ref: e81c54ba2ecc673a4d5f8aed0e9b52841fe07b0d
dir: /os/boot/pc/fat.c/
#include <u.h>
#include "fns.h"
#define GETSHORT(p) (*(ushort *)(p))
#define GETLONG(p) (*(uint *)(p))
enum {
Sectsz = 0x200,
Dirsz = 0x20,
Maxpath = 64,
Fat12 = 1,
Fat16 = 2,
Fat32 = 4,
};
typedef struct File File;
typedef struct Dir Dir;
typedef struct Pbs Pbs;
typedef struct Pbs32 Pbs32;
typedef struct Fat Fat;
struct Fat
{
ulong ver;
int drive;
ulong clustsize;
ulong eofmark;
ulong partlba;
ulong fatlba;
ulong dirstart; /* LBA for FAT16, cluster for FAT32 */
ulong dirents;
ulong datalba;
};
struct File
{
Fat *fat;
ulong lba;
ulong clust;
ulong lbaoff;
ulong len;
uchar *rp;
uchar *ep;
uchar buf[Sectsz];
};
struct Dir
{
char name[11];
uchar attr;
uchar reserved;
uchar ctime;
uchar ctime[2];
uchar cdate[2];
uchar adate[2];
uchar starthi[2];
uchar mtime[2];
uchar mdate[2];
uchar startlo[2];
uchar len[4];
};
struct Pbs
{
uchar magic[3];
uchar version[8];
uchar sectsize[2];
uchar clustsize;
uchar nreserv[2];
uchar nfats;
uchar rootsize[2];
uchar volsize[2];
uchar mediadesc;
uchar fatsize[2];
uchar trksize[2];
uchar nheads[2];
uchar nhidden[4];
uchar bigvolsize[4];
uchar driveno;
uchar reserved0;
uchar bootsig;
uchar volid[4];
uchar label[11];
uchar type[8];
};
struct Pbs32
{
uchar common[36];
uchar fatsize[4];
uchar flags[2];
uchar ver[2];
uchar rootclust[4];
uchar fsinfo[2];
uchar bootbak[2];
uchar reserved0[12];
uchar driveno;
uchar reserved1;
uchar bootsig;
uchar volid[4];
uchar label[11];
uchar type[8];
};
int readsect(ulong drive, ulong lba, void *buf);
void
unload(void)
{
}
static ulong
readnext(File *fp, ulong clust)
{
Fat *fat = fp->fat;
uchar tmp[2], *p;
ulong idx, lba;
if(fat->ver == Fat12)
idx = (3*clust)/2;
else
idx = clust*fat->ver;
lba = fat->fatlba + (idx / Sectsz);
if(readsect(fat->drive, lba, fp->buf))
memset(fp->buf, 0xff, Sectsz);
p = &fp->buf[idx % Sectsz];
if(p == &fp->buf[Sectsz-1]){
tmp[0] = *p;
if(readsect(fat->drive, ++lba, fp->buf))
memset(fp->buf, 0xff, Sectsz);
tmp[1] = fp->buf[0];
p = tmp;
}
if(fat->ver == Fat32)
return GETLONG(p) & 0xfffffff;
idx = GETSHORT(p);
if(fat->ver == Fat12){
if(clust & 1)
idx >>= 4;
idx &= 0xfff;
}
return idx;
}
int
read(void *f, void *data, int len)
{
File *fp = f;
Fat *fat = fp->fat;
if(fp->len > 0 && fp->rp >= fp->ep){
if(fp->clust != ~0U){
if(fp->lbaoff % fat->clustsize == 0){
if(fp->clust < 2 || fp->clust >= fat->eofmark)
return -1;
fp->lbaoff = (fp->clust - 2) * fat->clustsize;
fp->clust = readnext(fp, fp->clust);
fp->lba = fp->lbaoff + fat->datalba;
}
fp->lbaoff++;
}
if(readsect(fat->drive, fp->lba++, fp->rp = fp->buf))
return -1;
}
if(fp->len < len)
len = fp->len;
if(len > (fp->ep - fp->rp))
len = fp->ep - fp->rp;
memmove(data, fp->rp, len);
fp->rp += len;
fp->len -= len;
return len;
}
void
close(void *)
{
}
static int
dirname(Dir *d, char buf[Maxpath])
{
char c, *x;
if(d->attr == 0x0F || *d->name <= 0)
return -1;
memmove(buf, d->name, 8);
x = buf+8;
while(x > buf && x[-1] == ' ')
x--;
if(d->name[8] != ' '){
*x++ = '.';
memmove(x, d->name+8, 3);
x += 3;
}
while(x > buf && x[-1] == ' ')
x--;
*x = 0;
x = buf;
while(c = *x){
if(c >= 'A' && c <= 'Z'){
c -= 'A';
c += 'a';
}
*x++ = c;
}
return x - buf;
}
static ulong
dirclust(Dir *d)
{
return *((ushort*)d->starthi)<<16 | *((ushort*)d->startlo);
}
static void
fileinit(File *fp, Fat *fat, ulong lba)
{
fp->fat = fat;
fp->lba = lba;
