ref: 75c92428225428c8fde2d015f010e608a0b12f1d
dir: /os/boot/pc/dosboot.c/
#include "u.h"
#include "lib.h"
#include "mem.h"
#include "dat.h"
#include "fns.h"
#include "fs.h"
struct Dosboot{
uchar magic[3];
uchar version[8];
uchar sectsize[2];
uchar clustsize;
uchar nresrv[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];
/* fat 32 */
uchar bigfatsize[4];
uchar extflags[2];
uchar fsversion[2];
uchar rootdirstartclust[4];
uchar fsinfosect[2];
uchar backupbootsect[2];
/* ???
uchar driveno;
uchar reserved0;
uchar bootsig;
uchar volid[4];
uchar label[11];
uchar reserved1[8];
*/
};
struct Dosdir{
uchar name[8];
uchar ext[3];
uchar attr;
uchar lowercase;
uchar hundredth;
uchar ctime[2];
uchar cdate[2];
uchar adate[2];
uchar highstart[2];
uchar mtime[2];
uchar mdate[2];
uchar start[2];
uchar length[4];
};
#define DOSRONLY 0x01
#define DOSHIDDEN 0x02
#define DOSSYSTEM 0x04
#define DOSVLABEL 0x08
#define DOSDIR 0x10
#define DOSARCH 0x20
/*
* predeclared
*/
static void bootdump(Dosboot*);
static void setname(Dosfile*, char*);
/*
* debugging
*/
#define chatty 0
#define chat if(chatty)print
/*
* block io buffers
*/
enum
{
Nbio= 16,
};
typedef struct Clustbuf Clustbuf;
struct Clustbuf
{
int age;
long sector;
uchar *iobuf;
Dos *dos;
int size;
};
Clustbuf bio[Nbio];
/*
* get an io block from an io buffer
*/
Clustbuf*
getclust(Dos *dos, long sector)
{
Fs *fs;
Clustbuf *p, *oldest;
int size;
chat("getclust @ %ld\n", sector);
/*
* if we have it, just return it
*/
for(p = bio; p < &bio[Nbio]; p++){
if(sector == p->sector && dos == p->dos){
p->age = m->ticks;
chat("getclust %ld in cache\n", sector);
return p;
}
}
/*
* otherwise, reuse the oldest entry
*/
oldest = bio;
for(p = &bio[1]; p < &bio[Nbio]; p++){
if(p->age <= oldest->age)
oldest = p;
}
p = oldest;
/*
* make sure the buffer is big enough
*/
size = dos->clustsize*dos->sectsize;
if(p->iobuf==0 || p->size < size)
p->iobuf = ialloc(size, 0);
p->size = size;
/*
* read in the cluster
*/
fs = (Fs*)dos;
chat("getclust addr %lud %p %p %p\n", (ulong)((sector+dos->start)*(vlong)dos->sectsize),
fs, fs->diskseek, fs->diskread);
if(fs->diskseek(fs, (sector+dos->start)*(vlong)dos->sectsize) < 0){
chat("can't seek block\n");
return 0;
}
if(fs->diskread(fs, p->iobuf, size) != size){
chat("can't read block\n");
return 0;
}
p->age = m->ticks;
p->dos = dos;
p->sector = sector;
chat("getclust %ld read\n", sector);
return p;
}
/*
* walk the fat one level ( n is a current cluster number ).
* return the new cluster number or -1 if no more.
*/
static long
fatwalk(Dos *dos, int n)
{
ulong k, sect;
Clustbuf *p;
int o;
chat("fatwalk %d\n", n);
if(n < 2 || n >= dos->fatclusters)
return -1;
switch(dos->fatbits){
case 12:
k = (3*n)/2; break;
case 16:
k = 2*n; break;
case 32:
k = 4*n; break;
default:
return -1;
}
if(k >= dos->fatsize*dos->sectsize)
panic("getfat");
sect = (k/(dos->sectsize*dos->clustsize))*dos->clustsize + dos->fataddr;
o = k%(dos->sectsize*dos->clustsize);
p = getclust(dos, sect);
k = p->iobuf[o++];
if(o >= dos->sectsize*dos->clustsize){
p = getclust(dos, sect+dos->clustsize);
o = 0;
}
k |= p->iobuf[o++]<<8;
if(dos->fatbits == 12){
if(n&1)
k >>= 4;
else
k &= 0xfff;
if(k >= 0xff8)
k = -1;
}
else if (dos->fatbits == 32){
if(o >= dos->sectsize*dos->clustsize){
p = getclust(dos, sect+dos->clustsize);
o = 0;
}
k |= p->iobuf[o++]<<16;
k |= p->iobuf[o]<<24;
if (k >= 0xfffffff8)
k = -1;
}
else
k = k < 0xfff8 ? k : -1;
chat("fatwalk %d -> %lud\n", n, k);
return k;
}
/*
* map a file's logical cluster address to a physical sector address
*/
static long
fileaddr(Dosfile *fp, long ltarget)
{
Dos *dos = fp->dos;
long l;
long p;
chat("fileaddr %8.8s %ld\n", fp->name, ltarget);
/*
