tar.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

		pfxlen = sl - name;
		if (pfxlen <= sizeof hp->prefix && namlen-1 - pfxlen <= Namsiz)
			break;
		osl = sl;
		*osl = '\0';
		sl = strrchr(name, '/');
		*osl = '/';
	}
	if (sl == nil) {
		fprint(2, "%s: name can't be split to fit tar header: %s\n",
			argv0, name);
		return -1;
	}
	*sl = '\0';
	strncpy(hp->prefix, name, sizeof hp->prefix);
	*sl++ = '/';
	strncpy(hp->name, sl, sizeof hp->name);
	if (slname)
		s_free(slname);
	return 0;
}

static int
mkhdr(Hdr *hp, Dir *dir, char *file)
{
	/*
	 * these fields run together, so we format them in order and don't use
	 * snprint.
	 */
	sprint(hp->mode, "%6lo ", dir->mode & 0777);
	sprint(hp->uid, "%6o ", aruid);
	sprint(hp->gid, "%6o ", argid);
	if (dir->length >= (Off)1<<32) {
		static int printed;

		if (!printed) {
			printed = 1;
			fprint(2, "%s: storing large sizes in \"base 256\"\n", argv0);
		}
		hp->size[0] = Binsize;
		/* emit so-called `base 256' representation of size */
		putbe((uchar *)hp->size+1, dir->length, sizeof hp->size - 2);
		hp->size[sizeof hp->size - 1] = ' ';
	} else
		sprint(hp->size, "%11lluo ", dir->length);
	sprint(hp->mtime, "%11luo ", dir->mtime);
	hp->linkflag = (dir->mode&DMDIR? LF_DIR: LF_PLAIN1);
	putfullname(hp, file);
	if (posix) {
		strncpy(hp->magic, "ustar", sizeof hp->magic);
		strncpy(hp->version, "00", sizeof hp->version);
		strncpy(hp->uname, dir->uid, sizeof hp->uname);
		strncpy(hp->gname, dir->gid, sizeof hp->gname);
	}
	sprint(hp->chksum, "%6luo", chksum(hp));
	return 0;
}

static void addtoar(int ar, char *file, char *shortf);

static void
addtreetoar(int ar, char *file, char *shortf, int fd)
{
	int n;
	Dir *dent, *dirents;
	String *name = s_new();

	n = dirreadall(fd, &dirents);
	if (n < 0)
		fprint(2, "%s: dirreadall %s: %r\n", argv0, file);
	close(fd);
	if (n <= 0)
		return;

	if (chdir(shortf) < 0)
		sysfatal("chdir %s: %r", file);
	if (DEBUG)
		fprint(2, "chdir %s\t# %s\n", shortf, file);

	for (dent = dirents; dent < dirents + n; dent++) {
		s_reset(name);
		s_append(name, file);
		s_append(name, "/");
		s_append(name, dent->name);
		addtoar(ar, s_to_c(name), dent->name);
	}
	s_free(name);
	free(dirents);

	/*
	 * this assumes that shortf is just one component, which is true
	 * during directory descent, but not necessarily true of command-line
	 * arguments.  Our caller (or addtoar's) must reset the working
	 * directory if necessary.
	 */
	if (chdir("..") < 0)
		sysfatal("chdir %s/..: %r", file);
	if (DEBUG)
		fprint(2, "chdir ..\n");
}

static void
addtoar(int ar, char *file, char *shortf)
{
	int n, fd, isdir;
	long bytes;
	ulong blksleft, blksread;
	Hdr *hbp;
	Dir *dir;
	String *name = nil;

	if (shortf[0] == '#') {
		name = s_new();
		s_append(name, "./");
		s_append(name, shortf);
		shortf = s_to_c(name);
	}

	fd = open(shortf, OREAD);
	if (fd < 0) {
		fprint(2, "%s: can't open %s: %r\n", argv0, file);
		if (name)
			s_free(name);
		return;
	}
	dir = dirfstat(fd);
	if (dir == nil)
		sysfatal("can't fstat %s: %r", file);

