tape.c revision 99530
1/*-
2 * Copyright (c) 1980, 1991, 1993
3 *	The Regents of the University of California.  All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 * 3. All advertising materials mentioning features or use of this software
14 *    must display the following acknowledgement:
15 *	This product includes software developed by the University of
16 *	California, Berkeley and its contributors.
17 * 4. Neither the name of the University nor the names of its contributors
18 *    may be used to endorse or promote products derived from this software
19 *    without specific prior written permission.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 * SUCH DAMAGE.
32 */
33
34#ifndef lint
35#if 0
36static char sccsid[] = "@(#)tape.c	8.4 (Berkeley) 5/1/95";
37#endif
38static const char rcsid[] =
39  "$FreeBSD: head/sbin/dump/tape.c 99530 2002-07-07 12:30:20Z iedowse $";
40#endif /* not lint */
41
42#include <sys/param.h>
43#include <sys/socket.h>
44#include <sys/time.h>
45#include <sys/wait.h>
46#include <sys/stat.h>
47
48#include <ufs/ufs/dinode.h>
49#include <ufs/ffs/fs.h>
50
51#include <protocols/dumprestore.h>
52
53#include <errno.h>
54#include <fcntl.h>
55#include <setjmp.h>
56#include <signal.h>
57#include <stdio.h>
58#include <stdlib.h>
59#include <string.h>
60#include <unistd.h>
61
62#include "dump.h"
63
64int	writesize;		/* size of malloc()ed buffer for tape */
65int64_t	lastspclrec = -1;	/* tape block number of last written header */
66int	trecno = 0;		/* next record to write in current block */
67extern	long blocksperfile;	/* number of blocks per output file */
68long	blocksthisvol;		/* number of blocks on current output file */
69extern	int ntrec;		/* blocking factor on tape */
70extern	int cartridge;
71extern	char *host;
72char	*nexttape;
73
74static	int atomic(ssize_t (*)(), int, char *, int);
75static	void doslave(int, int);
76static	void enslave(void);
77static	void flushtape(void);
78static	void killall(void);
79static	void rollforward(void);
80
81/*
82 * Concurrent dump mods (Caltech) - disk block reading and tape writing
83 * are exported to several slave processes.  While one slave writes the
84 * tape, the others read disk blocks; they pass control of the tape in
85 * a ring via signals. The parent process traverses the filesystem and
86 * sends writeheader()'s and lists of daddr's to the slaves via pipes.
87 * The following structure defines the instruction packets sent to slaves.
88 */
89struct req {
90	ufs2_daddr_t dblk;
91	int count;
92};
93int reqsiz;
94
95#define SLAVES 3		/* 1 slave writing, 1 reading, 1 for slack */
96struct slave {
97	int64_t tapea;		/* header number at start of this chunk */
98	int64_t firstrec;	/* record number of this block */
99	int count;		/* count to next header (used for TS_TAPE */
100				/* after EOT) */
101	int inode;		/* inode that we are currently dealing with */
102	int fd;			/* FD for this slave */
103	int pid;		/* PID for this slave */
104	int sent;		/* 1 == we've sent this slave requests */
105	char (*tblock)[TP_BSIZE]; /* buffer for data blocks */
106	struct req *req;	/* buffer for requests */
107} slaves[SLAVES+1];
108struct slave *slp;
109
110char	(*nextblock)[TP_BSIZE];
111
112int master;		/* pid of master, for sending error signals */
113int tenths;		/* length of tape used per block written */
114static int caught;	/* have we caught the signal to proceed? */
115static int ready;	/* have we reached the lock point without having */
116			/* received the SIGUSR2 signal from the prev slave? */
117static jmp_buf jmpbuf;	/* where to jump to if we are ready when the */
118			/* SIGUSR2 arrives from the previous slave */
119
120int
121alloctape(void)
122{
123	int pgoff = getpagesize() - 1;
124	char *buf;
125	int i;
126
127	writesize = ntrec * TP_BSIZE;
128	reqsiz = (ntrec + 1) * sizeof(struct req);
129	/*
130	 * CDC 92181's and 92185's make 0.8" gaps in 1600-bpi start/stop mode
131	 * (see DEC TU80 User's Guide).  The shorter gaps of 6250-bpi require
132	 * repositioning after stopping, i.e, streaming mode, where the gap is
133	 * variable, 0.30" to 0.45".  The gap is maximal when the tape stops.
