用c语言为 LINUX 设计一个简单的二级文件系统

以下是一个简单的二级文件系统的 C 语言实现示例：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

#define BLOCK_SIZE 1024
#define MAX_BLOCKS 1024
#define MAX_FILES 128
#define MAX_FILENAME_LENGTH 32
#define MAX_PATH_LENGTH 256

typedef struct {
    int block_num;
    time_t created_at;
    time_t modified_at;
    int size;
} FileControlBlock;

typedef struct {
    char name[MAX_FILENAME_LENGTH];
    int parent_dir;
    int is_file;
    int fcb_index;
} DirectoryEntry;

typedef struct {
    char data[BLOCK_SIZE];
    int next_block;
} DataBlock;

int free_blocks[MAX_BLOCKS]; // 空闲块列表
int free_blocks_count = 0; // 空闲块数量
FileControlBlock fcb_table[MAX_FILES]; // FCB 表
DirectoryEntry directory[MAX_FILES]; // 目录表
int directory_count = 0; // 目录项数量
DataBlock data_blocks[MAX_BLOCKS]; // 数据块
int data_block_count = 0; // 数据块数量

int allocate_block() {
    if (free_blocks_count == 0) {
        return -1;
    }
    int block_index = free_blocks[free_blocks_count - 1];
    free_blocks_count--;
    return block_index;
}

void free_block(int block_index) {
    free_blocks[free_blocks_count] = block_index;
    free_blocks_count++;
}

void write_block(int block_index, void* data) {
    memcpy(data_blocks[block_index].data, data, BLOCK_SIZE);
    fcb_table[block_index].modified_at = time(NULL);
}

void read_block(int block_index, void* data) {
    memcpy(data, data_blocks[block_index].data, BLOCK_SIZE);
}

int create_file(char* name, int parent_dir) {
    if (directory_count >= MAX_FILES || strlen(name) > MAX_FILENAME_LENGTH) {
        return -1;
    }
    int fcb_index = allocate_block();
    if (fcb_index == -1) {
        return -1;
    }
    fcb_table[fcb_index].block_num = 1;
    fcb_table[fcb_index].created_at = time(NULL);
    fcb_table[fcb_index].modified_at = time(NULL);
    fcb_table[fcb_index].size = 0;
    int dir_index = directory_count;
    directory[dir_index].parent_dir = parent_dir;
    directory[dir_index].is_file = 1;
    directory[dir_index].fcb_index = fcb_index;
    strcpy(directory[dir_index].name, name);
    directory_count++;
    return dir_index;
}

int create_directory(char* name, int parent_dir) {
    int dir_index = create_file(name, parent_dir);
    if (dir_index == -1) {
        return -1;
    }
    fcb_table[dir_index].block_num = 0;
    return dir_index;
}

void delete_file(int index) {
    for (int i = 0; i < directory_count; i++) {
        if (directory[i].parent_dir == index) {
            delete_file(i);
        }
    }
    free_block(directory[index].fcb_index);
    for (int i = index; i < directory_count - 1; i++) {
        directory[i] = directory[i + 1];
    }
    directory_count--;
}

int get_directory(char* path) {
    int dir_index = 0; // 从根目录开始
    char* name = strtok(path, "/");
    while (name != NULL) {
        int found = 0;
        for (int i = 0; i < directory_count; i++) {
            if (directory[i].parent_dir == dir_index && strcmp(directory[i].name, name) == 0) {
                found = 1;
                dir_index = i;
                break;
            }
        }
        if (!found) {
            return -1;
        }
        name = strtok(NULL, "/");
    }
    return dir_index;
}

void print_directory(int index, char* prefix) {
    for (int i = 0; i < directory_count; i++) {
        if (directory[i].parent_dir == index) {
            printf("%s%s\n", prefix, directory[i].name);
            if (!directory[i].is_file) {
                char new_prefix[MAX_PATH_LENGTH];
                sprintf(new_prefix, "%s  ", prefix);
                print_directory(i, new_prefix);
            }
        }
    }
}

int main() {
    // 初始化空闲块列表
    for (int i = 0; i < MAX_BLOCKS; i++) {
        free_blocks[i] = i;
    }
    free_blocks_count = MAX_BLOCKS;
    // 创建根目录
    create_directory("/", -1);
    // 测试创建文件和目录
    int dir1_index = create_directory("dir1", 0);
    int file1_index = create_file("file1.txt", 0);
    int dir2_index = create_directory("dir2", dir1_index);
    int file2_index = create_file("file2.txt", dir1_index);
    // 测试删除文件和目录
    delete_file(file2_index);
    delete_file(dir1_index);
    // 测试查找目录
    int dir_index = get_directory("/dir1/dir2");
    if (dir_index != -1) {
        printf("Found directory /dir1/dir2\n");
    }
    // 测试打印目录
    print_directory(0, "");
    return 0;
}

以上是一个简单的二级文件系统的 C 语言实现示例，它包含了文件控制块、目录、存储空间管理器等基本组件，可以实现创建、删除、查找、打印目录，创建、删除文件和目录等基本操作。实际的文件系统可能需要更多的功能和优化，例如权限管理、文件压缩、文件加密等等。