buf_subs.c

早期freebsd实现

		/*
		 * only move what we have space for
		 */
		cnt = MIN(cnt, outcnt);
		bcopy(out, bufpt, cnt);
		bufpt += cnt;
		out += cnt;
		outcnt -= cnt;
	}
	return(0);
}

/*
 * rd_wrbuf()
 *	copy from the read buffer into a supplied buffer a specified number of
 *	bytes. If the read buffer is empty fill it and continue to copy.
 *	usually used to obtain a file header for processing by a format
 *	specific read routine.
 * Return
 *	number of bytes copied to the buffer, 0 indicates EOF on archive volume,
 *	-1 is a read error
 */

#if __STDC__
int
rd_wrbuf(register char *in, register int cpcnt)
#else
int
rd_wrbuf(in, cpcnt)
	register char *in;
	register int cpcnt;
#endif
{
	register int res;
	register int cnt;
	register int incnt = cpcnt;

	/*
	 * loop until we fill the buffer with the requested number of bytes
	 */
	while (incnt > 0) {
		cnt = bufend - bufpt;
		if ((cnt <= 0) && ((cnt = buf_fill()) <= 0)) {
			/*
			 * read error, return what we got (or the error if
			 * no data was copied). The caller must know that an
			 * error occured and has the best knowledge what to
			 * do with it
			 */
			if ((res = cpcnt - incnt) > 0)
				return(res);
			return(cnt);
		}

		/*
		 * calculate how much data to copy based on whats left and
		 * state of buffer
		 */
		cnt = MIN(cnt, incnt);
		bcopy(bufpt, in, cnt);
		bufpt += cnt;
		incnt -= cnt;
		in += cnt;
	}
	return(cpcnt);
}

/*
 * wr_skip()
 *	skip foward during a write. In other words add padding to the file.
 *	we add zero filled padding as it makes flawed archives much easier to
 *	recover from. the caller tells us how many bytes of padding to add
 *	This routine was not designed to add HUGE amount of padding, just small
 *	amounts (a few 512 byte blocks at most)
 * Return:
 *	0 if ok, -1 if there was a buf_flush failure
 */

#if __STDC__
int
wr_skip(off_t skcnt)
#else
int
wr_skip(skcnt)
	off_t skcnt;
#endif
{
	register int cnt;

	/*
	 * loop while there is more padding to add
	 */
	while (skcnt > 0L) {
		cnt = bufend - bufpt;
		if ((cnt <= 0) && ((cnt = buf_flush(blksz)) < 0))
			return(-1);
		cnt = MIN(cnt, skcnt);
		bzero(bufpt, cnt);
		bufpt += cnt;
		skcnt -= cnt;
	}
	return(0);
}

/*
 * wr_rdfile()
 *	fill write buffer with the contents of a file. We are passed an	open
 *	file descriptor to the file an the archive structure that describes the
 *	file we are storing. The variable "left" is modified to contain the
 *	number of bytes of the file we were NOT able to write to the archive.
 *	it is important that we always write EXACTLY the number of bytes that
 *	the format specific write routine told us to. The file can also get
 *	bigger, so reading to the end of file would create an improper archive,
 *	we just detect this case and warn the user. We never create a bad
 *	archive if we can avoid it. Of course trying to archive files that are
 *	active is asking for trouble. It we fail, we pass back how much we
 *	could NOT copy and let the caller deal with it.
 * Return:
 *	0 ok, -1 if archive write failure. a short read of the file returns a
 *	0, but "left" is set to be greater than zero.
 */

#if __STDC__
int
wr_rdfile(ARCHD *arcn, int ifd, off_t *left)
#else
int
wr_rdfile(arcn, ifd, left)
	ARCHD *arcn;
	int ifd;
	off_t *left;
#endif
{
	register int cnt;
	register int res = 0;
	register off_t size = arcn->sb.st_size;
	struct stat sb;