134	 */
135	if (blocksperfile == 0 && !unlimited)
136		tenths = writesize / density +
137		    (cartridge ? 16 : density == 625 ? 5 : 8);
138	/*
139	 * Allocate tape buffer contiguous with the array of instruction
140	 * packets, so flushtape() can write them together with one write().
141	 * Align tape buffer on page boundary to speed up tape write().
142	 */
143	for (i = 0; i <= SLAVES; i++) {
144		buf = (char *)
145		    malloc((unsigned)(reqsiz + writesize + pgoff + TP_BSIZE));
146		if (buf == NULL)
147			return(0);
148		slaves[i].tblock = (char (*)[TP_BSIZE])
149		    (((long)&buf[ntrec + 1] + pgoff) &~ pgoff);
150		slaves[i].req = (struct req *)slaves[i].tblock - ntrec - 1;
151	}
152	slp = &slaves[0];
153	slp->count = 1;
154	slp->tapea = 0;
155	slp->firstrec = 0;
156	nextblock = slp->tblock;
157	return(1);
158}
159
160void
161writerec(char *dp, int isspcl)
162{
163
164	slp->req[trecno].dblk = (ufs2_daddr_t)0;
165	slp->req[trecno].count = 1;
166	/* Can't do a structure assignment due to alignment problems */
167	bcopy(dp, *(nextblock)++, sizeof (union u_spcl));
168	if (isspcl)
169		lastspclrec = spcl.c_tapea;
170	trecno++;
171	spcl.c_tapea++;
172	if (trecno >= ntrec)
173		flushtape();
174}
175
176void
177dumpblock(ufs2_daddr_t blkno, int size)
178{
179	int avail, tpblks;
180	ufs2_daddr_t dblkno;
181
182	dblkno = fsbtodb(sblock, blkno);
183	tpblks = size >> tp_bshift;
184	while ((avail = MIN(tpblks, ntrec - trecno)) > 0) {
185		slp->req[trecno].dblk = dblkno;
186		slp->req[trecno].count = avail;
187		trecno += avail;
188		spcl.c_tapea += avail;
189		if (trecno >= ntrec)
190			flushtape();
191		dblkno += avail << (tp_bshift - dev_bshift);
192		tpblks -= avail;
193	}
194}
195
196int	nogripe = 0;
197
198void
199tperror(int signo __unused)
200{
201
202	if (pipeout) {
203		msg("write error on %s\n", tape);
204		quit("Cannot recover\n");
205		/* NOTREACHED */
206	}
207	msg("write error %ld blocks into volume %d\n", blocksthisvol, tapeno);
208	broadcast("DUMP WRITE ERROR!\n");
209	if (!query("Do you want to restart?"))
210		dumpabort(0);
211	msg("Closing this volume.  Prepare to restart with new media;\n");
212	msg("this dump volume will be rewritten.\n");
213	killall();
214	nogripe = 1;
215	close_rewind();
216	Exit(X_REWRITE);
217}
218
219void
220sigpipe(int signo __unused)
221{
222
223	quit("Broken pipe\n");
224}
225
226static void
227flushtape(void)
228{
229	int i, blks, got;
230	int64_t lastfirstrec;
231
232	int siz = (char *)nextblock - (char *)slp->req;
233
234	slp->req[trecno].count = 0;			/* Sentinel */
235
236	if (atomic(write, slp->fd, (char *)slp->req, siz) != siz)
237		quit("error writing command pipe: %s\n", strerror(errno));
238	slp->sent = 1; /* we sent a request, read the response later */
239
240	lastfirstrec = slp->firstrec;
241
242	if (++slp >= &slaves[SLAVES])
243		slp = &slaves[0];
244
245	/* Read results back from next slave */
246	if (slp->sent) {
247		if (atomic(read, slp->fd, (char *)&got, sizeof got)
248		    != sizeof got) {
249			perror("  DUMP: error reading command pipe in master");
250			dumpabort(0);
251		}
252		slp->sent = 0;
253
254		/* Check for end of tape */
255		if (got < writesize) {
256			msg("End of tape detected\n");
257
258			/*
259			 * Drain the results, don't care what the values were.
