dossubs.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

			return -1;
		for(o=0; o<bp->sectsize; o+=DOSDIRSIZE){
			d = (Dosdir *)&p->iobuf[o];
			if(d->name[0] == 0x00){
				putsect(p);
				return 0;
			}
			if(d->name[0] == DOSEMPTY)
				continue;
			if(d->name[0] == '.')
				continue;
			if(d->attr&DVLABEL)
				continue;
			putsect(p);
			return -1;
		}
		putsect(p);
	}
	return 0;
}

long
readdir(Xfile *f, void *vbuf, long offset, long count)
{
	Xfs *xf;
	Dosbpb *bp;
	Dir dir;
	int isect, addr, o, islong, sum;
	Iosect *p;
	Dosdir *d;
	long rcnt, n;
	char *name, snamebuf[8+1+3+1], namebuf[DOSNAMELEN];
	uchar *buf;

	buf = vbuf;
	rcnt = 0;
	xf = f->xf;
	bp = xf->ptr;
	if(count <= 0)
		return 0;
	islong = 0;
	sum = -1;
	name = nil;
	for(isect=0;; isect++){
		addr = fileaddr(f, isect, 0);
		if(addr < 0)
			break;
		p = getsect(xf, addr);
		if(p == 0)
			return -1;
		for(o=0; o<bp->sectsize; o+=DOSDIRSIZE){
			d = (Dosdir *)&p->iobuf[o];
			if(d->name[0] == 0x00){
				putsect(p);
				return rcnt;
			}
			if(d->name[0] == DOSEMPTY)
				continue;
			dirdump(d);
			if(d->name[0] == '.'){
				if(d->name[1] == ' ' || d->name[1] == 0)
					continue;
				if(d->name[1] == '.' &&
				  (d->name[2] == ' ' || d->name[2] == 0))
					continue;
			}
			if((d->attr & 0xf) == 0xf){
				name = getnamesect(namebuf, name, p->iobuf+o, &islong, &sum, 1);
				continue;
			}
			if(d->attr & DVLABEL){
				islong = 0;
				continue;
			}
			dir.name = snamebuf;
			getdir(xf, &dir, d, addr, o);
			if(islong == 1 && nameok(name) && sum == aliassum(d))
				dir.name = name;
			islong = 0;
			n = convD2M(&dir, &buf[rcnt], count - rcnt);
			name = nil;
			if(n <= BIT16SZ){	/* no room for next entry */
				putsect(p);
				return rcnt;
			}
			rcnt += n;
			if(offset > 0){
				offset -= rcnt;
				rcnt = 0;
				islong = 0;
				continue;
			}
			if(rcnt == count){
				putsect(p);
				return rcnt;
			}
		}
		putsect(p);
	}
	return rcnt;
}

/*
 * set up ndp for a directory's parent
 * the hardest part is setting up paddr
 */
int
walkup(Xfile *f, Dosptr *ndp)
{
	Dosbpb *bp;
	Dosptr *dp;
	Dosdir *xd;
	Iosect *p;
	long k, o, so, start, pstart, ppstart, st, ppclust;

	bp = f->xf->ptr;
	dp = f->ptr;
	memset(ndp, 0, sizeof(Dosptr));
	ndp->prevaddr = -1;
	ndp->naddr = -1;
	ndp->addr = dp->paddr;
	ndp->offset = dp->poffset;

	chat("walkup: paddr=%#lx...", dp->paddr);

	/*
	 * root's paddr is always itself
	 */
	if(isroot(dp->paddr))
		return 0;

	/*
	 * find the start of our parent's directory
	 */
	p = getsect(f->xf, dp->paddr);
	if(p == nil)
		goto error;
	xd = (Dosdir *)&p->iobuf[dp->poffset];
	dirdump(xd);
	start = getstart(f->xf, xd);
	chat("start=%#lx...", start);
	if(start == 0)
		goto error;
	putsect(p);

	/*
	 * verify that parent's . points to itself
	 */
	p = getsect(f->xf, clust2sect(bp, start));
	if(p == nil)
		goto error;
	xd = (Dosdir *)p->iobuf;
	dirdump(xd);
	st = getstart(f->xf, xd);
	if(xd->name[0]!='.' || xd->name[1]!=' ' || start!=st)
		goto error;

