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

#include <u.h>
#include <libc.h>
#include <ctype.h>
#include <disk.h>

/*
 *  disk types (all MFM encoding)
 */
typedef struct Type	Type;
struct Type
{
	char	*name;
	int	bytes;		/* bytes/sector */
	int	sectors;	/* sectors/track */
	int	heads;		/* number of heads */
	int	tracks;		/* tracks/disk */
	int	media;		/* media descriptor byte */
	int	cluster;	/* default cluster size */
};
Type floppytype[] =
{
 { "3½HD",	512, 18,  2, 80, 0xf0, 1, },
 { "3½DD",	512,  9,  2, 80, 0xf9, 2, },
 { "3½QD",	512, 36, 2, 80, 0xf9, 2, },	/* invented */
 { "5¼HD",	512, 15,  2, 80, 0xf9, 1, },
 { "5¼DD",	512,  9,  2, 40, 0xfd, 2, },
 { "hard",		512,  0,  0, 0, 0xf8, 4, },
};

#define NTYPES (sizeof(floppytype)/sizeof(Type))

typedef struct Dosboot	Dosboot;
struct Dosboot{
	uchar	magic[3];	/* really an x86 JMP instruction */
	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];
	uchar	driveno;
	uchar	reserved0;
	uchar	bootsig;
	uchar	volid[4];
	uchar	label[11];
	uchar	type[8];
};
#define	PUTSHORT(p, v) { (p)[1] = (v)>>8; (p)[0] = (v); }
#define	PUTLONG(p, v) { PUTSHORT((p), (v)); PUTSHORT((p)+2, (v)>>16); }
#define	GETSHORT(p)	(((p)[1]<<8)|(p)[0])
#define	GETLONG(p)	(((ulong)GETSHORT(p+2)<<16)|(ulong)GETSHORT(p))

typedef struct Dosdir	Dosdir;
struct Dosdir
{
	uchar	name[8];
	uchar	ext[3];
	uchar	attr;
	uchar	reserved[10];
	uchar	time[2];
	uchar	date[2];
	uchar	start[2];
	uchar	length[4];
};

#define	DRONLY	0x01
#define	DHIDDEN	0x02
#define	DSYSTEM	0x04
#define	DVLABEL	0x08
#define	DDIR	0x10
#define	DARCH	0x20

/*
 *  the boot program for the boot sector.
 */
int nbootprog = 188;	/* no. of bytes of boot program, including the first 0x3E */
uchar bootprog[512] =
{
[0x000]	0xEB, 0x3C, 0x90, 0x00, 0x00, 0x00, 0x00, 0x00,
	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
[0x03E] 0xFA, 0xFC, 0x8C, 0xC8, 0x8E, 0xD8, 0x8E, 0xD0,
	0xBC, 0x00, 0x7C, 0xBE, 0x77, 0x7C, 0xE8, 0x19,
	0x00, 0x33, 0xC0, 0xCD, 0x16, 0xBB, 0x40, 0x00,
	0x8E, 0xC3, 0xBB, 0x72, 0x00, 0xB8, 0x34, 0x12,
	0x26, 0x89, 0x07, 0xEA, 0x00, 0x00, 0xFF, 0xFF,
	0xEB, 0xD6, 0xAC, 0x0A, 0xC0, 0x74, 0x09, 0xB4,
	0x0E, 0xBB, 0x07, 0x00, 0xCD, 0x10, 0xEB, 0xF2,
	0xC3,  'N',  'o',  't',  ' ',  'a',  ' ',  'b',
	 'o',  'o',  't',  'a',  'b',  'l',  'e',  ' ',
	 'd',  'i',  's',  'c',  ' ',  'o',  'r',  ' ',
	 'd',  'i',  's',  'c',  ' ',  'e',  'r',  'r',
	 'o',  'r', '\r', '\n',  'P',  'r',  'e',  's',
	 's',  ' ',  'a',  'l',  'm',  'o',  's',  't',
	 ' ',  'a',  'n',  'y',  ' ',  'k',  'e',  'y',
	 ' ',  't',  'o',  ' ',  'r',  'e',  'b',  'o',
	 'o',  't',  '.',  '.',  '.', 0x00, 0x00, 0x00,
[0x1F0]	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x55, 0xAA,
};

