180 lines
3.7 KiB
C
180 lines
3.7 KiB
C
#include <assert.h>
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#include <fat32.h>
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#include <mmu.h>
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#include <string.h>
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#include <x86.h>
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#include <kern/keyboard.h>
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#include <kern/fs.h>
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#include <kern/stdio.h>
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#include <kern/syscall.h>
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/*
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* 内核读入函数，由于没有文件描述符概念，
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* 所以强制assert让fd为0，平时的读入流也默认是0的
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* 现在只有从键盘缓冲区获取字符的能力
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*/
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ssize_t
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kern_read(int fd, void *buf, size_t count)
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{
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assert(fd == 0);
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char *s = buf;
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for (size_t i = 0 ; i < count ; i++) {
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char c = read_keyboard_buf();
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if (c == -1)
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return i;
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*s++ = c;
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}
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return count;
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}
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ssize_t
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do_read(int fd, void *buf, size_t count)
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{
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assert(buf < (void *)KERNBASE);
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assert(buf + count < (void *)KERNBASE);
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return kern_read(fd, buf, count);
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}
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/*
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* 内核写入函数，由于没有文件描述符概念，
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* 所以强制assert让fd为1，平时的输出流也默认是1的
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* 现在只有输出字符到终端的能力
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*/
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ssize_t
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kern_write(int fd, const void *buf, size_t count)
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{
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assert(fd == 1);
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const char *s = buf;
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for (size_t i = 0 ; i < count ; i++)
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kprintf("%c", *s++);
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return count;
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}
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ssize_t
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do_write(int fd, const void *buf, size_t count)
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{
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assert(buf < (void *)KERNBASE);
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assert(buf + count < (void *)KERNBASE);
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return kern_write(fd, buf, count);
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}
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#define SECTSIZE 512
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static void
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waitdisk(void)
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{
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// wait for disk reaady
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while ((inb(0x1F7) & 0xC0) != 0x40)
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/* do nothing */;
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}
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static void
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readsect(void *dst, u32 offset)
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{
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// wait for disk to be ready
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waitdisk();
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outb(0x1F2, 1); // count = 1
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outb(0x1F3, offset);
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outb(0x1F4, offset >> 8);
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outb(0x1F5, offset >> 16);
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outb(0x1F6, (offset >> 24) | 0xE0);
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outb(0x1F7, 0x20); // cmd 0x20 - read sectors
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// wait for disk to be ready
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waitdisk();
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// read a sector
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insl(0x1F0, dst, SECTSIZE/4);
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}
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u32 fat_start_sec;
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u32 data_start_sec;
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u32 fat_now_sec;
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struct BPB bpb;
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/*
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* 获取下一个簇号
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*/
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static u32
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get_next_clus(u32 current_clus)
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{
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u32 sec = current_clus * 4 / SECTSIZE;
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u32 off = current_clus * 4 % SECTSIZE;
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static u32 buf[SECTSIZE / 4];
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if (fat_now_sec != fat_start_sec + sec) {
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readsect(buf, fat_start_sec + sec);
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fat_now_sec = fat_start_sec + sec;
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}
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return buf[off / 4];
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}
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/*
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* 读入簇号对应的数据区的所有数据
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* 读到dst开头的位置，返回读入的尾指针
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*/
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static void *
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read_data_sec(void *dst, u32 current_clus)
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{
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current_clus -= 2;
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current_clus *= bpb.BPB_SecPerClus;
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current_clus += data_start_sec;
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for (int i = 0 ; i < bpb.BPB_SecPerClus ; i++, dst += SECTSIZE)
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readsect(dst, current_clus + i);
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return dst;
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}
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/*
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* 根据filename读取文件到dst处
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* filename要求是短目录项名（11个字节）
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* dst推荐是3GB + 48MB
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*/
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void
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read_file(const char *filename, void *dst)
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{
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assert(strlen(filename) == 11);
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readsect(&bpb, 0);
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fat_start_sec = bpb.BPB_RsvdSecCnt;
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data_start_sec = fat_start_sec + bpb.BPB_FATSz32 * bpb.BPB_NumFATs;
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u32 root_clus = bpb.BPB_RootClus;
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u32 file_clus = 0;
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assert(bpb.BPB_BytsPerSec == SECTSIZE && bpb.BPB_SecPerClus == 8);
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static char buf[SECTSIZE * 8];
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// 遍历目录项获取文件起始簇号
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while (root_clus < 0x0FFFFFF8) {
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void *read_end = read_data_sec((void *)buf, root_clus);
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for (struct Directory_Entry *p = (void *)buf
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; (void *)p < read_end ; p++) {
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if (strncmp(p->DIR_Name, filename, 11) == 0) {
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assert(p->DIR_FileSize <= 16 * MB);
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file_clus = (u32)p->DIR_FstClusHI << 16 |
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p->DIR_FstClusLO;
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break;
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}
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}
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if (file_clus != 0)
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break;
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root_clus = get_next_clus(root_clus);
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}
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if (file_clus == 0)
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panic("file can't found! filename: %s", filename);
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// 读入文件
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while (file_clus < 0x0FFFFFF8) {
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dst = read_data_sec(dst, file_clus);
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file_clus = get_next_clus(file_clus);
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}
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} |