* root directory is contiguous and easy (unless FAT32)
*/
if(fp->pstart == 0 && dos->rootsize != 0) {
if(ltarget*dos->sectsize*dos->clustsize >= dos->rootsize*sizeof(Dosdir))
return -1;
l = dos->rootaddr + ltarget*dos->clustsize;
chat("fileaddr %ld -> %ld\n", ltarget, l);
return l;
}
/*
* anything else requires a walk through the fat
*/
if(ltarget >= fp->lcurrent && fp->pcurrent){
/* start at the currrent point */
l = fp->lcurrent;
p = fp->pcurrent;
} else {
/* go back to the beginning */
l = 0;
p = fp->pstart;
}
while(l != ltarget){
/* walk the fat */
p = fatwalk(dos, p);
if(p < 0)
return -1;
l++;
}
fp->lcurrent = l;
fp->pcurrent = p;
/*
* clusters start at 2 instead of 0 (why? - presotto)
*/
l = dos->dataaddr + (p-2)*dos->clustsize;
chat("fileaddr %ld -> %ld\n", ltarget, l);
return l;
}
/*
* read from a dos file
*/
long
dosread(Dosfile *fp, void *a, long n)
{
long addr;
long rv;
int i;
int off;
Clustbuf *p;
uchar *from, *to;
if((fp->attr & DOSDIR) == 0){
if(fp->offset >= fp->length)
return 0;
if(fp->offset+n > fp->length)
n = fp->length - fp->offset;
}
to = a;
for(rv = 0; rv < n; rv+=i){
/*
* read the cluster
*/
addr = fileaddr(fp, fp->offset/fp->dos->clustbytes);
if(addr < 0)
return -1;
p = getclust(fp->dos, addr);
if(p == 0)
return -1;
/*
* copy the bytes we need
*/
off = fp->offset % fp->dos->clustbytes;
from = &p->iobuf[off];
i = n - rv;
if(i > fp->dos->clustbytes - off)
i = fp->dos->clustbytes - off;
memmove(to, from, i);
to += i;
fp->offset += i;
}
return rv;
}
/*
* walk a directory returns
* -1 if something went wrong
* 0 if not found
* 1 if found
*/
int
doswalk(File *f, char *name)
{
Dosdir d;
long n;
Dosfile *file;
chat("doswalk %s\n", name);
file = &f->dos;
if((file->attr & DOSDIR) == 0){
chat("walking non-directory!\n");
return -1;
}
setname(file, name);
file->offset = 0; /* start at the beginning */
while((n = dosread(file, &d, sizeof(d))) == sizeof(d)){
chat("comparing to %8.8s.%3.3s\n", (char*)d.name, (char*)d.ext);
if(memcmp(file->name, d.name, sizeof(d.name)) != 0)
continue;
if(memcmp(file->ext, d.ext, sizeof(d.ext)) != 0)
continue;
if(d.attr & DOSVLABEL){
chat("%8.8s.%3.3s is a LABEL\n", (char*)d.name, (char*)d.ext);
continue;
}
file->attr = d.attr;
file->pstart = GSHORT(d.start);
if (file->dos->fatbits == 32)
file->pstart |= GSHORT(d.highstart) << 16;
file->length = GLONG(d.length);
file->pcurrent = 0;
file->lcurrent = 0;
file->offset = 0;
return 1;
}
return n >= 0 ? 0 : -1;
}
/*
* instructions that boot blocks can start with
*/
#define JMPSHORT 0xeb
#define JMPNEAR 0xe9
/*
* read in a segment
*/
long
dosreadseg(File *f, void *va, long len)
{
char *a;
long n, sofar;
Dosfile *fp;
fp = &f->dos;
a = va;
for(sofar = 0; sofar < len; sofar += n){
n = 8*1024;
if(len - sofar < n)
n = len - sofar;
n = dosread(fp, a + sofar, n);
if(n <= 0)
break;
print(".");
}
return sofar;
}
int
dosinit(Fs *fs)
{
Clustbuf *p;
Dosboot *b;
int i;
Dos *dos;
Dosfile *root;
chat("dosinit0 %p %p %p\n", fs, fs->diskseek, fs->diskread);
dos = &fs->dos;
/* defaults till we know better */
dos->sectsize = 512;
dos->clustsize = 1;
/* get first sector */
p = getclust(dos, 0);
if(p == 0){
chat("can't read boot block\n");
return -1;
}
chat("dosinit0a\n");
p->dos = 0;
b = (Dosboot *)p->iobuf;
if(b->magic[0] != JMPNEAR && (b->magic[0] != JMPSHORT || b->magic[2] != 0x90)){
chat("no dos file system %x %x %x %x\n",
b->magic[0], b->magic[1], b->magic[2], b->magic[3]);
return -1;
}
if(chatty)
bootdump(b);
if(b->clustsize == 0) {
unreasonable:
if(chatty){
print("unreasonable FAT BPB: ");
for(i=0; i<3+8+2+1; i++)
print(" %.2ux", p->iobuf[i]);
print("\n");
}
return -1;
}
chat("dosinit1\n");
/*
* Determine the systems' wondrous properties.
