178 lines
5.9 KiB
Markdown
178 lines
5.9 KiB
Markdown
# LLFS (Linked List File System)
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## Introduction
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The llfs filesystem can be generated using the [mkllfs](mkllfs.md) utility.
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The resulting C file encapsulates the filesystem data within a linked list which can be used by the llfs library.
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As a flat filesystem, llfs lacks support for directories.
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Using the llfs API, information about the files in the filesystem can be retrieved,
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and the files can be read using direct memory access.
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Alternatively, the POSIX file functions can be used.
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But this is more resource intensive, as data must be copied before using it.
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It's essential to note that the llfs filesystem operates in a read-only mode,
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restricting operations solely to read functions.
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## Table of contents
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- [Introduction](#introduction)
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- [Table of contents](#table-of-contents)
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- [Initialization](#initialization)
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- [Usage of the llfs API](#usage-of-the-llfs-api)
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- [The `llfs_file_t` struct](#the-llfs_file_t-struct)
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- [Getting a list of files](#getting-a-list-of-files)
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- [Iterator function (not recommended)](#iterator-function-not-recommended)
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- [Reading a file](#reading-a-file)
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- [Getting the number of files](#getting-the-number-of-files)
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- [Using the POSIX file functions](#using-the-posix-file-functions)
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- [Enabling the external loader in STM32CubeIDE](#enabling-the-external-loader-in-stm32cubeide)
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## Initialization
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Before using the llfs API, or the file related POSIX (fopen, fgetc, ...) functions, the filesystem must be initialized by calling `llfs_init()`.
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## Usage of the llfs API
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### The `llfs_file_t` struct
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The `llfs_file_t` struct contains information about a file in the filesystem.
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```c
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typedef struct {
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const uint8_t* data; // Pointer to the file data (len bytes)
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const char* name; // Null-terminated string with the filename
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size_t len; // Length of the file data
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} llfs_file_t;
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```
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The data pointer points to the data of the file in the filesystem, and can be used to read the file.
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### Getting a list of files
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```c
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#include "llfs.h"
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void main(void) {
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llfs_init();
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// Allocate space for 10 files
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llfs_file_t file_list[10];
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// Get the file list
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size_t file_count = llfs_file_list(file_list, 10, NULL);
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// Loop through the files and print their names and sizes
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for (int i = 0; i < file_count; i++) {
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LOG_INFO(TAG, "File: %s, size: %d", file_list[i].name, file_list[i].len);
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}
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}
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```
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Result:
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```
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[Info] (2009) [main]: File: image.bmp, size: 9270
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[Info] (2013) [main]: File: python_file.py, size: 645
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[Info] (2019) [main]: File: image2.bmp, size: 7738
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[Info] (2024) [main]: File: filename with a space.txt, size: 61
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[Info] (2031) [main]: File: file1.txt, size: 77
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```
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It is also possible to use a file extension filter (e.g. `*.bmp`, `*.txt`, `*.py`).
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```c
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// ...
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size_t file_count = llfs_file_list(file_list, 10, "*.bmp");
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// ...
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```
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This will only return files with the `.bmp` extension.
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````
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[Info] (2009) [main]: File: image.bmp, size: 9270
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[Info] (2019) [main]: File: image2.bmp, size: 7738
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````
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#### Iterator function (not recommended)
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It is also possible to iterate through the files without allocating an array.
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When the memory pointer is `NULL`, the iterator will start at the beginning of the file list.
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Each call to `llfs_next_file()` will return the next file in the list,
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if a filter is specified files that don't match the filter will be skipped.
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```c
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#include "llfs.h"
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void main(void) {
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llfs_init();
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// Get the file list
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void* mem = NULL; // Pointer for internal use by the llfs library
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llfs_file_t* file;
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while ((file = llfs_next_file(&mem, ".bmp")) != NULL) {
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LOG_INFO(TAG, "File: %s", file->name);
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}
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}
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```
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While this method doesn't require allocating memory for the file list,
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it is slower than the previous method due to the overhead calling the function for each file.
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Additionally, the required memory for the filelist is very small, so it's recommended to use the first method.
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### Reading a file
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```c
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#include "llfs.h"
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void main(void) {
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llfs_init();
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// Get a file by name
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llfs_file_t* file = llfs_file_open("filename with a space.txt");
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if (file != NULL) {
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// Print the file name, size and data
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LOG_INFO(TAG, "File found: %s, size: %d", file->name, file->len);
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LOG_INFO(TAG, "File data: %s", file->data);
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} else {
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LOG_WARN(TAG, "File not found");
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}
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}
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```
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Result:
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```
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[Info] (2040) [main]: File found: filename with a space.txt, size: 61
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[Info] (2047) [main]: File data: This is a file with a space in it's filename.
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```
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### Getting the number of files
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```c
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#include "llfs.h"
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void main(void) {
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llfs_init();
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// Get the number of files
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size_t file_count = llfs_file_count();
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// Print the number of files
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LOG_INFO(TAG, "File count: %d", file_count);
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}
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```
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## Using the POSIX file functions
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The llfs library also supports the POSIX file functions.
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As the file system is read-only, write functions are not implemented.
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There is also a limit on the number of files that can be open concurrently,
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this is set by the `POSIX_MAX_FILES` macro in `llfs.c`.
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The default value is 10, but there are already 3 files in use (stdin, stdout, stderr),
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so the maximum number of files that can be open is 7.
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The following functions are tested and working, but other functions might also work:
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- `fopen`
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- `fclose`
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- `fgetc`
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- `fread`
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- `fseek`
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- `ftell`
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- `rewind`
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- `fstat`
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- `fileno`
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## Enabling the external loader in STM32CubeIDE
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In order to write the file system data to the QSPI flash, the external loader must be enabled in STM32CubeIDE.
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This can be done by opening the debug configuration:
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Then, in the `Debugger` tab:
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3. Enable the `External Loader`
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4. Click the `Scan` button
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5. Select the correct loader: `N25Q128A_STM32F746G-DISCO, 0x90000000 ...`
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