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

/*
 * tar - `tape archiver', actually usable on any medium.
 *	POSIX "ustar" compliant when extracting, and by default when creating.
 *	this tar attempts to read and write multiple Tblock-byte blocks
 *	at once to and from the filesystem, and does not copy blocks
 *	around internally.
 */

#include <u.h>
#include <libc.h>
#include <fcall.h>		/* for %M */
#include <String.h>

/*
 * modified versions of those in libc.h; scans only the first arg for
 * keyletters and options.
 */
#define	TARGBEGIN {\
	(argv0 || (argv0 = *argv)), argv++, argc--;\
	if (argv[0]) {\
		char *_args, *_argt;\
		Rune _argc;\
		_args = &argv[0][0];\
		_argc = 0;\
		while(*_args && (_args += chartorune(&_argc, _args)))\
			switch(_argc)
#define	TARGEND	SET(_argt); USED(_argt);USED(_argc);USED(_args); \
	argc--, argv++; } \
	USED(argv); USED(argc); }
#define	TARGC() (_argc)

#define ROUNDUP(a, b)	(((a) + (b) - 1)/(b))
#define BYTES2TBLKS(bytes) ROUNDUP(bytes, Tblock)

/* read big-endian binary integers; args must be (uchar *) */
#define	G2BEBYTE(x)	(((x)[0]<<8)  |  (x)[1])
#define	G3BEBYTE(x)	(((x)[0]<<16) | ((x)[1]<<8)  |  (x)[2])
#define	G4BEBYTE(x)	(((x)[0]<<24) | ((x)[1]<<16) | ((x)[2]<<8) | (x)[3])
#define	G8BEBYTE(x)	(((vlong)G4BEBYTE(x)<<32) | (u32int)G4BEBYTE((x)+4))

typedef vlong Off;
typedef char *(*Refill)(int ar, char *bufs, int justhdr);

enum { Stdin, Stdout, Stderr };
enum { Rd, Wr };			/* pipe fd-array indices */
enum { Output, Input };
enum { None, Toc, Xtract, Replace };
enum { Alldata, Justnxthdr };
enum {
	Tblock = 512,
	Namsiz = 100,
	Maxpfx = 155,		/* from POSIX */
	Maxname = Namsiz + 1 + Maxpfx,
	Binsize = 0x80,		/* flag in size[0], from gnu: positive binary size */
	Binnegsz = 0xff,	/* flag in size[0]: negative binary size */

	Nblock = 40,		/* maximum blocksize */
	Dblock = 20,		/* default blocksize */
	DEBUG = 0,
};

/* POSIX link flags */
enum {
	LF_PLAIN1 =	'\0',
	LF_PLAIN2 =	'0',
	LF_LINK =	'1',
	LF_SYMLINK1 =	'2',
	LF_SYMLINK2 =	's',		/* 4BSD used this */
	LF_CHR =	'3',
	LF_BLK =	'4',
	LF_DIR =	'5',
	LF_FIFO =	'6',
	LF_CONTIG =	'7',
	/* 'A' - 'Z' are reserved for custom implementations */
};

#define islink(lf)	(isreallink(lf) || issymlink(lf))
#define isreallink(lf)	((lf) == LF_LINK)
#define issymlink(lf)	((lf) == LF_SYMLINK1 || (lf) == LF_SYMLINK2)

typedef union {
	uchar	data[Tblock];
	struct {
		char	name[Namsiz];
		char	mode[8];
		char	uid[8];
		char	gid[8];
		char	size[12];
		char	mtime[12];
		char	chksum[8];
		char	linkflag;
		char	linkname[Namsiz];

		/* rest are defined by POSIX's ustar format; see p1003.2b */
		char	magic[6];	/* "ustar" */
		char	version[2];
		char	uname[32];
		char	gname[32];
		char	devmajor[8];
		char	devminor[8];
		char	prefix[Maxpfx]; /* if non-null, path= prefix "/" name */
	};
} Hdr;

typedef struct {
	char	*comp;
	char	*decomp;
	char	*sfx[4];
} Compress;

static Compress comps[] = {
	"gzip",		"gunzip",	{ ".tar.gz", ".tgz" },	/* default */
	"compress",	"uncompress",	{ ".tar.Z",  ".tz" },
	"bzip2",	"bunzip2",	{ ".tar.bz", ".tbz",
					  ".tar.bz2",".tbz2" },
};

typedef struct {
	int	kid;
	int	fd;	/* original fd */
	int	rfd;	/* replacement fd */
	int	input;
	int	open;
} Pushstate;

