format.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

	}

	secsize = disk->secsize;
	length = disk->size;

	buf = malloc(secsize);
	if(buf == 0)
		fatal("out of memory");

	/*
	 * Make disk full size if a file.
	 */
	if(fflag && disk->type == Tfile){
		if((d = dirfstat(disk->wfd)) == nil)
			fatal("fstat disk: %r");
		if(commit && d->length < disk->size) {
			if(seek(disk->wfd, disk->size-1, 0) < 0)
				fatal("seek to 9: %r");
			if(write(disk->wfd, "9", 1) < 0)
				fatal("writing 9: @%lld %r", seek(disk->wfd, 0LL, 1));
		}
		free(d);
	}

	/*
	 * Start with initial sector from disk
	 */
	if(seek(disk->fd, 0, 0) < 0)
		fatal("seek to boot sector: %r\n");
	if(commit && read(disk->fd, buf, secsize) != secsize)
		fatal("reading boot sector: %r");

	if(dofat)
		memset(buf, 0, sizeof(Dosboot));

	/*
	 * Jump instruction and OEM name.
	 */
	b = (Dosboot*)buf;
	b->magic[0] = 0xEB;
	b->magic[1] = 0x3C;
	b->magic[2] = 0x90;
	memmove(b->version, "Plan9.00", sizeof(b->version));
	
	/*
	 * Add bootstrapping code; assume it starts 
	 * at 0x3E (the destination of the jump we just
	 * wrote to b->magic).
	 */
	if(dopbs) {
		pbsbuf = malloc(secsize);
		if(pbsbuf == 0)
			fatal("out of memory");

		if(pbs){
			if((sysfd = open(pbs, OREAD)) < 0)
				fatal("open %s: %r", pbs);
			if((npbs = read(sysfd, pbsbuf, secsize)) < 0)
				fatal("read %s: %r", pbs);

			if(npbs > secsize-2)
				fatal("boot block too large");

			close(sysfd);
		}
		else {
			memmove(pbsbuf, bootprog, sizeof(bootprog));
			npbs = nbootprog;
		}
		if(npbs <= 0x3E)
			fprint(2, "warning: pbs too small\n");
		else
			memmove(buf+0x3E, pbsbuf+0x3E, npbs-0x3E);

		free(pbsbuf);
	}

	/*
	 * Add FAT BIOS parameter block.
	 */
	if(dofat) {
		if(commit) {
			print("Initializing FAT file system\n");
			print("type %s, %d tracks, %d heads, %d sectors/track, %lld bytes/sec\n",
				t->name, t->tracks, t->heads, t->sectors, secsize);
		}

		if(clustersize == 0)
			clustersize = t->cluster;
		/*
		 * the number of fat bits depends on how much disk is left
		 * over after you subtract out the space taken up by the fat tables. 
		 * try both.  what a crock.
		 */
		fatbits = 12;
Tryagain:
		volsecs = length/secsize;
		/*
		 * here's a crock inside a crock.  even having fixed fatbits,
		 * the number of fat sectors depends on the number of clusters,
		 * but of course we don't know yet.  maybe iterating will get us there.
		 * or maybe it will cycle.
		 */
		clusters = 0;
		for(i=0;; i++){
			fatsecs = (fatbits*clusters + 8*secsize - 1)/(8*secsize);
			rootsecs = volsecs/200;
			rootfiles = rootsecs * (secsize/sizeof(Dosdir));
			if(rootfiles > 512){
				rootfiles = 512;
				rootsecs = rootfiles/(secsize/sizeof(Dosdir));
			}
			data = nresrv + 2*fatsecs + (rootfiles*sizeof(Dosdir) + secsize-1)/secsize;
			newclusters = 2 + (volsecs - data)/clustersize;
			if(newclusters == clusters)
				break;
			clusters = newclusters;
			if(i > 10)
				fatal("can't decide how many clusters to use (%d? %d?)", clusters, newclusters);
if(chatty) print("clusters %d\n", clusters);
		}
				