	/*
	 * parent's .. is the next entry, and has start of parent's parent
	 */
	xd++;
	dirdump(xd);
	if(xd->name[0] != '.' || xd->name[1] != '.')
		goto error;
	pstart = getstart(f->xf, xd);
	putsect(p);

	/*
	 * we're done if parent is root
	 */
	if(pstart == 0 || f->xf->isfat32 && pstart == bp->rootstart)
		return 0;

	/*
	 * verify that parent's . points to itself
	 */
	p = getsect(f->xf, clust2sect(bp, pstart));
	if(p == 0){
		chat("getsect %ld failed\n", pstart);
		goto error;
	}
	xd = (Dosdir *)p->iobuf;
	dirdump(xd);
	st = getstart(f->xf, xd);
	if(xd->name[0]!='.' || xd->name[1]!=' ' || pstart!=st)
		goto error;

	/*
	 * parent's parent's .. is the next entry, and has start of parent's parent's parent
	 */
	xd++;
	dirdump(xd);
	if(xd->name[0] != '.' || xd->name[1] != '.')
		goto error;
	ppstart = getstart(f->xf, xd);
	putsect(p);

	/*
	 * open parent's parent's parent, and walk through it until parent's parent is found
	 * need this to find parent's parent's addr and offset
	 */
	ppclust = ppstart;
	if(f->xf->isfat32 && ppclust == 0){
		ppclust = bp->rootstart;
		chat("ppclust 0, resetting to rootstart\n");
	}
	k = ppclust ? clust2sect(bp, ppclust) : bp->rootaddr;
	p = getsect(f->xf, k);
	if(p == nil){
		chat("getsect %ld failed\n", k);
		goto error;
	}
	xd = (Dosdir *)p->iobuf;
	dirdump(xd);
	if(ppstart){
		st = getstart(f->xf, xd);
		if(xd->name[0]!='.' || xd->name[1]!=' ' || ppstart!=st)
			goto error;
	}
	for(so=1;; so++){
		for(o=0; o<bp->sectsize; o+=DOSDIRSIZE){
			xd = (Dosdir *)&p->iobuf[o];
			if(xd->name[0] == 0x00){
				chat("end dir\n");
				goto error;
			}
			if(xd->name[0] == DOSEMPTY)
				continue;
			st = getstart(f->xf, xd);
			if(st == pstart)
				goto out;
		}
		if(ppclust){
			if(so%bp->clustsize == 0){
				mlock(bp);
				ppclust = getfat(f->xf, ppclust);
				unmlock(bp);
				if(ppclust < 0){
					chat("getfat %ld failed\n", ppclust);
					goto error;
				}
			}
			k = clust2sect(bp, ppclust) + 
				so%bp->clustsize;
		}else{
			if(so*bp->sectsize >= bp->rootsize*DOSDIRSIZE)
				goto error;
			k = bp->rootaddr + so;
		}
		putsect(p);
		p = getsect(f->xf, k);
		if(p == 0){
			chat("getsect %ld failed\n", k);
			goto error;
		}
	}
out:
	putsect(p);
	ndp->paddr = k;
	ndp->poffset = o;
	return 0;

error:
	if(p)
		putsect(p);
	return -1;
}

long
readfile(Xfile *f, void *vbuf, long offset, long count)
{
	Xfs *xf = f->xf;
	Dosbpb *bp = xf->ptr;
	Dosptr *dp = f->ptr;
	Dosdir *d = dp->d;
	int isect, addr, o, c;
	Iosect *p;
	uchar *buf;
	long length, rcnt;

	rcnt = 0;
	length = GLONG(d->length);
	buf = vbuf;
	if(offset >= length)
		return 0;
	if(offset+count >= length)
		count = length - offset;
	isect = offset/bp->sectsize;
	o = offset%bp->sectsize;
	while(count > 0){
		addr = fileaddr(f, isect++, 0);
		if(addr < 0)
			break;
		c = bp->sectsize - o;
		if(c > count)
			c = count;
		p = getsect(xf, addr);
		if(p == 0)
			return -1;
		memmove(&buf[rcnt], &p->iobuf[o], c);
		putsect(p);
		count -= c;
		rcnt += c;
		o = 0;
	}
	return rcnt;
}