#define OTHER(rdwr) (rdwr == Rd? Wr: Rd)

static int debug;
static int verb;
static int posix = 1;
static int docreate;
static int aruid;
static int argid;
static int relative = 1;
static int settime;
static int verbose;
static int docompress;
static int keepexisting;
static Off blkoff;	/* offset of the current archive block (not Tblock) */
static Off nexthdr;

static int nblock = Dblock;
static char *usefile;
static char origdir[Maxname*2];
static Hdr *tpblk, *endblk;
static Hdr *curblk;

static void
usage(void)
{
	fprint(2, "usage: %s {crtx}[PRTfgkmpuvz] [archive] file1 file2...\n",
		argv0);
	exits("usage");
}

/* compression */

static Compress *
compmethod(char *name)
{
	int i, nmlen = strlen(name), sfxlen;
	Compress *cp;

	for (cp = comps; cp < comps + nelem(comps); cp++)
		for (i = 0; i < nelem(cp->sfx) && cp->sfx[i]; i++) {
			sfxlen = strlen(cp->sfx[i]);
			if (nmlen > sfxlen &&
			    strcmp(cp->sfx[i], name + nmlen - sfxlen) == 0)
				return cp;
		}
	return docompress? comps: nil;
}

/*
 * push a filter, cmd, onto fd.  if input, it's an input descriptor.
 * returns a descriptor to replace fd, or -1 on error.
 */
static int
push(int fd, char *cmd, int input, Pushstate *ps)
{
	int nfd, pifds[2];
	String *s;

	ps->open = 0;
	ps->fd = fd;
	ps->input = input;
	if (fd < 0 || pipe(pifds) < 0)
		return -1;
	ps->kid = fork();
	switch (ps->kid) {
	case -1:
		return -1;
	case 0:
		if (input)
			dup(pifds[Wr], Stdout);
		else
			dup(pifds[Rd], Stdin);
		close(pifds[input? Rd: Wr]);
		dup(fd, (input? Stdin: Stdout));
		s = s_new();
		if (cmd[0] != '/')
			s_append(s, "/bin/");
		s_append(s, cmd);
		execl(s_to_c(s), cmd, nil);
		sysfatal("can't exec %s: %r", cmd);
	default:
		nfd = pifds[input? Rd: Wr];
		close(pifds[input? Wr: Rd]);
		break;
	}
	ps->rfd = nfd;
	ps->open = 1;
	return nfd;
}

static char *
pushclose(Pushstate *ps)
{
	Waitmsg *wm;

	if (ps->fd < 0 || ps->rfd < 0 || !ps->open)
		return "not open";
	close(ps->rfd);
	ps->rfd = -1;
	ps->open = 0;
	while ((wm = wait()) != nil && wm->pid != ps->kid)
		continue;
	return wm? wm->msg: nil;
}

/*
 * block-buffer management
 */

static void
initblks(void)
{
	free(tpblk);
	tpblk = malloc(Tblock * nblock);
	assert(tpblk != nil);
	endblk = tpblk + nblock;
}

/*
 * (re)fill block buffers from archive.  `justhdr' means we don't care
 * about the data before the next header block.
 */
static char *
refill(int ar, char *bufs, int justhdr)
{
	int i, n;
	unsigned bytes = Tblock * nblock;
	static int done, first = 1, seekable;

	if (done)
		return nil;

