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mkfs: first working version

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It can create a basic filesystem of arbitrary size.

Signed-off-by: Sean Cross <sean@xobs.io>
This commit is contained in:
Sean Cross
2019-06-09 15:48:07 +08:00
parent ab97abe22a
commit f68f8215b7
5 changed files with 141 additions and 46 deletions
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11
src/fat12.c
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@@ -1,5 +1,16 @@
#include "fat12.h"
void fat12_write_u8(void *ptr, uint8_t val) {
((uint8_t *)ptr)[0] = (val >> 0) & 0xff;
}
uint8_t fat12_read_u8(void *ptr) {
uint16_t val = 0;
val |= (((uint8_t *)ptr)[0] << 0) & 0xff;
return val;
}
void fat12_write_u16(void *ptr, uint16_t val) {
((uint8_t *)ptr)[0] = (val >> 0) & 0xff;
((uint8_t *)ptr)[1] = (val >> 8) & 0xff;

112
src/mkfat.c
View File

@@ -2,31 +2,40 @@
#include <unistd.h>
#include <string.h>
#include "fat12.h"
#include "io.h"
struct directory_entry {
uint8_t file_name[8];
uint8_t extension[3];
uint8_t file_attributes;
uint8_t reserved1;
uint8_t ctime_ms;
uint8_t ctime_hms[2];
uint8_t ctime_date[2];
uint8_t atime_date[2];
uint8_t ea_index[2];
uint8_t mtime_hms[2];
uint8_t mtime_date[2];
uint8_t first_cluster[2];
uint8_t file_size[4];
};
// Create a FAT12 filesystem using the given file descriptor,
// with length _bytes_.
// It will define a root directory size and padding size so that the file sectors
// end up on 4096-byte boundaries.
int fat12_mkfs(int fd, uint32_t bytes) {
uint8_t mbr[512];
const uint16_t sector_size = 512;
const uint8_t cluster_size = 8; // 4 kiB cluster sizes match flash erase block size
const uint32_t sector_size = 512;
uint32_t cluster_size = 4096 / sector_size; // 4 kiB cluster sizes match flash erase block size
if (bytes > 16000) {
// We run out of clusters just below 16 megabytes. Use bigger cluseters.
cluster_size = 8192 / sector_size;
}
const uint32_t reserved_sectors = 1; // The MBR is the only reserved sector
// XXX What happens if this is an even multiple of sectors?
// Size of FAT (in bytes)
uint32_t fat_size = 1 + ((((bytes * 3) / sector_size) / cluster_size) / 2);
uint32_t fat_size_sectors = ((fat_size - 1) / sector_size) + 1;
uint32_t root_directory_sector_count = cluster_size - (fat_size_sectors + reserved_sectors);
uint32_t root_directory_entry_count = (sector_size / sizeof(struct fat_directory_entry)) * root_directory_sector_count;
// fprintf(stderr, "bytes: %d\n", bytes);
// fprintf(stderr, "sector_size: %d\n", sector_size);
// fprintf(stderr, "cluster_size: %d\n", cluster_size);
// fprintf(stderr, "reserved_sectors: %d\n", reserved_sectors);
// fprintf(stderr, "fat_size: %d\n", fat_size);
// fprintf(stderr, "fat_size_sectors: %d\n", fat_size_sectors);
// fprintf(stderr, "root_directory_sector_count: %d\n", root_directory_sector_count);
// fprintf(stderr, "root_directory_entry_count: %d\n", root_directory_entry_count);
// fprintf(stderr, "\n");
memset(mbr, 0, sizeof(mbr));
@@ -42,25 +51,25 @@ int fat12_mkfs(int fd, uint32_t bytes) {