long
writefile(Xfile *f, void *vbuf, long offset, long count)
{
	Xfs *xf = f->xf;
	Dosbpb *bp = xf->ptr;
	Dosptr *dp = f->ptr;
	Dosdir *d = dp->d;
	int isect, addr = 0, o, c;
	Iosect *p;
	uchar *buf;
	long length, rcnt = 0, dlen;

	buf = vbuf;
	isect = offset/bp->sectsize;
	o = offset%bp->sectsize;
	while(count > 0){
		addr = fileaddr(f, isect++, 1);
		if(addr < 0)
			break;
		c = bp->sectsize - o;
		if(c > count)
			c = count;
		if(c == bp->sectsize){
			p = getosect(xf, addr);
			p->flags = 0;
		}else{
			p = getsect(xf, addr);
			if(p == nil)
				return -1;
		}
		memmove(&p->iobuf[o], &buf[rcnt], c);
		p->flags |= BMOD;
		putsect(p);
		count -= c;
		rcnt += c;
		o = 0;
	}
	if(rcnt <= 0 && addr < 0)
		return -1;
	length = 0;
	dlen = GLONG(d->length);
	if(rcnt > 0)
		length = offset+rcnt;
	else if(dp->addr && dp->clust){
		c = bp->clustsize*bp->sectsize;
		if(dp->iclust > (dlen+c-1)/c)
			length = c*dp->iclust;
	}
	if(length > dlen)
		PLONG(d->length, length);
	puttime(d, 0);
	dp->p->flags |= BMOD;
	return rcnt;
}

int
truncfile(Xfile *f, long length)
{
	Xfs *xf = f->xf;
	Dosbpb *bp = xf->ptr;
	Dosptr *dp = f->ptr;
	Dosdir *d = dp->d;
	long clust, next, n;

	mlock(bp);
	clust = getstart(f->xf, d);
	n = length;
	if(n <= 0)
		putstart(f->xf, d, 0);
	else
		n -= bp->sectsize;
	while(clust > 0){
		next = getfat(xf, clust);
		if(n <= 0)
			putfat(xf, clust, 0);
		else
			n -= bp->clustsize*bp->sectsize;
		clust = next;
	}
	unmlock(bp);
	PLONG(d->length, length);
	dp->iclust = 0;
	dp->clust = 0;
	dp->p->flags |= BMOD;
	return 0;
}

void
putdir(Dosdir *d, Dir *dp)
{
	if(dp->mode != ~0){
		if(dp->mode & 2)
			d->attr &= ~DRONLY;
		else
			d->attr |= DRONLY;
		if(dp->mode & DMEXCL)
			d->attr |= DSYSTEM;
		else
			d->attr &= ~DSYSTEM;
	}
	if(dp->mtime != ~0)
		puttime(d, dp->mtime);
}

/*
 * should extend this to deal with
 * creation and access dates
 */
void
getdir(Xfs *xfs, Dir *dp, Dosdir *d, int addr, int offset)
{
	if(d == nil || addr == 0)
		panic("getdir on root");
	dp->type = 0;
	dp->dev = 0;
	getname(dp->name, d);

	dp->qid.path = addr*(Sectorsize/DOSDIRSIZE) +
			offset/DOSDIRSIZE;
	dp->qid.vers = 0;

	if(d->attr & DRONLY)
		dp->mode = 0444;
	else
		dp->mode = 0666;
	dp->atime = gtime(d);
	dp->mtime = dp->atime;
	dp->qid.type = QTFILE;
	if(d->attr & DDIR){
		dp->qid.type = QTDIR;
		dp->mode |= DMDIR|0111;
		dp->length = 0;
	}else
		dp->length = GLONG(d->length);
	if(d->attr & DSYSTEM){
		dp->mode |= DMEXCL;
		if(iscontig(xfs, d))
			dp->mode |= DMAPPEND;
	}

	dp->uid = "bill";
	dp->muid = "bill";
	dp->gid = "trog";
}

void
getname(char *p, Dosdir *d)
{
	int c, i;

	for(i=0; i<8; i++){
		c = d->name[i];
		if(c == '\0' || c == ' ')
			break;
		if(i == 0 && c == 0x05)
			c = 0xe5;
		*p++ = c;
	}
	for(i=0; i<3; i++){
		c = d->ext[i];
		if(c == '\0' || c == ' ')
			break;
		if(i == 0)
			*p++ = '.';
		*p++ = c;
	}
	*p = 0;
}