	/*
	 * while there are more bytes to write
	 */
	while (size > 0L) {
		cnt = bufend - bufpt;
		if ((cnt <= 0) && ((cnt = buf_flush(blksz)) < 0)) {
			*left = size;
			return(-1);
		}
		cnt = MIN(cnt, size);
		if ((res = read(ifd, bufpt, cnt)) <= 0)
			break;
		size -= res;
		bufpt += res;
	}

	/*
	 * better check the file did not change during this operation
	 * or the file read failed.
	 */
	if (res < 0)
		syswarn(1, errno, "Read fault on %s", arcn->org_name);
	else if (size != 0L)
		warn(1, "File changed size during read %s", arcn->org_name);
	else if (fstat(ifd, &sb) < 0)
		syswarn(1, errno, "Failed stat on %s", arcn->org_name);
	else if (arcn->sb.st_mtime != sb.st_mtime)
		warn(1, "File %s was modified during copy to archive",
			arcn->org_name);
	*left = size;
	return(0);
}

/*
 * rd_wrfile()
 *	extract the contents of a file from the archive. If we are unable to
 *	extract the entire file (due to failure to write the file) we return
 *	the numbers of bytes we did NOT process. This way the caller knows how
 *	many bytes to skip past to find the next archive header. If the failure
 *	was due to an archive read, we will catch that when we try to skip. If
 *	the format supplies a file data crc value, we calculate the actual crc
 *	so that it can be compared to the value stored in the header
 * NOTE:
 *	We call a special function to write the file. This function attempts to
 *	restore file holes (blocks of zeros) into the file. When files are
 *	sparse this saves space, and is a LOT faster. For non sparse files
 *	the performance hit is small. As of this writing, no archive supports
 *	information on where the file holes are.
 * Return:
 *	0 ok, -1 if archive read failure. if we cannot write the entire file,
 *	we return a 0 but "left" is set to be the amount unwritten
 */

#if __STDC__
int
rd_wrfile(ARCHD *arcn, int ofd, off_t *left)
#else
int
rd_wrfile(arcn, ofd, left)
	ARCHD *arcn;
	int ofd;
	off_t *left;
#endif
{
	register int cnt = 0;
	register off_t size = arcn->sb.st_size;
	register int res = 0;
	register char *fnm = arcn->name;
	int isem = 1;
	int rem;
	int sz = MINFBSZ;
 	struct stat sb;
	u_long crc = 0L;

	/*
	 * pass the blocksize of the file being written to the write routine,
	 * if the size is zero, use the default MINFBSZ
	 */
        if (fstat(ofd, &sb) == 0) {
		if (sb.st_blksize > 0)
			sz = (int)sb.st_blksize;
        } else
                syswarn(0,errno,"Unable to obtain block size for file %s",fnm);
	rem = sz;
	*left = 0L;

	/*
	 * Copy the archive to the file the number of bytes specified. We have
	 * to assume that we want to recover file holes as none of the archive
	 * formats can record the location of file holes.
	 */
	while (size > 0L) {
		cnt = bufend - bufpt;
		/*
		 * if we get a read error, we do not want to skip, as we may
		 * miss a header, so we do not set left, but if we get a write
		 * error, we do want to skip over the unprocessed data.
		 */
		if ((cnt <= 0) && ((cnt = buf_fill()) <= 0))
			break;
		cnt = MIN(cnt, size);
		if ((res = file_write(ofd,bufpt,cnt,&rem,&isem,sz,fnm)) <= 0) {
			*left = size;
			break;
		}

		if (docrc) {
			/*
			 * update the actual crc value
			 */
			cnt = res;
			while (--cnt >= 0)
				crc += *bufpt++ & 0xff;
		} else
			bufpt += res;
		size -= res;
	}