	hbp = getblkz(ar);
	isdir = !!(dir->qid.type&QTDIR);
	if (mkhdr(hbp, dir, file) < 0) {
		putbackblk(ar);
		free(dir);
		close(fd);
		if (name)
			s_free(name);
		return;
	}
	putblk(ar);

	blksleft = BYTES2TBLKS(dir->length);
	free(dir);

	if (isdir)
		addtreetoar(ar, file, shortf, fd);
	else {
		for (; blksleft > 0; blksleft -= blksread) {
			hbp = getblke(ar);
			blksread = gothowmany(blksleft);
			bytes = blksread * Tblock;
			n = readn(fd, hbp->data, bytes);
			if (n < 0)
				sysfatal("error reading %s: %r", file);
			/*
			 * ignore EOF.  zero any partial block to aid
			 * compression and emergency recovery of data.
			 */
			if (n < Tblock)
				memset(hbp->data + n, 0, bytes - n);
			putblkmany(ar, blksread);
		}
		close(fd);
		if (verbose)
			fprint(2, "%s\n", file);
	}
	if (name)
		s_free(name);
}

static char *
replace(char **argv)
{
	int i, ar;
	ulong blksleft, blksread;
	Off bytes;
	Hdr *hp;
	Compress *comp = nil;
	Pushstate ps;

	if (usefile && docreate) {
		ar = create(usefile, OWRITE, 0666);
		if (docompress)
			comp = compmethod(usefile);
	} else if (usefile)
		ar = open(usefile, ORDWR);
	else
		ar = Stdout;
	if (comp)
		ar = push(ar, comp->comp, Output, &ps);
	if (ar < 0)
		sysfatal("can't open archive %s: %r", usefile);

	if (usefile && !docreate) {
		/* skip quickly to the end */
		while ((hp = readhdr(ar)) != nil) {
			bytes = arsize(hp);
			for (blksleft = BYTES2TBLKS(bytes);
			     blksleft > 0 && getblkrd(ar, Justnxthdr) != nil;
			     blksleft -= blksread) {
				blksread = gothowmany(blksleft);
				putreadblks(ar, blksread);
			}
		}
		/*
		 * we have just read the end-of-archive Tblock.
		 * now seek back over the (big) archive block containing it,
		 * and back up curblk ptr over end-of-archive Tblock in memory.
		 */
		if (seek(ar, blkoff, 0) < 0)
			sysfatal("can't seek back over end-of-archive: %r");
		curblk--;
	}

	for (i = 0; argv[i] != nil; i++) {
		addtoar(ar, argv[i], argv[i]);
		chdir(origdir);		/* for correctness & profiling */
	}

	/* write end-of-archive marker */
	getblkz(ar);
	putblk(ar);
	getblkz(ar);
	putlastblk(ar);

	if (comp)
		return pushclose(&ps);
	if (ar > Stderr)
		close(ar);
	return nil;
}

/*
 * tar [xt]
 */

/* is pfx a file-name prefix of name? */
static int
prefix(char *name, char *pfx)
{
	int pfxlen = strlen(pfx);
	char clpfx[Maxname+1];

	if (pfxlen > Maxname)
		return 0;
	strcpy(clpfx, pfx);
	cleanname(clpfx);
	return strncmp(pfx, name, pfxlen) == 0 &&
		(name[pfxlen] == '\0' || name[pfxlen] == '/');
}

static int
match(char *name, char **argv)
{
	int i;
	char clname[Maxname+1];

	if (argv[0] == nil)
		return 1;
	strcpy(clname, name);
	cleanname(clname);
	for (i = 0; argv[i] != nil; i++)
		if (prefix(clname, argv[i]))
			return 1;
	return 0;
}

static void
cantcreate(char *s, int mode)
{
	int len;
	static char *last;