	if (first)
		seekable = seek(ar, 0, 1) >= 0;
	blkoff = seek(ar, 0, 1);		/* note position for `tar r' */
	/* try to size non-pipe input at first read */
	if (first && usefile) {
		n = read(ar, bufs, bytes);
		if (n <= 0)
			sysfatal("error reading archive: %r");
		i = n;
		if (i % Tblock != 0) {
			fprint(2, "%s: archive block size (%d) error\n",
				argv0, i);
			exits("blocksize");
		}
		i /= Tblock;
		if (i != nblock) {
			nblock = i;
			fprint(2, "%s: blocking = %d\n", argv0, nblock);
			endblk = (Hdr *)bufs + nblock;
			bytes = n;
		}
	} else if (justhdr && seekable && nexthdr - seek(ar, 0, 1) >= bytes) {
		/* optimisation for huge archive members on seekable media */
		if (seek(ar, bytes, 1) < 0)
			sysfatal("can't seek on archive: %r");
		n = bytes;
	} else
		n = readn(ar, bufs, bytes);
	first = 0;

	if (n == 0)
		sysfatal("unexpected EOF reading archive");
	else if (n < 0)
		sysfatal("error reading archive: %r");
	else if (n%Tblock != 0)
		sysfatal("partial block read from archive");
	if (n != bytes) {
		done = 1;
		memset(bufs + n, 0, bytes - n);
	}
	return bufs;
}

static Hdr *
getblk(int ar, Refill rfp, int justhdr)
{
	if (curblk == nil || curblk >= endblk) {  /* input block exhausted? */
		if (rfp != nil && (*rfp)(ar, (char *)tpblk, justhdr) == nil)
			return nil;
		curblk = tpblk;
	}
	return curblk++;
}

static Hdr *
getblkrd(int ar, int justhdr)
{
	return getblk(ar, refill, justhdr);
}

static Hdr *
getblke(int ar)
{
	return getblk(ar, nil, Alldata);
}

static Hdr *
getblkz(int ar)
{
	Hdr *hp = getblke(ar);

	if (hp != nil)
		memset(hp->data, 0, Tblock);
	return hp;
}

/*
 * how many block buffers are available, starting at the address
 * just returned by getblk*?
 */
static int
gothowmany(int max)
{
	int n = endblk - (curblk - 1);

	return n > max? max: n;
}

/*
 * indicate that one is done with the last block obtained from getblke
 * and it is now available to be written into the archive.
 */
static void
putlastblk(int ar)
{
	unsigned bytes = Tblock * nblock;

	/* if writing end-of-archive, aid compression (good hygiene too) */
	if (curblk < endblk)
		memset(curblk, 0, (char *)endblk - (char *)curblk);
	if (write(ar, tpblk, bytes) != bytes)
		sysfatal("error writing archive: %r");
}

static void
putblk(int ar)
{
	if (curblk >= endblk)
		putlastblk(ar);
}

static void
putbackblk(int ar)
{
	curblk--;
	USED(ar);
}

static void
putreadblks(int ar, int blks)
{
	curblk += blks - 1;
	USED(ar);
}

static void
putblkmany(int ar, int blks)
{
	curblk += blks - 1;
	putblk(ar);
}

/*
 * common routines
 */

/*
 * modifies hp->chksum but restores it; important for the last block of the
 * old archive when updating with `tar rf archive'
 */
static long
chksum(Hdr *hp)
{
	int n = Tblock;
	long i = 0;
	uchar *cp = hp->data;
	char oldsum[sizeof hp->chksum];

	memmove(oldsum, hp->chksum, sizeof oldsum);
	memset(hp->chksum, ' ', sizeof hp->chksum);
	while (n-- > 0)
		i += *cp++;
	memmove(hp->chksum, oldsum, sizeof oldsum);
	return i;
}

static int
isustar(Hdr *hp)
{
	return strcmp(hp->magic, "ustar") == 0;
}

/*
 * s is at most n bytes long, but need not be NUL-terminated.
 * if shorter than n bytes, all bytes after the first NUL must also
 * be NUL.
 */
static int
strnlen(char *s, int n)
{
	return s[n - 1] != '\0'? n: strlen(s);
}

/* set fullname from header */
static char *
name(Hdr *hp)
{
	int pfxlen, namlen;
	static char fullnamebuf[2 + Maxname + 1];	/* 2 at beginning for ./ on relative names */
	char *fullname;

	fullname = fullnamebuf+2;
	namlen = strnlen(hp->name, sizeof hp->name);
	if (hp->prefix[0] == '\0' || !isustar(hp)) {	/* old-style name? */
		memmove(fullname, hp->name, namlen);
		fullname[namlen] = '\0';
		return fullname;
	}

