buf_subs.c

早期freebsd实现

/*-
 * Copyright (c) 1992 Keith Muller.
 * Copyright (c) 1992, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Keith Muller of the University of California, San Diego.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#ifndef lint
static char sccsid[] = "@(#)buf_subs.c	8.2 (Berkeley) 4/18/94";
#endif /* not lint */

#include <sys/types.h>
#include <sys/time.h>
#include <sys/stat.h>
#include <sys/param.h>
#include <stdio.h>
#include <ctype.h>
#include <errno.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include "pax.h"
#include "extern.h"

/*
 * routines which implement archive and file buffering
 */

#define MINFBSZ		512		/* default block size for hole detect */
#define MAXFLT          10              /* default media read error limit */

/*
 * Need to change bufmem to dynamic allocation when the upper
 * limit on blocking size is removed (though that will violate pax spec)
 * MAXBLK define and tests will also need to be updated.
 */
static char bufmem[MAXBLK+BLKMULT];	/* i/o buffer + pushback id space */
static char *buf;			/* normal start of i/o buffer */
static char *bufend;			/* end or last char in i/o buffer */
static char *bufpt;			/* read/write point in i/o buffer */
int blksz = MAXBLK;                    	/* block input/output size in bytes */
int wrblksz;                      	/* user spec output size in bytes */
int maxflt = MAXFLT;			/* MAX consecutive media errors */
int rdblksz;				/* first read blksize (tapes only) */
off_t wrlimit;				/* # of bytes written per archive vol */
off_t wrcnt;				/* # of bytes written on current vol */
off_t rdcnt;				/* # of bytes read on current vol */

/*
 * wr_start()
 *	set up the buffering system to operate in a write mode
 * Return:
 *	0 if ok, -1 if the user specified write block size violates pax spec
 */

#if __STDC__
int
wr_start(void)
#else
int
wr_start()
#endif
{
	buf = &(bufmem[BLKMULT]);
	/*
	 * Check to make sure the write block size meets pax specs. If the user
	 * does not specify a blocksize, we use the format default blocksize.
	 * We must be picky on writes, so we do not allow the user to create an
	 * archive that might be hard to read elsewhere. If all ok, we then
	 * open the first archive volume
	 */
	if (!wrblksz)  
		wrblksz = frmt->bsz;
	if (wrblksz > MAXBLK) {
		warn(1, "Write block size of %d too large, maximium is: %d",
			wrblksz, MAXBLK);
		return(-1);
	}
	if (wrblksz % BLKMULT) {
		warn(1, "Write block size of %d is not a %d byte multiple",
		    wrblksz, BLKMULT);
		return(-1);
	}

	/*
	 * we only allow wrblksz to be used with all archive operations 
	 */
	blksz = rdblksz = wrblksz;
	if ((ar_open(arcname) < 0) && (ar_next() < 0))
		return(-1);
	wrcnt = 0;
	bufend = buf + wrblksz;
	bufpt = buf;
	return(0);
}

/*
 * rd_start()
 *	set up buffering system to read an archive
 * Return:
 *	0 if ok, -1 otherwise
 */

#if __STDC__
int
rd_start(void)
#else
int
rd_start()
#endif
{
	/*
	 * leave space for the header pushback (see get_arc()). If we are
	 * going to append and user specified a write block size, check it
	 * right away
	 */
	buf = &(bufmem[BLKMULT]);
	if ((act == APPND) && wrblksz) {
		if (wrblksz > MAXBLK) {
			warn(1,"Write block size %d too large, maximium is: %d",
				wrblksz, MAXBLK);
			return(-1);
		}
		if (wrblksz % BLKMULT) {
			warn(1, "Write block size %d is not a %d byte multiple",
		    	wrblksz, BLKMULT);
			return(-1);
		}
	}

	/*
	 * open the archive
	 */
	if ((ar_open(arcname) < 0) && (ar_next() < 0))
		return(-1);
	bufend = buf + rdblksz;
	bufpt = bufend;
	rdcnt = 0;
	return(0);
}

/*
 * cp_start()
 *	set up buffer system for copying within the file system
 */

#if __STDC__
void
cp_start(void)
#else
void
cp_start()
#endif
{
	buf = &(bufmem[BLKMULT]);
	rdblksz = blksz = MAXBLK;
}