	/*
	 * Always print about files.  Only print about directories
	 * we haven't printed about.  (Assumes archive is ordered
	 * nicely.)
	 */
	if(mode&DMDIR){
		if(last){
			/* already printed this directory */
			if(strcmp(s, last) == 0)
				return;
			/* printed a higher directory, so printed this one */
			len = strlen(s);
			if(memcmp(s, last, len) == 0 && last[len] == '/')
				return;
		}
		/* save */
		free(last);
		last = strdup(s);
	}
	fprint(2, "%s: can't create %s: %r\n", argv0, s);
}

static int
makedir(char *s)
{
	int f;

	if (access(s, AEXIST) == 0)
		return -1;
	f = create(s, OREAD, DMDIR | 0777);
	if (f >= 0)
		close(f);
	else
		cantcreate(s, DMDIR);
	return f;
}

static int
mkpdirs(char *s)
{
	int err;
	char *p;

	p = s;
	err = 0;
	while (!err && (p = strchr(p+1, '/')) != nil) {
		*p = '\0';
		err = (access(s, AEXIST) < 0 && makedir(s) < 0);
		*p = '/';
	}
	return -err;
}

/* Call access but preserve the error string. */
static int
xaccess(char *name, int mode)
{
	char err[ERRMAX];
	int rv;

	err[0] = 0;
	errstr(err, sizeof err);
	rv = access(name, mode);
	errstr(err, sizeof err);
	return rv;
}

/* copy a file from the archive into the filesystem */
/* fname is result of name(), so has two extra bytes at beginning */
static void
extract1(int ar, Hdr *hp, char *fname)
{
	int wrbytes, fd = -1, dir = 0;
	long mtime = strtol(hp->mtime, nil, 8);
	ulong mode = strtoul(hp->mode, nil, 8) & 0777;
	Off bytes = hdrsize(hp);		/* for printing */
	ulong blksread, blksleft = BYTES2TBLKS(arsize(hp));
	Hdr *hbp;

	if (isdir(hp)) {
		mode |= DMDIR|0700;
		dir = 1;
	}
	switch (hp->linkflag) {
	case LF_LINK:
	case LF_SYMLINK1:
	case LF_SYMLINK2:
	case LF_FIFO:
		blksleft = 0;
		break;
	}
	if (relative) {
		if(fname[0] == '/')
			*--fname = '.';
		else if(fname[0] == '#'){
			*--fname = '/';
			*--fname = '.';
		}
	}
	if (verb == Xtract) {
		cleanname(fname);
		switch (hp->linkflag) {
		case LF_LINK:
		case LF_SYMLINK1:
		case LF_SYMLINK2:
			fprint(2, "%s: can't make (sym)link %s\n",
				argv0, fname);
			break;
		case LF_FIFO:
			fprint(2, "%s: can't make fifo %s\n", argv0, fname);
			break;
		default:
			if (!keepexisting || access(fname, AEXIST) < 0) {
				int rw = (dir? OREAD: OWRITE);

				fd = create(fname, rw, mode);
				if (fd < 0) {
					mkpdirs(fname);
					fd = create(fname, rw, mode);
				}
				if (fd < 0 &&
				    (!dir || xaccess(fname, AEXIST) < 0))
				    	cantcreate(fname, mode);
			}
			if (fd >= 0 && verbose)
				fprint(2, "%s\n", fname);
			break;
		}
	} else if (verbose) {
		char *cp = ctime(mtime);

		print("%M %8lld %-12.12s %-4.4s %s\n",
			mode, bytes, cp+4, cp+24, fname);
	} else
		print("%s\n", fname);

