ar_io.c

早期freebsd实现

	lstrval = res;
}

/*
 * ar_set_wr()
 *	Set up device right before switching from read to write in an append.
 *	device dependent code (if required) to do this should be added here.
 *	For all archive devices we are already positioned at the place we want
 *	to start writing when this routine is called.
 * Return:
 *	0 if all ready to write, -1 otherwise
 */

#if __STDC__
int
ar_set_wr(void)
#else
int
ar_set_wr()
#endif
{
	off_t cpos;

	/*
	 * we must make sure the trailer is rewritten on append, ar_next()
	 * will stop us if the archive containing the trailer was not written
	 */
	wr_trail = 0;
	
	/* 
	 * Add any device dependent code as required here
	 */
	if (artyp != ISREG)
		return(0);
	/*
	 * Ok we have an archive in a regular file. If we were rewriting a
	 * file, we must get rid of all the stuff after the current offset
	 * (it was not written by pax).
	 */
	if (((cpos = lseek(arfd, (off_t)0L, SEEK_CUR)) < 0) ||
	    (ftruncate(arfd, cpos) < 0)) {
		syswarn(1, errno, "Unable to truncate archive file");
		return(-1);
	}
	return(0);
}

/*
 * ar_app_ok()
 *	check if the last volume in the archive allows appends. We cannot check
 *	this until we are ready to write since there is no spec that says all 
 *	volumes in a single archive have to be of the same type...
 * Return:
 *	0 if we can append, -1 otherwise.
 */

#if __STDC__
int
ar_app_ok(void)
#else
int
ar_app_ok()
#endif
{
	if (artyp == ISPIPE) {
		warn(1, "Cannot append to an archive obtained from a pipe.");
		return(-1);
	}

	if (!invld_rec)
		return(0);
	warn(1,"Cannot append, device record size %d does not support %s spec",
		rdblksz, argv0);
	return(-1);
}

/*
 * ar_read()
 *	read up to a specified number of bytes from the archive into the
 *	supplied buffer. When dealing with tapes we may not always be able to
 *	read what we want.
 * Return:
 *	Number of bytes in buffer. 0 for end of file, -1 for a read error.
 */

#if __STDC__
int
ar_read(register char *buf, register int cnt)
#else
int
ar_read(buf, cnt)
	register char *buf;
	register int cnt;
#endif
{
	register int res = 0;

	/*
	 * if last i/o was in error, no more reads until reset or new volume
	 */
	if (lstrval <= 0)
		return(lstrval);

	/*
	 * how we read must be based on device type
	 */
	switch (artyp) {
	case ISTAPE:
		if ((res = read(arfd, buf, cnt)) > 0) {
			/*
			 * CAUTION: tape systems may not always return the same
			 * sized records so we leave blksz == MAXBLK. The
			 * physical record size that a tape drive supports is
			 * very hard to determine in a uniform and portable
			 * manner.
			 */
			io_ok = 1;
			if (res != rdblksz) {
				/*
				 * Record size changed. If this is happens on
				 * any record after the first, we probably have
				 * a tape drive which has a fixed record size
				 * we are getting multiple records in a single
				 * read). Watch out for record blocking that
				 * violates pax spec (must be a multiple of
				 * BLKMULT).
				 */
				rdblksz = res;
				if (rdblksz % BLKMULT)
					invld_rec = 1;
			}
			return(res);
		}
		break;
	case ISREG:
	case ISBLK:
	case ISCHR:
	case ISPIPE:
	default:
		/*
		 * Files are so easy to deal with. These other things cannot
		 * be trusted at all. So when we are dealing with character
		 * devices and pipes we just take what they have ready for us
		 * and return. Trying to do anything else with them runs the
		 * risk of failure.
		 */
		if ((res = read(arfd, buf, cnt)) > 0) {
			io_ok = 1;
			return(res);
		}
		break;
	}

