ref: d540dcf6834b4bec8a2d21f2fe95eccf49f97b03
dir: /os/boot/mpc/dosboot.c/
#include "u.h"
#include "lib.h"
#include "mem.h"
#include "dat.h"
#include "fns.h"
#include "dosfs.h"
extern char *premature;
/*
* predeclared
*/
static void bootdump(Dosboot*);
static void setname(Dosfile*, char*);
long dosreadseg(Dosfile*, long, long);
/*
* debugging
*/
#define chatty 1
#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)
{
Clustbuf *p, *oldest;
int size;
chat("getclust @ %d\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 %d 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
*/
chat("getclust addr %d\n", (sector+dos->start)*dos->sectsize);
if((*dos->seek)(dos->dev, (sector+dos->start)*dos->sectsize) < 0){
chat("can't seek block\n");
return 0;
}
if((*dos->read)(dos->dev, p->iobuf, size) != size){
chat("can't read block\n");
return 0;
}
p->age = m->ticks;
p->dos = dos;
p->sector = sector;
chat("getclust %d 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;
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 |= 0xf000;
}
k = k < 0xfff8 ? k : -1;
chat("fatwalk %d -> %d\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 %d\n", fp->name, ltarget);
/*
* root directory is contiguous and easy
*/
if(fp->pstart == 0){
if(ltarget*dos->sectsize*dos->clustsize >= dos->rootsize*sizeof(Dosdir))
return -1;
l = dos->rootaddr + ltarget*dos->clustsize;
chat("fileaddr %d -> %d\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 %d -> %d\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 & DDIR) == 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(Dosfile *file, char *name)
{
Dosdir d;
long n;
if((file->attr & DDIR) == 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", d.name, 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 & DVLABEL){
chat("%8.8s.%3.3s is a LABEL\n", d.name, d.ext);
continue;
}
file->attr = d.attr;
file->pstart = GSHORT(d.start);
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 dos file system properties
*/
int
dosinit(Dos *dos, int start, int ishard)
{
Dosboot *b;
int i;
Clustbuf *p;
Dospart *dp;
ulong mbroffset, offset;
/* defaults till we know better */
dos->start = start;
dos->sectsize = 512;
dos->clustsize = 1;
mbroffset = 0;
dmddo:
/* get first sector */
p = getclust(dos, mbroffset);
if(p == 0){
chat("can't read boot block\n");
return -1;
}
/*
* If it's a hard disc then look for an MBR and pick either an
* active partition or the FAT with the lowest starting LBA.
* Things are tricky because we could be pointing to, amongst others:
* 1) a floppy BPB;
* 2) a hard disc MBR;
* 3) a hard disc extended partition table;
* 4) a logical drive on a hard disc;
* 5) a disc-manager boot block.
* They all have the same magic at the end of the block.
*/
if(p->iobuf[0x1FE] != 0x55 || p->iobuf[0x1FF] != 0xAA) {
chat("not DOS\n");
return -1;
}
p->dos = 0;
b = (Dosboot *)p->iobuf;
if(ishard && b->mediadesc != 0xF8){
dp = (Dospart*)&p->iobuf[0x1BE];
offset = 0xFFFFFFFF;
for(i = 0; i < 4; i++, dp++){
if(dp->type == DMDDO){
mbroffset = 63;
goto dmddo;
}
if(dp->type != FAT12 && dp->type != FAT16 && dp->type != FATHUGE)
continue;
if(dp->flag & 0x80){
offset = GLONG(dp->start);
break;
}
if(GLONG(dp->start) < offset)
offset = GLONG(dp->start);
}
if(i != 4 || offset != 0xFFFFFFFF){
dos->start = mbroffset+offset;
p = getclust(dos, 0);
if(p == 0 || p->iobuf[0x1FE] != 0x55 || p->iobuf[0x1FF] != 0xAA)
return -1;
}
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\n");
return -1;
}
if(chatty)
bootdump(b);
/*
* determine the systems' wondersous properties
*/
dos->sectsize = GSHORT(b->sectsize);