if(chatty) print("try %d fatbits => %d clusters of %d\n", fatbits, clusters, clustersize);
		switch(fatbits){
		case 12:
			if(clusters >= 4087){
				fatbits = 16;
				goto Tryagain;
			}
			break;
		case 16:
			if(clusters >= 65527)
				fatal("disk too big; implement fat32");
			break;
		}
		PUTSHORT(b->sectsize, secsize);
		b->clustsize = clustersize;
		PUTSHORT(b->nresrv, nresrv);
		b->nfats = 2;
		PUTSHORT(b->rootsize, rootfiles);
		if(volsecs < (1<<16))
			PUTSHORT(b->volsize, volsecs);
		b->mediadesc = t->media;
		PUTSHORT(b->fatsize, fatsecs);
		PUTSHORT(b->trksize, t->sectors);
		PUTSHORT(b->nheads, t->heads);
		PUTLONG(b->nhidden, disk->offset);
		PUTLONG(b->bigvolsize, volsecs);
	
		/*
		 * Extended BIOS Parameter Block.
		 */
		if(t->media == 0xF8)
			b->driveno = getdriveno(disk);
		else
			b->driveno = 0;
if(chatty) print("driveno = %ux\n", b->driveno);
	
		b->bootsig = 0x29;
		x = disk->offset + b->nfats*fatsecs + nresrv;
		PUTLONG(b->volid, x);
if(chatty) print("volid = %lux %lux\n", x, GETLONG(b->volid));
		memmove(b->label, label, sizeof(b->label));
		sprint(r, "FAT%d    ", fatbits);
		memmove(b->type, r, sizeof(b->type));
	}

	buf[secsize-2] = 0x55;
	buf[secsize-1] = 0xAA;

	if(commit) {
		if(seek(disk->wfd, 0, 0) < 0)
			fatal("seek to boot sector: %r\n");
		if(write(disk->wfd, buf, secsize) != secsize)
			fatal("writing boot sector: %r");
	}

	free(buf);

	/*
	 * If we were only called to write the PBS, leave now.
	 */
	if(dofat == 0)
		return;

	/*
	 *  allocate an in memory fat
	 */
	if(seek(disk->wfd, nresrv*secsize, 0) < 0)
		fatal("seek to fat: %r\n");
if(chatty) print("fat @%lluX\n", seek(disk->wfd, 0, 1));
	fat = malloc(fatsecs*secsize);
	if(fat == 0)
		fatal("out of memory");
	memset(fat, 0, fatsecs*secsize);
	fat[0] = t->media;
	fat[1] = 0xff;
	fat[2] = 0xff;
	if(fatbits == 16)
		fat[3] = 0xff;
	fatlast = 1;
	if(seek(disk->wfd, 2*fatsecs*secsize, 1) < 0)	/* 2 fats */
		fatal("seek to root: %r");
if(chatty) print("root @%lluX\n", seek(disk->wfd, 0LL, 1));

	/*
	 *  allocate an in memory root
	 */
	root = malloc(rootsecs*secsize);
	if(root == 0)
		fatal("out of memory");
	memset(root, 0, rootsecs*secsize);
	if(seek(disk->wfd, rootsecs*secsize, 1) < 0)	/* rootsecs */
		fatal("seek to files: %r");
if(chatty) print("files @%lluX\n", seek(disk->wfd, 0LL, 1));

	/*
	 * Now positioned at the Files Area.
	 * If we have any arguments, process 
	 * them and write out.
	 */
	for(p = root; argc > 0; argc--, argv++, p += sizeof(Dosdir)){
		if(p >= (root+(rootsecs*secsize)))
			fatal("too many files in root");
		/*
		 * Open the file and get its length.
		 */
		if((sysfd = open(*argv, OREAD)) < 0)
			fatal("open %s: %r", *argv);
		if((d = dirfstat(sysfd)) == nil)
			fatal("stat %s: %r", *argv);
		if(d->length > 0xFFFFFFFFU)
			fatal("file %s too big\n", *argv, d->length);
		if(commit)
			print("Adding file %s, length %lld\n", *argv, d->length);