260			 * If we read them here then trewind won't...
261			 */
262			for (i = 0; i < SLAVES; i++) {
263				if (slaves[i].sent) {
264					if (atomic(read, slaves[i].fd,
265					    (char *)&got, sizeof got)
266					    != sizeof got) {
267						perror("  DUMP: error reading command pipe in master");
268						dumpabort(0);
269					}
270					slaves[i].sent = 0;
271				}
272			}
273
274			close_rewind();
275			rollforward();
276			return;
277		}
278	}
279
280	blks = 0;
281	if (spcl.c_type != TS_END) {
282		for (i = 0; i < spcl.c_count; i++)
283			if (spcl.c_addr[i] != 0)
284				blks++;
285	}
286	slp->count = lastspclrec + blks + 1 - spcl.c_tapea;
287	slp->tapea = spcl.c_tapea;
288	slp->firstrec = lastfirstrec + ntrec;
289	slp->inode = curino;
290	nextblock = slp->tblock;
291	trecno = 0;
292	asize += tenths;
293	blockswritten += ntrec;
294	blocksthisvol += ntrec;
295	if (!pipeout && !unlimited && (blocksperfile ?
296	    (blocksthisvol >= blocksperfile) : (asize > tsize))) {
297		close_rewind();
298		startnewtape(0);
299	}
300	timeest();
301}
302
303void
304trewind(void)
305{
306	struct stat sb;
307	int f;
308	int got;
309
310	for (f = 0; f < SLAVES; f++) {
311		/*
312		 * Drain the results, but unlike EOT we DO (or should) care
313		 * what the return values were, since if we detect EOT after
314		 * we think we've written the last blocks to the tape anyway,
315		 * we have to replay those blocks with rollforward.
316		 *
317		 * fixme: punt for now.
318		 */
319		if (slaves[f].sent) {
320			if (atomic(read, slaves[f].fd, (char *)&got, sizeof got)
321			    != sizeof got) {
322				perror("  DUMP: error reading command pipe in master");
323				dumpabort(0);
324			}
325			slaves[f].sent = 0;
326			if (got != writesize) {
327				msg("EOT detected in last 2 tape records!\n");
328				msg("Use a longer tape, decrease the size estimate\n");
329				quit("or use no size estimate at all.\n");
330			}
331		}
332		(void) close(slaves[f].fd);
333	}
334	while (wait((int *)NULL) >= 0)	/* wait for any signals from slaves */
335		/* void */;
336
337	if (pipeout)
338		return;
339
340	msg("Closing %s\n", tape);
341
342#ifdef RDUMP
343	if (host) {
344		rmtclose();
345		while (rmtopen(tape, 0) < 0)
346			sleep(10);
347		rmtclose();
348		return;
349	}
350#endif
351	if (fstat(tapefd, &sb) == 0 && S_ISFIFO(sb.st_mode)) {
352		(void)close(tapefd);
353		return;
354	}
355	(void) close(tapefd);
356	while ((f = open(tape, 0)) < 0)
357		sleep (10);
358	(void) close(f);
359}
360
361void
362close_rewind()
363{
364	time_t tstart_changevol, tend_changevol;
365
366	trewind();
367	if (nexttape)
368		return;
369	(void)time((time_t *)&(tstart_changevol));
370	if (!nogripe) {
371		msg("Change Volumes: Mount volume #%d\n", tapeno+1);
372		broadcast("CHANGE DUMP VOLUMES!\a\a\n");
373	}
374	while (!query("Is the new volume mounted and ready to go?"))