/*
 * appnd_start()
 *	Set up the buffering system to append new members to an archive that
 *	was just read. The last block(s) of an archive may contain a format
 *	specific trailer. To append a new member, this trailer has to be
 *	removed from the archive. The first byte of the trailer is replaced by
 *	the start of the header of the first file added to the archive. The
 *	format specific end read function tells us how many bytes to move
 *	backwards in the archive to be positioned BEFORE the trailer. Two
 *	different postions have to be adjusted, the O.S. file offset (e.g. the
 *	position of the tape head) and the write point within the data we have
 *	stored in the read (soon to become write) buffer. We may have to move
 *	back several records (the number depends on the size of the archive
 *	record and the size of the format trailer) to read up the record where
 *	the first byte of the trailer is recorded. Trailers may span (and
 *	overlap) record boundries.
 *	We first calculate which record has the first byte of the trailer. We
 *	move the OS file offset back to the start of this record and read it
 *	up. We set the buffer write pointer to be at this byte (the byte where
 *	the trailer starts). We then move the OS file pointer back to the
 *	start of this record so a flush of this buffer will replace the record
 *	in the archive.
 *	A major problem is rewriting this last record. For archives stored
 *	on disk files, this is trival. However, many devices are really picky
 *	about the conditions under which they will allow a write to occur.
 *	Often devices restrict the conditions where writes can be made writes,
 *	so it may not be feasable to append archives stored on all types of
 *	devices. 
 * Return:
 *	0 for success, -1 for failure
 */

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

	if (exit_val != 0) {
		warn(0, "Cannot append to an archive that may have flaws.");
		return(-1);
	}
	/*
	 * if the user did not specify a write blocksize, inherit the size used
	 * in the last archive volume read. (If a is set we still use rdblksz
	 * until next volume, cannot shift sizes within a single volume).
	 */
	if (!wrblksz)
		wrblksz = blksz = rdblksz;
	else
		blksz = rdblksz;

	/*
	 * make sure that this volume allows appends
	 */
	if (ar_app_ok() < 0)
		return(-1);

	/*
	 * Calculate bytes to move back and move in front of record where we
	 * need to start writing from. Remember we have to add in any padding
	 * that might be in the buffer after the trailer in the last block. We
	 * travel skcnt + padding ROUNDED UP to blksize.
	 */
	skcnt += bufend - bufpt;
	if ((cnt = (skcnt/blksz) * blksz) < skcnt)
		cnt += blksz;
	if (ar_rev((off_t)cnt) < 0)
		goto out;

	/*
	 * We may have gone too far if there is valid data in the block we are
	 * now in front of, read up the block and position the pointer after
	 * the valid data.
	 */
	if ((cnt -= skcnt) > 0) {
		/*
		 * watch out for stupid tape drives. ar_rev() will set rdblksz
		 * to be real physical blocksize so we must loop until we get
		 * the old rdblksz (now in blksz). If ar_rev() fouls up the
		 * determination of the physical block size, we will fail.
		 */
		bufpt = buf;
		bufend = buf + blksz;
		while (bufpt < bufend) {
			if ((res = ar_read(bufpt, rdblksz)) <= 0)
				goto out;
			bufpt += res;
		}
		if (ar_rev((off_t)(bufpt - buf)) < 0)
			goto out;
		bufpt = buf + cnt;
		bufend = buf + blksz;
	} else {
		/*
		 * buffer is empty
		 */
		bufend = buf + blksz;
		bufpt = buf;
	}
	rdblksz = blksz;
	rdcnt -= skcnt;
	wrcnt = 0;

	/*
	 * At this point we are ready to write. If the device requires special
	 * handling to write at a point were previously recorded data resides,
	 * that is handled in ar_set_wr(). From now on we operate under normal
	 * ARCHIVE mode (write) conditions
	 */
	if (ar_set_wr() < 0)
		return(-1);
	act = ARCHIVE;
	return(0);

    out:
	warn(1, "Unable to rewrite archive trailer, cannot append.");
	return(-1);
}
	
/*
 * rd_sync()
 *	A read error occurred on this archive volume. Resync the buffer and
 *	try to reset the device (if possible) so we can continue to read. Keep
 *	trying to do this until we get a valid read, or we reach the limit on
 *	consecutive read faults (at which point we give up). The user can
 *	adjust the read error limit through a command line option.
 * Returns:
 *	0 on success, and -1 on failure
 */

#if __STDC__
int
rd_sync(void)
#else
int
rd_sync()
#endif
{
	register int errcnt = 0;
	register int res;

	/*
	 * if the user says bail out on first fault, we are out of here...
	 */
	if (maxflt == 0)
		return(-1);
	if (act == APPND) {
		warn(1, "Unable to append when there are archive read errors.");
		return(-1);
	}

	/*
	 * poke at device and try to get past media error
	 */
	if (ar_rdsync() < 0) {
		if (ar_next() < 0)
			return(-1);
		else
			rdcnt = 0;
	}

	for (;;) {
		if ((res = ar_read(buf, blksz)) > 0) {
			/*
			 * All right! got some data, fill that buffer
			 */
			bufpt = buf;
			bufend = buf + res;
			rdcnt += res;
			return(0);
		}