	/*
	 * We are in trouble at this point, something is broken...
	 */
	lstrval = res;
	if (res < 0)
		syswarn(1, errno, "Failed read on archive volume %d", arvol);
	else
		warn(0, "End of archive volume %d reached", arvol);
	return(res);
} 

/*
 * ar_write()
 *	Write a specified number of bytes in supplied buffer to the archive
 *	device so it appears as a single "block". Deals with errors and tries
 *	to recover when faced with short writes.
 * Return:
 *	Number of bytes written. 0 indicates end of volume reached and with no
 *	flaws (as best that can be detected). A -1 indicates an unrecoverable
 *	error in the archive occured.
 */

#if __STDC__
int
ar_write(register char *buf, register int bsz)
#else
int
ar_write(buf, bsz)
	register char *buf;
	register int bsz;
#endif
{
	register int res;
	off_t cpos;

	/*
	 * do not allow pax to create a "bad" archive. Once a write fails on
	 * an archive volume prevent further writes to it.
	 */
	if (lstrval <= 0)
		return(lstrval);

	if ((res = write(arfd, buf, bsz)) == bsz) {
		wr_trail = 1;
		io_ok = 1;
		return(bsz);
	}
	/*
	 * write broke, see what we can do with it. We try to send any partial
	 * writes that may violate pax spec to the next archive volume.
	 */
	if (res < 0)
		lstrval = res;
	else
		lstrval = 0;

	switch (artyp) {
	case ISREG:
		if ((res > 0) && (res % BLKMULT)) {
			/*
		 	 * try to fix up partial writes which are not BLKMULT
			 * in size by forcing the runt record to next archive
			 * volume
		 	 */
			if ((cpos = lseek(arfd, (off_t)0L, SEEK_CUR)) < 0)
				break;
			cpos -= (off_t)res;
			if (ftruncate(arfd, cpos) < 0)
				break;
			res = lstrval = 0;
			break;
		}
		if (res >= 0)
			break;
		/*
		 * if file is out of space, handle it like a return of 0
		 */
		if ((errno == ENOSPC) || (errno == EFBIG) || (errno == EDQUOT))
			res = lstrval = 0;
		break;
	case ISTAPE:
	case ISCHR:
	case ISBLK:
		if (res >= 0)
			break;
		if (errno == EACCES) {
			warn(0, "Write failed, archive is write protected.");
			res = lstrval = 0;
			return(0);
		}
		/*
		 * see if we reached the end of media, if so force a change to
		 * the next volume
		 */
		if ((errno == ENOSPC) || (errno == EIO) || (errno == ENXIO))
			res = lstrval = 0;
		break;
	case ISPIPE:
	default:
		/*
		 * we cannot fix errors to these devices
		 */
		break;
	}

	/*
	 * Better tell the user the bad news...
	 * if this is a block aligned archive format, we may have a bad archive
	 * if the format wants the header to start at a BLKMULT boundry. While
	 * we can deal with the mis-aligned data, it violates spec and other
	 * archive readers will likely fail. if the format is not block
	 * aligned, the user may be lucky (and the archive is ok).
	 */
	if (res >= 0) {
		if (res > 0)
			wr_trail = 1;
		io_ok = 1;
	}

	/*
	 * If we were trying to rewrite the trailer and it didn't work, we
	 * must quit right away.
	 */
	if (!wr_trail && (res <= 0)) {
		warn(1,"Unable to append, trailer re-write failed. Quitting.");
		return(res);
	}
		
	if (res == 0) 
		warn(0, "End of archive volume %d reached", arvol);
	else if (res < 0)
		syswarn(1, errno, "Failed write to archive volume: %d", arvol);
	else if (!frmt->blkalgn || ((res % frmt->blkalgn) == 0))
		warn(0,"WARNING: partial archive write. Archive MAY BE FLAWED");
	else
		warn(1,"WARNING: partial archive write. Archive IS FLAWED");
	return(res);
}