375		if (query("Do you want to abort?")) {
376			dumpabort(0);
377			/*NOTREACHED*/
378		}
379	(void)time((time_t *)&(tend_changevol));
380	if ((tstart_changevol != (time_t)-1) && (tend_changevol != (time_t)-1))
381		tstart_writing += (tend_changevol - tstart_changevol);
382}
383
384void
385rollforward(void)
386{
387	struct req *p, *q, *prev;
388	struct slave *tslp;
389	int i, size, got;
390	int64_t savedtapea;
391	union u_spcl *ntb, *otb;
392	tslp = &slaves[SLAVES];
393	ntb = (union u_spcl *)tslp->tblock[1];
394
395	/*
396	 * Each of the N slaves should have requests that need to
397	 * be replayed on the next tape.  Use the extra slave buffers
398	 * (slaves[SLAVES]) to construct request lists to be sent to
399	 * each slave in turn.
400	 */
401	for (i = 0; i < SLAVES; i++) {
402		q = &tslp->req[1];
403		otb = (union u_spcl *)slp->tblock;
404
405		/*
406		 * For each request in the current slave, copy it to tslp.
407		 */
408
409		prev = NULL;
410		for (p = slp->req; p->count > 0; p += p->count) {
411			*q = *p;
412			if (p->dblk == 0)
413				*ntb++ = *otb++; /* copy the datablock also */
414			prev = q;
415			q += q->count;
416		}
417		if (prev == NULL)
418			quit("rollforward: protocol botch");
419		if (prev->dblk != 0)
420			prev->count -= 1;
421		else
422			ntb--;
423		q -= 1;
424		q->count = 0;
425		q = &tslp->req[0];
426		if (i == 0) {
427			q->dblk = 0;
428			q->count = 1;
429			trecno = 0;
430			nextblock = tslp->tblock;
431			savedtapea = spcl.c_tapea;
432			spcl.c_tapea = slp->tapea;
433			startnewtape(0);
434			spcl.c_tapea = savedtapea;
435			lastspclrec = savedtapea - 1;
436		}
437		size = (char *)ntb - (char *)q;
438		if (atomic(write, slp->fd, (char *)q, size) != size) {
439			perror("  DUMP: error writing command pipe");
440			dumpabort(0);
441		}
442		slp->sent = 1;
443		if (++slp >= &slaves[SLAVES])
444			slp = &slaves[0];
445
446		q->count = 1;
447
448		if (prev->dblk != 0) {
449			/*
450			 * If the last one was a disk block, make the
451			 * first of this one be the last bit of that disk
452			 * block...
453			 */
454			q->dblk = prev->dblk +
455				prev->count * (TP_BSIZE / DEV_BSIZE);
456			ntb = (union u_spcl *)tslp->tblock;
457		} else {
458			/*
459			 * It wasn't a disk block.  Copy the data to its
460			 * new location in the buffer.
461			 */
462			q->dblk = 0;
463			*((union u_spcl *)tslp->tblock) = *ntb;
464			ntb = (union u_spcl *)tslp->tblock[1];
465		}
466	}
467	slp->req[0] = *q;
468	nextblock = slp->tblock;
469	if (q->dblk == 0)
470		nextblock++;
471	trecno = 1;
472
473	/*
474	 * Clear the first slaves' response.  One hopes that it
475	 * worked ok, otherwise the tape is much too short!
476	 */
477	if (slp->sent) {
478		if (atomic(read, slp->fd, (char *)&got, sizeof got)
479		    != sizeof got) {
480			perror("  DUMP: error reading command pipe in master");
481			dumpabort(0);
482		}
483		slp->sent = 0;
484
485		if (got != writesize) {
486			quit("EOT detected at start of the tape!\n");
487		}
488	}
489}
490
491/*
492 * We implement taking and restoring checkpoints on the tape level.