* There are heuristics here, but there's no real way
* of knowing if this is a reasonable FAT.
*/
dos->fatbits = 0;
dos->sectsize = GSHORT(b->sectsize);
if(dos->sectsize & 0xFF)
goto unreasonable;
dos->clustsize = b->clustsize;
dos->clustbytes = dos->sectsize*dos->clustsize;
dos->nresrv = GSHORT(b->nresrv);
dos->nfats = b->nfats;
dos->fatsize = GSHORT(b->fatsize);
dos->rootsize = GSHORT(b->rootsize);
dos->volsize = GSHORT(b->volsize);
if(dos->volsize == 0)
dos->volsize = GLONG(b->bigvolsize);
dos->mediadesc = b->mediadesc;
if(dos->fatsize == 0) {
chat("fat32\n");
dos->rootsize = 0;
dos->fatsize = GLONG(b->bigfatsize);
dos->fatbits = 32;
}
dos->fataddr = dos->nresrv;
if (dos->rootsize == 0) {
dos->rootaddr = 0;
dos->rootclust = GLONG(b->rootdirstartclust);
dos->dataaddr = dos->fataddr + dos->nfats*dos->fatsize;
} else {
dos->rootaddr = dos->fataddr + dos->nfats*dos->fatsize;
i = dos->rootsize*sizeof(Dosdir) + dos->sectsize - 1;
i = i/dos->sectsize;
dos->dataaddr = dos->rootaddr + i;
}
dos->fatclusters = 2+(dos->volsize - dos->dataaddr)/dos->clustsize;
if(dos->fatbits != 32) {
if(dos->fatclusters < 4087)
dos->fatbits = 12;
else
dos->fatbits = 16;
}
dos->freeptr = 2;
if(dos->clustbytes < 512 || dos->clustbytes > 64*1024)
goto unreasonable;
chat("dosinit2\n");
/*
* set up the root
*/
fs->root.fs = fs;
root = &fs->root.dos;
root->dos = dos;
root->pstart = dos->rootsize == 0 ? dos->rootclust : 0;
root->pcurrent = root->lcurrent = 0;
root->offset = 0;
root->attr = DOSDIR;
root->length = dos->rootsize*sizeof(Dosdir);
chat("dosinit3\n");
fs->read = dosreadseg;
fs->walk = doswalk;
return 0;
}
static void
bootdump(Dosboot *b)
{
if(chatty == 0)
return;
print("magic: 0x%2.2x 0x%2.2x 0x%2.2x ",
b->magic[0], b->magic[1], b->magic[2]);
print("version: \"%8.8s\"\n", (char*)b->version);
print("sectsize: %d ", GSHORT(b->sectsize));
print("allocsize: %d ", b->clustsize);
print("nresrv: %d ", GSHORT(b->nresrv));
print("nfats: %d\n", b->nfats);
print("rootsize: %d ", GSHORT(b->rootsize));
print("volsize: %d ", GSHORT(b->volsize));
print("mediadesc: 0x%2.2x\n", b->mediadesc);
print("fatsize: %d ", GSHORT(b->fatsize));
print("trksize: %d ", GSHORT(b->trksize));
print("nheads: %d ", GSHORT(b->nheads));
print("nhidden: %d ", GLONG(b->nhidden));
print("bigvolsize: %d\n", GLONG(b->bigvolsize));
/*
print("driveno: %d\n", b->driveno);
print("reserved0: 0x%2.2x\n", b->reserved0);
print("bootsig: 0x%2.2x\n", b->bootsig);
print("volid: 0x%8.8x\n", GLONG(b->volid));
print("label: \"%11.11s\"\n", b->label);
*/
}
/*
* set up a dos file name
*/
static void
setname(Dosfile *fp, char *from)
{
char *to;
to = fp->name;
for(; *from && to-fp->name < 8; from++, to++){
if(*from == '.'){
from++;
break;
}
if(*from >= 'a' && *from <= 'z')
*to = *from + 'A' - 'a';
else
*to = *from;
}
while(to - fp->name < 8)
*to++ = ' ';
/* from might be 12345678.123: don't save the '.' in ext */
if(*from == '.')
from++;
to = fp->ext;
for(; *from && to-fp->ext < 3; from++, to++){
if(*from >= 'a' && *from <= 'z')
*to = *from + 'A' - 'a';
else
*to = *from;
}
while(to-fp->ext < 3)
*to++ = ' ';
chat("name is %8.8s.%3.3s\n", fp->name, fp->ext);
}