char *dev;
int clustersize;
uchar *fat;	/* the fat */
int fatbits;
int fatsecs;
int fatlast;	/* last cluster allocated */
int clusters;
int fatsecs;
vlong volsecs;
uchar *root;	/* first block of root */
int rootsecs;
int rootfiles;
int rootnext;
int nresrv = 1;
int chatty;
vlong length;
Type *t;
int fflag;
int hflag;
int xflag;
char *file;
char *pbs;
char *type;
char *bootfile;
int dos;

enum
{
	Sof = 1,	/* start of file */
	Eof = 2,	/* end of file */
};

void	dosfs(int, int, Disk*, char*, int, char*[], int);
ulong	clustalloc(int);
void	addrname(uchar*, Dir*, char*, ulong);
void sanitycheck(Disk*);

void
usage(void)
{
	fprint(2, "usage: disk/format [-df] [-b bootblock] [-c csize] [-l label] [-r nresrv] [-t type] disk [files ...]\n");
	exits("usage");
}

void
fatal(char *fmt, ...)
{
	char err[128];
	va_list arg;

	va_start(arg, fmt);
	vsnprint(err, sizeof(err), fmt, arg);
	va_end(arg);
	fprint(2, "format: %s\n", err);
	if(fflag && file)
		remove(file);
	exits(err);
}

void
main(int argc, char **argv)
{
	int n, writepbs;
	int fd;
	char buf[512];
	char label[11];
	char *a;
	Disk *disk;

	dos = 0;
	type = nil;
	clustersize = 0;
	writepbs = 0;
	memmove(label, "CYLINDRICAL", sizeof(label));
	ARGBEGIN {
	case 'c':
		clustersize = atoi(ARGF());
		break;
	case 'd':
		dos = 1;
		writepbs = 1;
		break;
	case 'f':
		fflag = 1;
		break;
	case 'l':
		a = ARGF();
		n = strlen(a);
		if(n > sizeof(label))
			n = sizeof(label);
		memmove(label, a, n);
		while(n < sizeof(label))
			label[n++] = ' ';
		break;
	case 'b':
		pbs = ARGF();
		writepbs = 1;
		break;
	case 'r':
		nresrv = atoi(ARGF());
		break;
	case 't':
		type = ARGF();
		break;
	case 'v':
		chatty++;
		break;
	case 'x':
		xflag = 1;
		break;
	default:
		usage();
	} ARGEND

	if(argc < 1)
		usage();

	disk = opendisk(argv[0], 0, 0);
	if(disk == nil) {
		if(fflag) {
			if((fd = create(argv[0], ORDWR, 0666)) >= 0) {
				file = argv[0];
				close(fd);
				disk = opendisk(argv[0], 0, 0);
			}
		}
	}
	if(disk == nil)
		fatal("opendisk: %r");

	if(disk->type == Tfile)
		fflag = 1;

	if(type == nil) {
		switch(disk->type){
		case Tfile:
			type = "3½HD";
			break;
		case Tfloppy:
			seek(disk->ctlfd, 0, 0);
			n = read(disk->ctlfd, buf, 10);
			if(n <= 0 || n >= 10)
				fatal("reading floppy type");
			buf[n] = 0;
			type = strdup(buf);
			if(type == nil)
				fatal("out of memory");
			break;
		case Tsd:
			type = "hard";
			break;
		default:
			type = "unknown";
			break;
		}
	}

	if(!fflag && disk->type == Tfloppy)
		if(fprint(disk->ctlfd, "format %s", type) < 0)
			fatal("formatting floppy as %s: %r", type);

	if(disk->type != Tfloppy)
		sanitycheck(disk);

	/* check that everything will succeed */
	dosfs(dos, writepbs, disk, label, argc-1, argv+1, 0);