/*
 * ar_rdsync()
 *	Try to move past a bad spot on a flawed archive as needed to continue
 *	I/O. Clears error flags to allow I/O to continue.
 * Return:
 *	0 when ok to try i/o again, -1 otherwise.
 */

#if __STDC__
int
ar_rdsync(void)
#else
int
ar_rdsync()
#endif
{
	long fsbz;
	off_t cpos;
	off_t mpos;
        struct mtop mb;

	/*
	 * Fail resync attempts at user request (done) or this is going to be
	 * an update/append to a existing archive. if last i/o hit media end,
	 * we need to go to the next volume not try a resync
	 */
	if ((done > 0) || (lstrval == 0))
		return(-1);

	if ((act == APPND) || (act == ARCHIVE)) {
		warn(1, "Cannot allow updates to an archive with flaws.");
		return(-1);
	}
	if (io_ok)
		did_io = 1;

	switch(artyp) {
	case ISTAPE:
		/*
		 * if the last i/o was a successful data transfer, we assume
		 * the fault is just a bad record on the tape that we are now
		 * past. If we did not get any data since the last resync try
		 * to move the tape foward one PHYSICAL record past any
		 * damaged tape section. Some tape drives are stubborn and need
		 * to be pushed.
		 */
		if (io_ok) {
			io_ok = 0;
			lstrval = 1;
			break;
		}
		mb.mt_op = MTFSR;
		mb.mt_count = 1;
		if (ioctl(arfd, MTIOCTOP, &mb) < 0)
			break;
		lstrval = 1;
		break;
	case ISREG:
	case ISCHR:
	case ISBLK:
		/*
		 * try to step over the bad part of the device.
		 */
		io_ok = 0;
		if (((fsbz = arsb.st_blksize) <= 0) || (artyp != ISREG))
			fsbz = BLKMULT;
		if ((cpos = lseek(arfd, (off_t)0L, SEEK_CUR)) < 0)
			break;
		mpos = fsbz - (cpos % (off_t)fsbz);
		if (lseek(arfd, mpos, SEEK_CUR) < 0) 
			break;
		lstrval = 1;
		break;
	case ISPIPE:
	default:
		/*
		 * cannot recover on these archive device types
		 */
		io_ok = 0;
		break;
	}
	if (lstrval <= 0) {
		warn(1, "Unable to recover from an archive read failure.");
		return(-1);
	}
	warn(0, "Attempting to recover from an archive read failure.");
	return(0);
}

/*
 * ar_fow()
 *	Move the I/O position within the archive foward the specified number of
 *	bytes as supported by the device. If we cannot move the requested
 *	number of bytes, return the actual number of bytes moved in skipped.
 * Return:
 *	0 if moved the requested distance, -1 on complete failure, 1 on
 *	partial move (the amount moved is in skipped)
 */

#if __STDC__
int
ar_fow(off_t sksz, off_t *skipped)
#else
int
ar_fow(sksz, skipped)
	off_t sksz;
	off_t *skipped;
#endif
{
	off_t cpos;
	off_t mpos;

	*skipped = 0;
	if (sksz <= 0)
		return(0);

	/*
	 * we cannot move foward at EOF or error
	 */
	if (lstrval <= 0)
		return(lstrval);

	/*
	 * Safer to read forward on devices where it is hard to find the end of
	 * the media without reading to it. With tapes we cannot be sure of the
	 * number of physical blocks to skip (we do not know physical block
	 * size at this point), so we must only read foward on tapes!
	 */
	if (artyp != ISREG) 
		return(0);

	/*
	 * figure out where we are in the archive
	 */
	if ((cpos = lseek(arfd, (off_t)0L, SEEK_CUR)) >= 0) {
		/* 
	 	 * we can be asked to move farther than there are bytes in this
		 * volume, if so, just go to file end and let normal buf_fill()