493 * When each tape is opened, a new process is created by forking; this
494 * saves all of the necessary context in the parent.  The child
495 * continues the dump; the parent waits around, saving the context.
496 * If the child returns X_REWRITE, then it had problems writing that tape;
497 * this causes the parent to fork again, duplicating the context, and
498 * everything continues as if nothing had happened.
499 */
500void
501startnewtape(int top)
502{
503	int	parentpid;
504	int	childpid;
505	int	status;
506	int	waitpid;
507	char	*p;
508	sig_t	interrupt_save;
509
510	interrupt_save = signal(SIGINT, SIG_IGN);
511	parentpid = getpid();
512
513restore_check_point:
514	(void)signal(SIGINT, interrupt_save);
515	/*
516	 *	All signals are inherited...
517	 */
518	setproctitle(NULL);	/* Restore the proctitle. */
519	childpid = fork();
520	if (childpid < 0) {
521		msg("Context save fork fails in parent %d\n", parentpid);
522		Exit(X_ABORT);
523	}
524	if (childpid != 0) {
525		/*
526		 *	PARENT:
527		 *	save the context by waiting
528		 *	until the child doing all of the work returns.
529		 *	don't catch the interrupt
530		 */
531		signal(SIGINT, SIG_IGN);
532#ifdef TDEBUG
533		msg("Tape: %d; parent process: %d child process %d\n",
534			tapeno+1, parentpid, childpid);
535#endif /* TDEBUG */
536		while ((waitpid = wait(&status)) != childpid)
537			msg("Parent %d waiting for child %d has another child %d return\n",
538				parentpid, childpid, waitpid);
539		if (status & 0xFF) {
540			msg("Child %d returns LOB status %o\n",
541				childpid, status&0xFF);
542		}
543		status = (status >> 8) & 0xFF;
544#ifdef TDEBUG
545		switch(status) {
546			case X_FINOK:
547				msg("Child %d finishes X_FINOK\n", childpid);
548				break;
549			case X_ABORT:
550				msg("Child %d finishes X_ABORT\n", childpid);
551				break;
552			case X_REWRITE:
553				msg("Child %d finishes X_REWRITE\n", childpid);
554				break;
555			default:
556				msg("Child %d finishes unknown %d\n",
557					childpid, status);
558				break;
559		}
560#endif /* TDEBUG */
561		switch(status) {
562			case X_FINOK:
563				Exit(X_FINOK);
564			case X_ABORT:
565				Exit(X_ABORT);
566			case X_REWRITE:
567				goto restore_check_point;
568			default:
569				msg("Bad return code from dump: %d\n", status);
570				Exit(X_ABORT);
571		}
572		/*NOTREACHED*/
573	} else {	/* we are the child; just continue */
574#ifdef TDEBUG
575		sleep(4);	/* allow time for parent's message to get out */
576		msg("Child on Tape %d has parent %d, my pid = %d\n",
577			tapeno+1, parentpid, getpid());
578#endif /* TDEBUG */
579		/*
580		 * If we have a name like "/dev/rmt0,/dev/rmt1",
581		 * use the name before the comma first, and save
582		 * the remaining names for subsequent volumes.
583		 */
584		tapeno++;               /* current tape sequence */
585		if (nexttape || strchr(tape, ',')) {
586			if (nexttape && *nexttape)
587				tape = nexttape;
588			if ((p = strchr(tape, ',')) != NULL) {
589				*p = '\0';
590				nexttape = p + 1;
591			} else
592				nexttape = NULL;
593			msg("Dumping volume %d on %s\n", tapeno, tape);
594		}
595#ifdef RDUMP
596		while ((tapefd = (host ? rmtopen(tape, 2) :
597			pipeout ? 1 : open(tape, O_WRONLY|O_CREAT, 0666))) < 0)
598#else
599		while ((tapefd = (pipeout ? 1 :
600				  open(tape, O_WRONLY|O_CREAT, 0666))) < 0)
601#endif
602		    {
603			msg("Cannot open output \"%s\".\n", tape);
604			if (!query("Do you want to retry the open?"))