	/*
	 * if the last block has a file hole (all zero), we must make sure this
	 * gets updated in the file. We force the last block of zeros to be
	 * written. just closing with the file offset moved foward may not put
	 * a hole at the end of the file.
	 */
	if (isem && (arcn->sb.st_size > 0L))
		file_flush(ofd, fnm, isem);

	/*
	 * if we failed from archive read, we do not want to skip
	 */
	if ((size > 0L) && (*left == 0L)) 
		return(-1);

	/*
	 * some formats record a crc on file data. If so, then we compare the
	 * calculated crc to the crc stored in the archive
	 */
	if (docrc && (size == 0L) && (arcn->crc != crc))
		warn(1,"Actual crc does not match expected crc %s",arcn->name);
	return(0);
}

/*
 * cp_file()
 *	copy the contents of one file to another. used during -rw phase of pax
 *	just as in rd_wrfile() we use a special write function to write the
 *	destination file so we can properly copy files with holes.
 */

#if __STDC__
void
cp_file(ARCHD *arcn, int fd1, int fd2)
#else
void
cp_file(arcn, fd1, fd2)
	ARCHD *arcn;
	int fd1;
	int fd2;
#endif
{
	register int cnt;
	register off_t cpcnt = 0L;
	register int res = 0;
	register char *fnm = arcn->name;
	register int no_hole = 0;
	int isem = 1;
	int rem;
	int sz = MINFBSZ;
	struct stat sb;

	/*
	 * check for holes in the source file. If none, we will use regular
	 * write instead of file write.
	 */
	 if (((off_t)(arcn->sb.st_blocks * BLKMULT)) >= arcn->sb.st_size)
		++no_hole;

	/*
	 * pass the blocksize of the file being written to the write routine,
	 * if the size is zero, use the default MINFBSZ
	 */
        if (fstat(fd2, &sb) == 0) {
		if (sb.st_blksize > 0)
			sz = sb.st_blksize;
        } else
                syswarn(0,errno,"Unable to obtain block size for file %s",fnm);
	rem = sz;

	/*
	 * read the source file and copy to destination file until EOF
	 */
	for(;;) {
		if ((cnt = read(fd1, buf, blksz)) <= 0)
			break;
		if (no_hole)
			res = write(fd2, buf, cnt);
		else
			res = file_write(fd2, buf, cnt, &rem, &isem, sz, fnm);
		if (res != cnt)
			break;
		cpcnt += cnt;
	}

	/*
	 * check to make sure the copy is valid.
	 */
	if (res < 0)
		syswarn(1, errno, "Failed write during copy of %s to %s",
			arcn->org_name, arcn->name);
	else if (cpcnt != arcn->sb.st_size)
		warn(1, "File %s changed size during copy to %s",
			arcn->org_name, arcn->name);
	else if (fstat(fd1, &sb) < 0)
		syswarn(1, errno, "Failed stat of %s", arcn->org_name);
	else if (arcn->sb.st_mtime != sb.st_mtime)
		warn(1, "File %s was modified during copy to %s",
			arcn->org_name, arcn->name);

	/*
	 * if the last block has a file hole (all zero), we must make sure this
	 * gets updated in the file. We force the last block of zeros to be
	 * written. just closing with the file offset moved foward may not put
	 * a hole at the end of the file.
	 */
	if (!no_hole && isem && (arcn->sb.st_size > 0L))
		file_flush(fd2, fnm, isem);
	return;
}

/*
 * buf_fill()
 *	fill the read buffer with the next record (or what we can get) from
 *	the archive volume.
 * Return:
 *	Number of bytes of data in the read buffer, -1 for read error, and
 *	0 when finished (user specified termination in ar_next()).
 */

#if __STDC__
int
buf_fill(void)
#else
int
buf_fill()
#endif
{
	register int cnt;
	static int fini = 0;

	if (fini)
		return(0);

	for(;;) {
		/*
		 * try to fill the buffer. on error the next archive volume is
		 * opened and we try again.
		 */
		if ((cnt = ar_read(buf, blksz)) > 0) {
			bufpt = buf;
			bufend = buf + cnt;
			rdcnt += cnt;
			return(cnt);
		}