	if (blksleft == 0)
		bytes = 0;
	for (; blksleft > 0; blksleft -= blksread) {
		hbp = getblkrd(ar, (fd >= 0? Alldata: Justnxthdr));
		if (hbp == nil)
			sysfatal("unexpected EOF on archive extracting %s",
				fname);
		blksread = gothowmany(blksleft);
		if (blksread <= 0)
			fprint(2, "%s: got %ld blocks reading %s!\n",
				argv0, blksread, fname);
		wrbytes = Tblock*blksread;
		if(wrbytes > bytes)
			wrbytes = bytes;
		if (fd >= 0 && write(fd, hbp->data, wrbytes) != wrbytes)
			sysfatal("write error on %s: %r", fname);
		putreadblks(ar, blksread);
		bytes -= wrbytes;
	}
	if (bytes > 0)
		fprint(2,
		    "%s: %lld bytes uncopied at eof; %s not fully extracted\n",
			argv0, bytes, fname);
	if (fd >= 0) {
		/*
		 * directories should be wstated after we're done
		 * creating files in them.
		 */
		if (settime) {
			Dir nd;

			nulldir(&nd);
			nd.mtime = mtime;
			dirfwstat(fd, &nd);
			if (isustar(hp)) {
				nulldir(&nd);
				nd.gid = hp->gname;
				dirfwstat(fd, &nd);
			}
		}
		close(fd);
	}
}

static void
skip(int ar, Hdr *hp, char *fname)
{
	ulong blksleft, blksread;
	Hdr *hbp;

	for (blksleft = BYTES2TBLKS(arsize(hp)); blksleft > 0;
	     blksleft -= blksread) {
		hbp = getblkrd(ar, Justnxthdr);
		if (hbp == nil)
			sysfatal("unexpected EOF on archive extracting %s",
				fname);
		blksread = gothowmany(blksleft);
		putreadblks(ar, blksread);
	}
}

static char *
extract(char **argv)
{
	int ar;
	char *longname;
	Hdr *hp;
	Compress *comp = nil;
	Pushstate ps;

	if (usefile) {
		ar = open(usefile, OREAD);
		comp = compmethod(usefile);
	} else
		ar = Stdin;
	if (comp)
		ar = push(ar, comp->decomp, Input, &ps);
	if (ar < 0)
		sysfatal("can't open archive %s: %r", usefile);

	while ((hp = readhdr(ar)) != nil) {
		longname = name(hp);
		if (match(longname, argv))
			extract1(ar, hp, longname);
		else
			skip(ar, hp, longname);
	}

	if (comp)
		return pushclose(&ps);
	if (ar > Stderr)
		close(ar);
	return nil;
}

void
main(int argc, char *argv[])
{
	int errflg = 0;
	char *ret = nil;

	fmtinstall('M', dirmodefmt);

	TARGBEGIN {
	case 'c':
		docreate++;
		verb = Replace;
		break;
	case 'f':
		usefile = EARGF(usage());
		break;
	case 'g':
		argid = strtoul(EARGF(usage()), 0, 0);
		break;
	case 'k':
		keepexisting++;
		break;
	case 'm':	/* compatibility */
		settime = 0;
		break;
	case 'p':
		posix++;
		break;
	case 'P':
		posix = 0;
		break;
	case 'r':
		verb = Replace;
		break;
	case 'R':
		relative = 0;
		break;
	case 't':
		verb = Toc;
		break;
	case 'T':
		settime++;
		break;
	case 'u':
		aruid = strtoul(EARGF(usage()), 0, 0);
		break;
	case 'v':
		verbose++;
		break;
	case 'x':
		verb = Xtract;
		break;
	case 'z':
		docompress++;
		break;
	case '-':
		break;
	default:
		fprint(2, "tar: unknown letter %C\n", TARGC());
		errflg++;
		break;
	} TARGEND

	if (argc < 0 || errflg)
		usage();

	initblks();
	switch (verb) {
	case Toc:
	case Xtract:
		ret = extract(argv);
		break;
	case Replace:
		if (getwd(origdir, sizeof origdir) == nil)
			strcpy(origdir, "/tmp");
		ret = replace(argv);
		break;
	default:
		usage();
		break;
	}
	exits(ret);
}