directories, but it can be a good practice to insert a `'/'` in front of the directory name.
```c
lv_fs_dir_t dir;
lv_fs_res_t res;
res = lv_fs_dir_open(&dir, "S:/folder");
if(res != LV_FS_RES_OK) my_error_handling();

char fn[256];
while(1) {
    res = lv_fs_dir_read(&dir, fn);
    if(res != LV_FS_RES_OK) {
        my_error_handling();
        break;
    }

    /*fn is empty, if not more files to read*/
    if(strlen(fn) == 0) {
        break;
    }

    printf("%s\n", fn);
}

lv_fs_dir_close(&dir);
```

## Use drivers for images

[Image](/widgets/core/img) objects can be opened from files too (besides variables stored in the flash).

To initialize the image, the following callbacks are required:
- open
- close
- read
- seek
- tell


## API

```eval_rst

.. doxygenfile:: lv_fs.h
  :project: lvgl

```