fat12_write_u16(mbr + 0x0b, sector_size);
// Sectors per cluster (8), so cluster is 512 * 8
mbr[0x0d] = cluster_size;
fat12_write_u8(mbr + 0x0d, cluster_size);
// Reserved sector count (8 sectors, to pad things to 4096-byte boundaries)
fat12_write_u16(mbr + 0x0e, cluster_size);
fat12_write_u16(mbr + 0x0e, reserved_sectors);
// Number of FATs (1)
mbr[0x10] = 1;
fat12_write_u8(mbr + 0x10, 1);
// Maximum number of root directory entries (16)
fat12_write_u16(mbr + 0x11, 32);
fat12_write_u16(mbr + 0x11, root_directory_entry_count);
// Total number of 512-byte sectors
fat12_write_u16(mbr + 0x13, bytes / sector_size);
// Type of media (0xf8 == fixed disk)
mbr[0x15] = 0xf8;
fat12_write_u8(mbr + 0x15, 0xf8);
// Sectors per FAT
fat12_write_u16(mbr + 0x16, fat_size);
fat12_write_u16(mbr + 0x16, fat_size_sectors);
// Sectors per track
fat12_write_u16(mbr + 0x18, 32);
@@ -69,31 +78,31 @@ int fat12_mkfs(int fd, uint32_t bytes) {
fat12_write_u16(mbr + 0x1a, 64);
// Hidden sectors
mbr[0x1c] = 0x00;
mbr[0x1d] = 0x00;
mbr[0x1e] = 0x00;
mbr[0x1f] = 0x00;
// mbr[0x1c] = 0x00;
// mbr[0x1d] = 0x00;
// mbr[0x1e] = 0x00;
// mbr[0x1f] = 0x00;
// Total number of sectors (unused, since we put it in 0x13)
mbr[0x20] = 0;
mbr[0x21] = 0;
mbr[0x22] = 0;
mbr[0x23] = 0;
// mbr[0x20] = 0;
// mbr[0x21] = 0;
// mbr[0x22] = 0;
// mbr[0x23] = 0;
// BIOS drive
mbr[0x24] = 0x80;
fat12_write_u8(mbr + 0x24, 0x80);
// Unused
mbr[0x25] = 0;
fat12_write_u8(mbr + 0x25, 0);
// Boot signature
mbr[0x26] = 0x29;
fat12_write_u8(mbr + 0x26, 0x29);
// Serial number
mbr[0x27] = 0xf0;
mbr[0x28] = 0xb0;
mbr[0x29] = 0x00;
mbr[0x2a] = 0x07;
fat12_write_u8(mbr + 0x27, 0xf0);
fat12_write_u8(mbr + 0x28, 0xb0);
fat12_write_u8(mbr + 0x29, 0x00);
fat12_write_u8(mbr + 0x2a, 0x07);
// Volume Name
memcpy(mbr + 0x2b, "Fomu ", 11);
@@ -102,8 +111,8 @@ int fat12_mkfs(int fd, uint32_t bytes) {
memcpy(mbr + 0x36, "FAT12 ", 8);
// Signature
mbr[0xfe] = 0x55;
mbr[0xff] = 0xaa;
fat12_write_u8(mbr + 0xfe, 0x55);
fat12_write_u8(mbr + 0xff, 0xaa);
// Write MBR to disk
if (pang_write(fd, mbr, sizeof(mbr)) != sizeof(mbr)) {
@@ -112,16 +121,33 @@ int fat12_mkfs(int fd, uint32_t bytes) {
memset(mbr, 0, sizeof(mbr));
// The first two clusters in the FAT are reserved, and must be 0xff
// The first two clusters in the FAT are reserved
fat12_set_cluster(mbr, 0, 0xff8); // 0xff8 instead of 0xfff indicates "Hard Disk"
fat12_set_cluster(mbr, 1, 0xfff); // 0xfff is reserved value
// Root directory is only one cluster
fat12_set_cluster(mbr, 2, 0xfff);
// fat12_set_cluster(mbr, 2, 0xfff);
if (pang_write(fd, mbr, sizeof(mbr)) != sizeof(mbr)) {
return -1;
}
// Fill in the rest of the FAT
uint32_t fat_sector;
memset(mbr, 0, sizeof(mbr));
for (fat_sector = 1; fat_sector < fat_size_sectors; fat_sector++) {
if (pang_write(fd, mbr, sizeof(mbr)) != sizeof(mbr)) {
return -1;
}
}
// Fill in the root directory
uint32_t root_directory_sector;
for (root_directory_sector = 0; root_directory_sector < cluster_size; root_directory_sector++) {
if (pang_write(fd, mbr, sizeof(mbr)) != sizeof(mbr)) {
return -1;
}
}
return 0;
}