		/*
		 * Oh well, yet another failed read...
		 * if error limit reached, ditch. o.w. poke device to move past
		 * bad media and try again. if media is badly damaged, we ask
		 * the poor (and upset user at this point) for the next archive
		 * volume. remember the goal on reads is to get the most we
		 * can extract out of the archive.
		 */
		if ((maxflt > 0) && (++errcnt > maxflt))
			warn(0,"Archive read error limit (%d) reached",maxflt);
		else if (ar_rdsync() == 0)
			continue;
		if (ar_next() < 0)
			break;
		rdcnt = 0;
		errcnt = 0;
	}
	return(-1);
}

/*
 * pback()
 *	push the data used during the archive id phase back into the I/O
 *	buffer. This is required as we cannot be sure that the header does NOT
 *	overlap a block boundry (as in the case we are trying to recover a
 *	flawed archived). This was not designed to be used for any other
 *	purpose. (What software engineering, HA!)
 *	WARNING: do not even THINK of pback greater than BLKMULT, unless the
 *	pback space is increased.
 */

#if __STDC__
void
pback(char *pt, int cnt)
#else
void
pback(pt, cnt)
	char *pt;
	int cnt;
#endif
{
	bufpt -= cnt;
	bcopy(pt, bufpt, cnt);
	return;
}

/*
 * rd_skip()
 *	skip foward in the archive during a archive read. Used to get quickly
 *	past file data and padding for files the user did NOT select.
 * Return:
 *	0 if ok, -1 failure, and 1 when EOF on the archive volume was detected.
 */

#if __STDC__
int
rd_skip(off_t skcnt)
#else
int
rd_skip(skcnt)
	off_t skcnt;
#endif
{
	off_t res;
	off_t cnt;
	off_t skipped = 0;

	/*
	 * consume what data we have in the buffer. If we have to move foward
	 * whole records, we call the low level skip function to see if we can
	 * move within the archive without doing the expensive reads on data we
	 * do not want.
	 */
	if (skcnt == 0)
		return(0);
	res = MIN((bufend - bufpt), skcnt);
	bufpt += res;
	skcnt -= res;

	/*
	 * if skcnt is now 0, then no additional i/o is needed
	 */
	if (skcnt == 0)
		return(0);

	/*
	 * We have to read more, calculate complete and partial record reads
	 * based on rdblksz. we skip over "cnt" complete records
	 */
	res = skcnt%rdblksz;
	cnt = (skcnt/rdblksz) * rdblksz;

	/*
	 * if the skip fails, we will have to resync. ar_fow will tell us
	 * how much it can skip over. We will have to read the rest.
	 */
	if (ar_fow(cnt, &skipped) < 0)
		return(-1);
	res += cnt - skipped;
	rdcnt += skipped;

	/*
	 * what is left we have to read (which may be the whole thing if
	 * ar_fow() told us the device can only read to skip records);
	 */
	while (res > 0L) {
		cnt = bufend - bufpt;
		/*
		 * if the read fails, we will have to resync
		 */
		if ((cnt <= 0) && ((cnt = buf_fill()) < 0))
			return(-1);
		if (cnt == 0)
			return(1);
		cnt = MIN(cnt, res);
		bufpt += cnt;
		res -= cnt;
	}
	return(0);
}

/* 
 * wr_fin()
 *	flush out any data (and pad if required) the last block. We always pad
 *	with zero (even though we do not have to). Padding with 0 makes it a
 *	lot easier to recover if the archive is damaged. zero paddding SHOULD
 *	BE a requirement....
 */

#if __STDC__
void
wr_fin(void)
#else
void
wr_fin()
#endif
{
	if (bufpt > buf) {
		bzero(bufpt, bufend - bufpt);
		bufpt = bufend;
		(void)buf_flush(blksz);
	}
}

/*
 * wr_rdbuf()
 *	fill the write buffer from data passed to it in a buffer (usually used
 *	by format specific write routines to pass a file header). On failure we
 *	punt. We do not allow the user to continue to write flawed archives.
 *	We assume these headers are not very large (the memory copy we use is
 *	a bit expensive). 
 * Return:
 *	0 if buffer was filled ok, -1 o.w. (buffer flush failure)
 */

#if __STDC__
int
wr_rdbuf(register char *out, register int outcnt)
#else
int
wr_rdbuf(out, outcnt)
	register char *out;
	register int outcnt;
#endif
{
	register int cnt;

	/*
	 * while there is data to copy copy into the write buffer. when the
	 * write buffer fills, flush it to the archive and continue
	 */
	while (outcnt > 0) {
		cnt = bufend - bufpt;
		if ((cnt <= 0) && ((cnt = buf_flush(blksz)) < 0))
			return(-1);