605				dumpabort(0);
606		}
607
608		enslave();  /* Share open tape file descriptor with slaves */
609		signal(SIGINFO, infosch);
610
611		asize = 0;
612		blocksthisvol = 0;
613		if (top)
614			newtape++;		/* new tape signal */
615		spcl.c_count = slp->count;
616		/*
617		 * measure firstrec in TP_BSIZE units since restore doesn't
618		 * know the correct ntrec value...
619		 */
620		spcl.c_firstrec = slp->firstrec;
621		spcl.c_volume++;
622		spcl.c_type = TS_TAPE;
623		writeheader((ino_t)slp->inode);
624		if (tapeno > 1)
625			msg("Volume %d begins with blocks from inode %d\n",
626				tapeno, slp->inode);
627	}
628}
629
630void
631dumpabort(int signo __unused)
632{
633
634	if (master != 0 && master != getpid())
635		/* Signals master to call dumpabort */
636		(void) kill(master, SIGTERM);
637	else {
638		killall();
639		msg("The ENTIRE dump is aborted.\n");
640	}
641#ifdef RDUMP
642	rmtclose();
643#endif
644	Exit(X_ABORT);
645}
646
647void
648Exit(status)
649	int status;
650{
651
652#ifdef TDEBUG
653	msg("pid = %d exits with status %d\n", getpid(), status);
654#endif /* TDEBUG */
655	exit(status);
656}
657
658/*
659 * proceed - handler for SIGUSR2, used to synchronize IO between the slaves.
660 */
661void
662proceed(int signo __unused)
663{
664
665	if (ready)
666		longjmp(jmpbuf, 1);
667	caught++;
668}
669
670void
671enslave(void)
672{
673	int cmd[2];
674	int i, j;
675
676	master = getpid();
677
678	signal(SIGTERM, dumpabort);  /* Slave sends SIGTERM on dumpabort() */
679	signal(SIGPIPE, sigpipe);
680	signal(SIGUSR1, tperror);    /* Slave sends SIGUSR1 on tape errors */
681	signal(SIGUSR2, proceed);    /* Slave sends SIGUSR2 to next slave */
682
683	for (i = 0; i < SLAVES; i++) {
684		if (i == slp - &slaves[0]) {
685			caught = 1;
686		} else {
687			caught = 0;
688		}
689
690		if (socketpair(AF_UNIX, SOCK_STREAM, 0, cmd) < 0 ||
691		    (slaves[i].pid = fork()) < 0)
692			quit("too many slaves, %d (recompile smaller): %s\n",
693			    i, strerror(errno));
694
695		slaves[i].fd = cmd[1];
696		slaves[i].sent = 0;
697		if (slaves[i].pid == 0) { 	    /* Slave starts up here */
698			for (j = 0; j <= i; j++)
699			        (void) close(slaves[j].fd);
700			signal(SIGINT, SIG_IGN);    /* Master handles this */
701			doslave(cmd[0], i);
702			Exit(X_FINOK);
703		}
704	}
705
706	for (i = 0; i < SLAVES; i++)
707		(void) atomic(write, slaves[i].fd,
708			      (char *) &slaves[(i + 1) % SLAVES].pid,
709		              sizeof slaves[0].pid);
710
711	master = 0;
712}
713
714void
715killall(void)
716{
717	int i;
718
719	for (i = 0; i < SLAVES; i++)
720		if (slaves[i].pid > 0) {
721			(void) kill(slaves[i].pid, SIGKILL);
722			slaves[i].sent = 0;
723		}
724}
725
726/*
727 * Synchronization - each process has a lockfile, and shares file
728 * descriptors to the following process's lockfile.  When our write
729 * completes, we release our lock on the following process's lock-
730 * file, allowing the following process to lock it and proceed. We
731 * get the lock back for the next cycle by swapping descriptors.