static char*
getnamerunes(char *dst, uchar *buf, int step)
{
	int i;
	Rune r;
	char dbuf[DOSRUNE * UTFmax + 1], *d;

	d = dbuf;
	r = 1;
	for(i = 1; r && i < 11; i += 2){
		r = buf[i] | (buf[i+1] << 8);
		d += runetochar(d, &r);
	}
	for(i = 14; r && i < 26; i += 2){
		r = buf[i] | (buf[i+1] << 8);
		d += runetochar(d, &r);
	}
	for(i = 28; r && i < 32; i += 2){
		r = buf[i] | (buf[i+1] << 8);
		d += runetochar(d, &r);
	}

	if(step == 1)
		dst -= d - dbuf;

	memmove(dst, dbuf, d - dbuf);

	if(step == -1){
		dst += d - dbuf;
		*dst = '\0';
	}

	return dst;
}

char*
getnamesect(char *dbuf, char *d, uchar *buf, int *islong, int *sum, int step)
{
	/*
	 * validation checks to make sure we're
	 * making up a consistent name
	 */
	if(buf[11] != 0xf || buf[12] != 0){
		*islong = 0;
		return nil;
	}
	if(step == 1){
		if((buf[0] & 0xc0) == 0x40){
			*islong = buf[0] & 0x3f;
			*sum = buf[13];
			d = dbuf + DOSNAMELEN;
			*--d = '\0';
		}else if(*islong && *islong == buf[0] + 1 && *sum == buf[13]){
			*islong = buf[0];
		}else{
			*islong = 0;
			return nil;
		}
	}else{
		if(*islong + 1 == (buf[0] & 0xbf) && *sum == buf[13]){
			*islong = buf[0] & 0x3f;
			if(buf[0] & 0x40)
				*sum = -1;
		}else{
			*islong = 0;
			*sum = -1;
			return nil;
		}
	}
	if(*islong > 20){
		*islong = 0;
		*sum = -1;
		return nil;
	}

	return getnamerunes(d, buf, step);
}

void
putname(char *p, Dosdir *d)
{
	int i;

	memset(d->name, ' ', sizeof d->name+sizeof d->ext);
	for(i=0; i<sizeof d->name; i++){
		if(*p == 0 || *p == '.')
			break;
		d->name[i] = toupper(*p++);
	}
	p = strrchr(p, '.');
	if(p){
		for(i=0; i<sizeof d->ext; i++){
			if(*++p == 0)
				break;
			d->ext[i] = toupper(*p);
		}
	}
}

static void
putnamesect(uchar *slot, Rune *longname, int curslot, int first, int sum)
{
	Rune r;
	Dosdir ds;
	int i, j;

	memset(&ds, 0xff, sizeof ds);
	ds.attr = 0xf;
	ds.reserved[0] = 0;
	ds.reserved[1] = sum;
	ds.start[0] = 0;
	ds.start[1] = 0;
	if(first)
		ds.name[0] = 0x40 | curslot;
	else 
		ds.name[0] = curslot;
	memmove(slot, &ds, sizeof ds);

	j = (curslot-1) * DOSRUNE;

	for(i = 1; i < 11; i += 2){
		r = longname[j++];
		slot[i] = r;
		slot[i+1] = r >> 8;
		if(r == 0)
			return;
	}
	for(i = 14; i < 26; i += 2){
		r = longname[j++];
		slot[i] = r;
		slot[i+1] = r >> 8;
		if(r == 0)
			return;
	}
	for(i = 28; i < 32; i += 2){
		r = longname[j++];
		slot[i] = r;
		slot[i+1] = r >> 8;
		if(r == 0)
			return;
	}
}

int
aliassum(Dosdir *d)
{
	int i, sum;

	if(d == nil)
		return -1;
	sum = 0;
	for(i = 0; i < 11; i++)
		sum = (((sum&1)<<7) | ((sum&0xfe)>>1)) + d->name[i];
	return sum & 0xff;
}

int
putlongname(Xfs *xf, Dosptr *ndp, char *name, char sname[13])
{
	Dosbpb *bp;
	Dosdir tmpd;
	Rune longname[DOSNAMELEN+1];
	int i, first, sum, nds, len;

	/* calculate checksum */
	putname(sname, &tmpd);
	sum = aliassum(&tmpd);