		/*
		 * errors require resync, EOF goes to next archive
		 */
		if (cnt < 0)
			break;
		if (ar_next() < 0) {
			fini = 1;
			return(0);
		}
		rdcnt = 0;
	}
	exit_val = 1;
	return(-1);
}

/*
 * buf_flush()
 *	force the write buffer to the archive. We are passed the number of
 *	bytes in the buffer at the point of the flush. When we change archives
 *	the record size might change. (either larger or smaller).
 * Return:
 *	0 if all is ok, -1 when a write error occurs.
 */

#if __STDC__
int
buf_flush(register int bufcnt)
#else
int
buf_flush(bufcnt)
	register int bufcnt;
#endif
{
	register int cnt;
	register int push = 0;
	register int totcnt = 0;

	/*
	 * if we have reached the user specified byte count for each archive
	 * volume, prompt for the next volume. (The non-standrad -R flag).
	 * NOTE: If the wrlimit is smaller than wrcnt, we will always write
	 * at least one record. We always round limit UP to next blocksize.
	 */
	if ((wrlimit > 0) && (wrcnt > wrlimit)) {
		warn(0, "User specified archive volume byte limit reached.");
		if (ar_next() < 0) {
			wrcnt = 0;
			exit_val = 1;
			return(-1);
		}
		wrcnt = 0;

		/*
		 * The new archive volume might have changed the size of the
		 * write blocksize. if so we figure out if we need to write
		 * (one or more times), or if there is now free space left in
		 * the buffer (it is no longer full). bufcnt has the number of
		 * bytes in the buffer, (the blocksize, at the point we were
		 * CALLED). Push has the amount of "extra" data in the buffer
		 * if the block size has shrunk from a volume change.
		 */
		bufend = buf + blksz;
		if (blksz > bufcnt)
			return(0);
		if (blksz < bufcnt)
			push = bufcnt - blksz;
	}

	/*
	 * We have enough data to write at least one archive block
	 */
	for (;;) {
		/*
		 * write a block and check if it all went out ok
		 */
		cnt = ar_write(buf, blksz); 
		if (cnt == blksz) {
			/*
			 * the write went ok
			 */
			wrcnt += cnt;
			totcnt += cnt;
			if (push > 0) {
				/* we have extra data to push to the front.
				 * check for more than 1 block of push, and if
				 * so we loop back to write again
				 */
				bcopy(bufend, buf, push);
				bufpt = buf + push;
				if (push >= blksz) {
					push -= blksz;
					continue;
				}
			} else
				bufpt = buf;
			return(totcnt);
		} else if (cnt > 0) {
			/*
			 * Oh drat we got a partial write!
			 * if format doesnt care about alignment let it go,
			 * we warned the user in ar_write().... but this means
			 * the last record on this volume violates pax spec....
			 */
			totcnt += cnt;
			wrcnt += cnt;
			bufpt = buf + cnt;
			cnt = bufcnt - cnt;
			bcopy(bufpt, buf, cnt);
			bufpt = buf + cnt;
			if (!frmt->blkalgn || ((cnt % frmt->blkalgn) == 0))
				return(totcnt);
			break;
		}

		/*
		 * All done, go to next archive
		 */
		wrcnt = 0;
		if (ar_next() < 0)
			break;

		/*
		 * The new archive volume might also have changed the block
		 * size. if so, figure out if we have too much or too little
		 * data for using the new block size
		 */
		bufend = buf + blksz;
		if (blksz > bufcnt)
			return(0);
		if (blksz < bufcnt)
			push = bufcnt - blksz;
	}

	/*
	 * write failed, stop pax. we must not create a bad archive!
	 */
	exit_val = 1;
	return(-1);
}