dos->clustsize = b->clustsize;
dos->clustbytes = dos->sectsize*dos->clustsize;
dos->nresrv = GSHORT(b->nresrv);
dos->nfats = b->nfats;
dos->rootsize = GSHORT(b->rootsize);
dos->volsize = GSHORT(b->volsize);
if(dos->volsize == 0)
dos->volsize = GLONG(b->bigvolsize);
dos->mediadesc = b->mediadesc;
dos->fatsize = GSHORT(b->fatsize);
dos->fataddr = dos->nresrv;
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->fatclusters < 4087)
dos->fatbits = 12;
else
dos->fatbits = 16;
dos->freeptr = 2;
/*
* set up the root
*/
dos->root.dos = dos;
dos->root.pstart = 0;
dos->root.pcurrent = dos->root.lcurrent = 0;
dos->root.offset = 0;
dos->root.attr = DDIR;
dos->root.length = dos->rootsize*sizeof(Dosdir);
return 0;
}
static void
bootdump(Dosboot *b)
{
if(chatty == 0)
return;
print("magic: 0x%2.2x 0x%2.2x 0x%2.2x\n",
b->magic[0], b->magic[1], b->magic[2]);
print("version: \"%8.8s\"\n", b->version);
print("sectsize: %d\n", GSHORT(b->sectsize));
print("allocsize: %d\n", b->clustsize);
print("nresrv: %d\n", GSHORT(b->nresrv));
print("nfats: %d\n", b->nfats);
print("rootsize: %d\n", GSHORT(b->rootsize));
print("volsize: %d\n", GSHORT(b->volsize));
print("mediadesc: 0x%2.2x\n", b->mediadesc);
print("fatsize: %d\n", GSHORT(b->fatsize));
print("trksize: %d\n", GSHORT(b->trksize));
print("nheads: %d\n", GSHORT(b->nheads));
print("nhidden: %d\n", 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);
}
/*
* grab next element from a path, return the pointer to unprocessed portion of
* path.
*/
static char *
nextelem(char *path, char *elem)
{
int i;
while(*path == '/')
path++;
if(*path==0 || *path==' ')
return 0;
for(i=0; *path!='\0' && *path!='/' && *path!=' '; i++){
if(i==28){
print("name component too long\n");
return 0;
}
*elem++ = *path++;
}
*elem = '\0';
return path;
}
int
dosstat(Dos *dos, char *path, Dosfile *f)
{
char element[NAMELEN];
*f = dos->root;
while(path = nextelem(path, element)){
switch(doswalk(f, element)){
case -1:
return -1;
case 0:
return 0;
}
}
return 1;
}
/*
* boot
*/
int
dosboot(Dos *dos, char *path)
{
Dosfile file;
long n;
long addr;
Exec *ep;
void (*b)(void);
switch(dosstat(dos, path, &file)){
case -1:
print("error walking to %s\n", path);
return -1;
case 0:
print("%s not found\n", path);
return -1;
case 1:
print("found %8.8s.%3.3s attr 0x%ux start 0x%lux len %d\n", file.name,
file.ext, file.attr, file.pstart, file.length);
break;
}
/*
* read header
*/
ep = (Exec*)ialloc(sizeof(Exec), 0);
n = sizeof(Exec);
if(dosreadseg(&file, n, (ulong) ep) != n){
print(premature);
return -1;
}
if(GLLONG(ep->magic) != Q_MAGIC){
print("bad magic 0x%lux not a plan 9 executable!\n", GLLONG(ep->magic));
return -1;
}
/*
* read text
*/
addr = PADDR(GLLONG(ep->entry));
n = GLLONG(ep->text);
print("+%d", n);
if(dosreadseg(&file, n, addr) != n){
print(premature);
return -1;
}
/*
* read data (starts at first page after kernel)
*/
addr = PGROUND(addr+n);
n = GLLONG(ep->data);
print("+%d", n);
if(dosreadseg(&file, n, addr) != n){
print(premature);
return -1;
}
/*
* bss and entry point
*/
print("+%d\nstart at 0x%lux\n", GLLONG(ep->bss), GLLONG(ep->entry));
/*
* Go to new code. It's up to the program to get its PC relocated to
* the right place.
*/
b = (void (*)(void))(PADDR(GLLONG(ep->entry)));
(*b)();
return 0;
}
/*
* read in a segment
*/
long
dosreadseg(Dosfile *fp, long len, long addr)
{
char *a;
long n, sofar;
a = (char *)addr;
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;
}
/*
* 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++ = ' ';
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);
}