		length = d->length;
		if(length){
			/*
			 * Allocate a buffer to read the entire file into.
			 * This must be rounded up to a cluster boundary.
			 *
			 * Read the file and write it out to the Files Area.
			 */
			length += secsize*clustersize - 1;
			length /= secsize*clustersize;
			length *= secsize*clustersize;
			if((buf = malloc(length)) == 0)
				fatal("out of memory");
	
			if(readn(sysfd, buf, d->length) != d->length)
				fatal("read %s: %r", *argv);
			memset(buf+d->length, 0, length-d->length);
if(chatty) print("%s @%lluX\n", d->name, seek(disk->wfd, 0LL, 1));
			if(commit && writen(disk->wfd, buf, length) != length)
				fatal("write %s: %r", *argv);
			free(buf);

			close(sysfd);
	
			/*
			 * Allocate the FAT clusters.
			 * We're assuming here that where we
			 * wrote the file is in sync with
			 * the cluster allocation.
			 * Save the starting cluster.
			 */
			length /= secsize*clustersize;
			x = clustalloc(Sof);
			for(n = 0; n < length-1; n++)
				clustalloc(0);
			clustalloc(Eof);
		}
		else
			x = 0;

		/*
		 * Add the filename to the root.
		 */
fprint(2, "add %s at clust %lux\n", d->name, x);
		addrname(p, d, *argv, x);
		free(d);
	}

	/*
	 *  write the fats and root
	 */
	if(commit) {
		if(seek(disk->wfd, nresrv*secsize, 0) < 0)
			fatal("seek to fat #1: %r");
		if(write(disk->wfd, fat, fatsecs*secsize) < 0)
			fatal("writing fat #1: %r");
		if(write(disk->wfd, fat, fatsecs*secsize) < 0)
			fatal("writing fat #2: %r");
		if(write(disk->wfd, root, rootsecs*secsize) < 0)
			fatal("writing root: %r");
	}

	free(fat);
	free(root);
}

/*
 *  allocate a cluster
 */
ulong
clustalloc(int flag)
{
	ulong o, x;

	if(flag != Sof){
		x = (flag == Eof) ? 0xffff : (fatlast+1);
		if(fatbits == 12){
			x &= 0xfff;
			o = (3*fatlast)/2;
			if(fatlast & 1){
				fat[o] = (fat[o]&0x0f) | (x<<4);
				fat[o+1] = (x>>4);
			} else {
				fat[o] = x;
				fat[o+1] = (fat[o+1]&0xf0) | ((x>>8) & 0x0F);
			}
		} else {
			o = 2*fatlast;
			fat[o] = x;
			fat[o+1] = x>>8;
		}
	}
		
	if(flag == Eof)
		return 0;
	else{
		++fatlast;
		if(fatlast >= clusters)
			sysfatal("data does not fit on disk (%d %d)", fatlast, clusters);
		return fatlast;
	}
}

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);
		}
	}
}

void
puttime(Dosdir *d)
{
	Tm *t = localtime(time(0));
	ushort x;

	x = (t->hour<<11) | (t->min<<5) | (t->sec>>1);
	d->time[0] = x;
	d->time[1] = x>>8;
	x = ((t->year-80)<<9) | ((t->mon+1)<<5) | t->mday;
	d->date[0] = x;
	d->date[1] = x>>8;
}

void
addrname(uchar *entry, Dir *dir, char *name, ulong start)
{
	char *s;
	Dosdir *d;

	s = strrchr(name, '/');
	if(s)
		s++;
	else
		s = name;

	d = (Dosdir*)entry;
	putname(s, d);
	if(strcmp(s, "9load") == 0)
		d->attr = DSYSTEM;
	else
		d->attr = 0;
	puttime(d);
	d->start[0] = start;
	d->start[1] = start>>8;
	d->length[0] = dir->length;
	d->length[1] = dir->length>>8;
	d->length[2] = dir->length>>16;
	d->length[3] = dir->length>>24;
}