732 */
733static void
734doslave(int cmd, int slave_number)
735{
736	int nread;
737	int nextslave, size, wrote, eot_count;
738
739	/*
740	 * Need our own seek pointer.
741	 */
742	(void) close(diskfd);
743	if ((diskfd = open(disk, O_RDONLY)) < 0)
744		quit("slave couldn't reopen disk: %s\n", strerror(errno));
745
746	/*
747	 * Need the pid of the next slave in the loop...
748	 */
749	if ((nread = atomic(read, cmd, (char *)&nextslave, sizeof nextslave))
750	    != sizeof nextslave) {
751		quit("master/slave protocol botched - didn't get pid of next slave.\n");
752	}
753
754	/*
755	 * Get list of blocks to dump, read the blocks into tape buffer
756	 */
757	while ((nread = atomic(read, cmd, (char *)slp->req, reqsiz)) == reqsiz) {
758		struct req *p = slp->req;
759
760		for (trecno = 0; trecno < ntrec;
761		     trecno += p->count, p += p->count) {
762			if (p->dblk) {
763				bread(p->dblk, slp->tblock[trecno],
764					p->count * TP_BSIZE);
765			} else {
766				if (p->count != 1 || atomic(read, cmd,
767				    (char *)slp->tblock[trecno],
768				    TP_BSIZE) != TP_BSIZE)
769				       quit("master/slave protocol botched.\n");
770			}
771		}
772		if (setjmp(jmpbuf) == 0) {
773			ready = 1;
774			if (!caught)
775				(void) pause();
776		}
777		ready = 0;
778		caught = 0;
779
780		/* Try to write the data... */
781		eot_count = 0;
782		size = 0;
783
784		while (eot_count < 10 && size < writesize) {
785#ifdef RDUMP
786			if (host)
787				wrote = rmtwrite(slp->tblock[0]+size,
788				    writesize-size);
789			else
790#endif
791				wrote = write(tapefd, slp->tblock[0]+size,
792				    writesize-size);
793#ifdef WRITEDEBUG
794			printf("slave %d wrote %d\n", slave_number, wrote);
795#endif
796			if (wrote < 0)
797				break;
798			if (wrote == 0)
799				eot_count++;
800			size += wrote;
801		}
802
803#ifdef WRITEDEBUG
804		if (size != writesize)
805		 printf("slave %d only wrote %d out of %d bytes and gave up.\n",
806		     slave_number, size, writesize);
807#endif
808
809		/*
810		 * Handle ENOSPC as an EOT condition.
811		 */
812		if (wrote < 0 && errno == ENOSPC) {
813			wrote = 0;
814			eot_count++;
815		}
816
817		if (eot_count > 0)
818			size = 0;
819
820		if (wrote < 0) {
821			(void) kill(master, SIGUSR1);
822			for (;;)
823				(void) sigpause(0);
824		} else {
825			/*
826			 * pass size of write back to master
827			 * (for EOT handling)
828			 */
829			(void) atomic(write, cmd, (char *)&size, sizeof size);
830		}
831
832		/*
833		 * If partial write, don't want next slave to go.
834		 * Also jolts him awake.
835		 */
836		(void) kill(nextslave, SIGUSR2);
837	}
838	if (nread != 0)
839		quit("error reading command pipe: %s\n", strerror(errno));
840}
841
842/*
843 * Since a read from a pipe may not return all we asked for,
844 * or a write may not write all we ask if we get a signal,
845 * loop until the count is satisfied (or error).
846 */
847static int
848atomic(ssize_t (*func)(), int fd, char *buf, int count)
849{
850	int got, need = count;
851
852	while ((got = (*func)(fd, buf, need)) > 0 && (need -= got) > 0)
853		buf += got;
854	return (got < 0 ? got : count - need);
855}
856