	/* name is in two pieces */
	pfxlen = strnlen(hp->prefix, sizeof hp->prefix);
	memmove(fullname, hp->prefix, pfxlen);
	fullname[pfxlen] = '/';
	memmove(fullname + pfxlen + 1, hp->name, namlen);
	fullname[pfxlen + 1 + namlen] = '\0';
	return fullname;
}

static int
isdir(Hdr *hp)
{
	/* the mode test is ugly but sometimes necessary */
	return hp->linkflag == LF_DIR ||
		strrchr(name(hp), '\0')[-1] == '/' ||
		(strtoul(hp->mode, nil, 8)&0170000) == 040000;
}

static int
eotar(Hdr *hp)
{
	return name(hp)[0] == '\0';
}

/*
static uvlong
getbe(uchar *src, int size)
{
	uvlong vl = 0;

	while (size-- > 0) {
		vl <<= 8;
		vl |= *src++;
	}
	return vl;
}
 */

static void
putbe(uchar *dest, uvlong vl, int size)
{
	for (dest += size; size-- > 0; vl >>= 8)
		*--dest = vl;
}

/*
 * return the nominal size from the header block, which is not always the
 * size in the archive (the archive size may be zero for some file types
 * regardless of the nominal size).
 *
 * gnu and freebsd tars are now recording vlongs as big-endian binary
 * with a flag in byte 0 to indicate this, which permits file sizes up to
 * 2^64-1 (actually 2^80-1 but our file sizes are vlongs) rather than 2^33-1.
 */
static Off
hdrsize(Hdr *hp)
{
	uchar *p;

	if((uchar)hp->size[0] == Binnegsz) {
		fprint(2, "%s: %s: negative length, which is insane\n",
			argv0, name(hp));
		return 0;
	} else if((uchar)hp->size[0] == Binsize) {
		p = (uchar *)hp->size + sizeof hp->size - 1 -
			sizeof(vlong);		/* -1 for terminating space */
		return G8BEBYTE(p);
	} else
		return strtoull(hp->size, nil, 8);
}

/*
 * return the number of bytes recorded in the archive.
 */
static Off
arsize(Hdr *hp)
{
	if(isdir(hp) || islink(hp->linkflag))
		return 0;
	return hdrsize(hp);
}

static Hdr *
readhdr(int ar)
{
	long hdrcksum;
	Hdr *hp;

	hp = getblkrd(ar, Alldata);
	if (hp == nil)
		sysfatal("unexpected EOF instead of archive header");
	if (eotar(hp))			/* end-of-archive block? */
		return nil;
	hdrcksum = strtoul(hp->chksum, nil, 8);
	if (chksum(hp) != hdrcksum)
		sysfatal("bad archive header checksum: name %.64s...",
			hp->name);
	nexthdr += Tblock*(1 + BYTES2TBLKS(arsize(hp)));
	return hp;
}

/*
 * tar r[c]
 */

/*
 * if name is longer than Namsiz bytes, try to split it at a slash and fit the
 * pieces into hp->prefix and hp->name.
 */
static int
putfullname(Hdr *hp, char *name)
{
	int namlen, pfxlen;
	char *sl, *osl;
	String *slname = nil;

	if (isdir(hp)) {
		slname = s_new();
		s_append(slname, name);
		s_append(slname, "/");		/* posix requires this */
		name = s_to_c(slname);
	}

	namlen = strlen(name);
	if (namlen <= Namsiz) {
		strncpy(hp->name, name, Namsiz);
		hp->prefix[0] = '\0';		/* ustar paranoia */
		return 0;
	}

	if (!posix || namlen > Maxname) {
		fprint(2, "%s: name too long for tar header: %s\n",
			argv0, name);
		return -1;
	}
	/*
	 * try various splits until one results in pieces that fit into the
	 * appropriate fields of the header.  look for slashes from right
	 * to left, in the hopes of putting the largest part of the name into
	 * hp->prefix, which is larger than hp->name.
	 */
	sl = strrchr(name, '/');
	while (sl != nil) {