fp->len = 0;
fp->lbaoff = 0;
fp->clust = ~0U;
fp->rp = fp->ep = fp->buf + Sectsz;
}
static int
fatwalk(File *fp, Fat *fat, char *path)
{
char name[Maxpath], *end;
int i, j;
Dir d;
if(fat->ver == Fat32){
fileinit(fp, fat, 0);
fp->clust = fat->dirstart;
fp->len = ~0U;
}else{
fileinit(fp, fat, fat->dirstart);
fp->len = fat->dirents * Dirsz;
}
for(;;){
if(readn(fp, &d, Dirsz) != Dirsz)
break;
if((i = dirname(&d, name)) <= 0)
continue;
while(*path == '/')
path++;
if((end = strchr(path, '/')) == 0)
end = path + strlen(path);
j = end - path;
if(i == j && memcmp(name, path, j) == 0){
fileinit(fp, fat, 0);
fp->clust = dirclust(&d);
fp->len = GETLONG(d.len);
if(*end == 0)
return 0;
else if(d.attr & 0x10){
fp->len = fat->clustsize * Sectsz;
path = end;
continue;
}
break;
}
}
return -1;
}
static int
conffat(Fat *fat, void *buf)
{
Pbs *p = buf;
uint fatsize, volsize, datasize, reserved;
uint ver, dirsize, dirents, clusters;
if(GETSHORT(p->sectsize) != Sectsz)
return -1;
if(memcmp(p->type, "FAT", 3) && memcmp(((Pbs32*)buf)->type, "FAT", 3))
return -1;
/* load values from fat */
ver = 0;
fatsize = GETSHORT(p->fatsize);
if(fatsize == 0){
fatsize = GETLONG(((Pbs32*)buf)->fatsize);
ver = Fat32;
}
volsize = GETSHORT(p->volsize);
if(volsize == 0)
volsize = GETLONG(p->bigvolsize);
reserved = GETSHORT(p->nreserv);
dirents = GETSHORT(p->rootsize);
dirsize = (dirents * Dirsz + Sectsz - 1) / Sectsz;
datasize = volsize - (reserved + fatsize * p->nfats + dirsize);
clusters = datasize / p->clustsize;
if(ver != Fat32)
if(clusters < 0xff7)
ver = Fat12;
else
ver = Fat16;
/* fill FAT descriptor */
fat->ver = ver;
fat->dirents = dirents;
fat->clustsize = p->clustsize;
fat->fatlba = fat->partlba + reserved;
fat->dirstart = fat->fatlba + fatsize * p->nfats;
if(ver == Fat32){
fat->datalba = fat->dirstart;
fat->dirstart = GETLONG(((Pbs32*)buf)->rootclust);
fat->eofmark = 0xffffff7;
}else{
fat->datalba = fat->dirstart + dirsize;
if(ver == Fat16)
fat->eofmark = 0xfff7;
else
fat->eofmark = 0xff7;
}
return 0;
}
static int
findfat(Fat *fat, int drive, ulong xbase, ulong lba)
{
struct {
uchar status;
uchar bchs[3];
uchar typ;
uchar echs[3];
uchar lba[4];
uchar len[4];
} p[4];
uchar buf[Sectsz];
int i;
if(xbase == 0)
xbase = lba;
if(readsect(drive, lba, buf))
return -1;
if(buf[0x1fe] != 0x55 || buf[0x1ff] != 0xAA)
return -1;
if(lba == 0 && (drive & 0x80) == 0){ /* floppy */
fat->drive = drive;
fat->partlba = 0;
if(!conffat(fat, buf))
return 0;
}
memmove(p, &buf[0x1be], sizeof(p));
for(i=0; i<4; i++){
switch(p[i].typ){
case 0x05:
case 0x0f:
case 0x85:
/* extended partitions */
if(!findfat(fat, drive, xbase, xbase + GETLONG(p[i].lba)))
return 0;
/* no break */
case 0x00:
continue;
default:
if(p[i].status != 0x80)
continue;
case 0x39: /* always try plan9 partition */
fat->drive = drive;
fat->partlba = lba + GETLONG(p[i].lba);
if(readsect(drive, fat->partlba, buf))
continue;
if(!conffat(fat, buf))
return 0;
}
}
return -1;
}
void
start(void *sp)
{
char path[Maxpath], *kern;
int drive;
File fi;
Fat fat;
void *f;
/* drive passed in DL */
drive = ((ushort*)sp)[5] & 0xFF;
if(findfat(&fat, drive, 0, 0)){
print("no fat\n");
halt();
}
if(fatwalk(f = &fi, &fat, "plan9.ini")){
print("no config\n");
f = 0;
}
for(;;){
kern = configure(f, path); f = 0;
if(fatwalk(&fi, &fat, kern)){
print("not found\n");
continue;
}
print(bootkern(&fi));
print("\n");
}
}