	/* commit */
	dosfs(dos, writepbs, disk, label, argc-1, argv+1, 1);

	print("used %lld bytes\n", fatlast*clustersize*disk->secsize);
	exits(0);
}

/*
 * Look for a partition table on sector 1, as would be the
 * case if we were erroneously formatting 9fat without -r 2.
 * If it's there and nresrv is not big enough, complain and exit.
 * I've blown away my partition table too many times.
 */
void
sanitycheck(Disk *disk)
{
	char buf[512];
	int bad;

	if(xflag)
		return;

	bad = 0;
	if(dos && nresrv < 2 && seek(disk->fd, disk->secsize, 0) == disk->secsize
	&& read(disk->fd, buf, sizeof(buf)) >= 5 && strncmp(buf, "part ", 5) == 0) {
		fprint(2, 
			"there's a plan9 partition on the disk\n"
			"and you didn't specify -r 2 (or greater).\n"
			"either specify -r 2 or -x to disable this check.\n");
		bad = 1;
	}

	if(disk->type == Tsd && disk->offset == 0LL) {
		fprint(2,
			"you're attempting to format your disk (/dev/sdXX/data)\n"
			"rather than a partition like /dev/sdXX/9fat;\n"
			"this is likely a mistake.  specify -x to disable this check.\n");
		bad = 1;
	}

	if(bad)
		exits("failed disk sanity check");
}

/*
 * Return the BIOS drive number for the disk.
 * 0x80 is the first fixed disk, 0x81 the next, etc.
 * We map sdC0=0x80, sdC1=0x81, sdD0=0x82, sdD1=0x83
 */
int
getdriveno(Disk *disk)
{
	char buf[64], *p;

	if(disk->type != Tsd)
		return 0x80;	/* first hard disk */

	if(fd2path(disk->fd, buf, sizeof(buf)) < 0)
		return 0x80;

	/*
	 * The name is of the format #SsdC0/foo 
	 * or /dev/sdC0/foo.
	 * So that we can just look for /sdC0, turn 
	 * #SsdC0/foo into #/sdC0/foo.
	 */
	if(buf[0] == '#' && buf[1] == 'S')
		buf[1] = '/';

	for(p=buf; *p; p++)
		if(p[0] == 's' && p[1] == 'd' && (p[2]=='C' || p[2]=='D') && (p[3]=='0' || p[3]=='1'))
			return 0x80 + (p[2]-'C')*2 + (p[3]-'0');
		
	return 0x80;
}

long
writen(int fd, void *buf, long n)
{
	/* write 8k at a time, to be nice to the disk subsystem */
	
	long m, tot;

	for(tot=0; tot<n; tot+=m){
		m = n - tot;
		if(m > 8192)
			m = 8192;
		if(write(fd, (uchar*)buf+tot, m) != m)
			break;
	}
	return tot;
}

void
dosfs(int dofat, int dopbs, Disk *disk, char *label, int argc, char *argv[], int commit)
{
	char r[16];
	Dosboot *b;
	uchar *buf, *pbsbuf, *p;
	Dir *d;
	int i, data, newclusters, npbs, n, sysfd;
	ulong x;
	vlong length;
	vlong secsize;

	if(dofat == 0 && dopbs == 0)
		return;

	for(t = floppytype; t < &floppytype[NTYPES]; t++)
		if(strcmp(type, t->name) == 0)
			break;
	if(t == &floppytype[NTYPES])
		fatal("unknown floppy type %s", type);

	if(t->sectors == 0 && strcmp(type, "hard") == 0) {
		t->sectors = disk->s;
		t->heads = disk->h;
		t->tracks = disk->c;
	}

	if(t->sectors == 0 && dofat)
		fatal("cannot format fat with type %s: geometry unknown\n", type);

	if(fflag){
		disk->size = t->bytes*t->sectors*t->heads*t->tracks;
		disk->secsize = t->bytes;
		disk->secs = disk->size / disk->secsize;