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tape.c

/*-
 * Copyright (c) 1980, 1991, 1993
 *    The Regents of the University of California.  All rights reserved.
 *
 * 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.
 * 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
#if 0
static char sccsid[] = "@(#)tape.c  8.4 (Berkeley) 5/1/95";
#endif
static const char rcsid[] =
  "$FreeBSD: src/sbin/dump/tape.c,v 1.27 2005/03/02 02:30:08 iedowse Exp $";
#endif /* not lint */

#include <sys/param.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <sys/wait.h>
#include <sys/stat.h>

#include <ufs/ufs/dinode.h>
#include <ufs/ffs/fs.h>

#include <protocols/dumprestore.h>

#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <setjmp.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "dump.h"

int   writesize;        /* size of malloc()ed buffer for tape */
int64_t     lastspclrec = -1; /* tape block number of last written header */
int   trecno = 0;       /* next record to write in current block */
extern      long blocksperfile;     /* number of blocks per output file */
long  blocksthisvol;          /* number of blocks on current output file */
extern      int ntrec;        /* blocking factor on tape */
extern      int cartridge;
extern      char *host;
char  *nexttape;
FILE  *popenfp = NULL;

static      int atomic(ssize_t (*)(), int, char *, int);
static      void doslave(int, int);
static      void enslave(void);
static      void flushtape(void);
static      void killall(void);
static      void rollforward(void);

/*
 * Concurrent dump mods (Caltech) - disk block reading and tape writing
 * are exported to several slave processes.  While one slave writes the
 * tape, the others read disk blocks; they pass control of the tape in
 * a ring via signals. The parent process traverses the file system and
 * sends writeheader()'s and lists of daddr's to the slaves via pipes.
 * The following structure defines the instruction packets sent to slaves.
 */
struct req {
      ufs2_daddr_t dblk;
      int count;
};
int reqsiz;

#define SLAVES 3        /* 1 slave writing, 1 reading, 1 for slack */
struct slave {
      int64_t tapea;          /* header number at start of this chunk */
      int64_t firstrec; /* record number of this block */
      int count;        /* count to next header (used for TS_TAPE */
                        /* after EOT) */
      int inode;        /* inode that we are currently dealing with */
      int fd;                 /* FD for this slave */
      int pid;          /* PID for this slave */
      int sent;         /* 1 == we've sent this slave requests */
      char (*tblock)[TP_BSIZE]; /* buffer for data blocks */
      struct req *req;  /* buffer for requests */
} slaves[SLAVES+1];
struct slave *slp;

char  (*nextblock)[TP_BSIZE];

int master;       /* pid of master, for sending error signals */
int tenths;       /* length of tape used per block written */
static volatile sig_atomic_t caught; /* have we caught the signal to proceed? */
static volatile sig_atomic_t ready; /* reached the lock point without having */
                  /* received the SIGUSR2 signal from the prev slave? */
static jmp_buf jmpbuf;  /* where to jump to if we are ready when the */
                  /* SIGUSR2 arrives from the previous slave */

int
alloctape(void)
{
      int pgoff = getpagesize() - 1;
      char *buf;
      int i;

      writesize = ntrec * TP_BSIZE;
      reqsiz = (ntrec + 1) * sizeof(struct req);
      /*
       * CDC 92181's and 92185's make 0.8" gaps in 1600-bpi start/stop mode
       * (see DEC TU80 User's Guide).  The shorter gaps of 6250-bpi require
       * repositioning after stopping, i.e, streaming mode, where the gap is
       * variable, 0.30" to 0.45".  The gap is maximal when the tape stops.
       */
      if (blocksperfile == 0 && !unlimited)
            tenths = writesize / density +
                (cartridge ? 16 : density == 625 ? 5 : 8);
      /*
       * Allocate tape buffer contiguous with the array of instruction
       * packets, so flushtape() can write them together with one write().
       * Align tape buffer on page boundary to speed up tape write().
       */
      for (i = 0; i <= SLAVES; i++) {
            buf = (char *)
                malloc((unsigned)(reqsiz + writesize + pgoff + TP_BSIZE));
            if (buf == NULL)
                  return(0);
            slaves[i].tblock = (char (*)[TP_BSIZE])
                (((long)&buf[ntrec + 1] + pgoff) &~ pgoff);
            slaves[i].req = (struct req *)slaves[i].tblock - ntrec - 1;
      }
      slp = &slaves[0];
      slp->count = 1;
      slp->tapea = 0;
      slp->firstrec = 0;
      nextblock = slp->tblock;
      return(1);
}

void
writerec(char *dp, int isspcl)
{

      slp->req[trecno].dblk = (ufs2_daddr_t)0;
      slp->req[trecno].count = 1;
      /* Can't do a structure assignment due to alignment problems */
      bcopy(dp, *(nextblock)++, sizeof (union u_spcl));
      if (isspcl)
            lastspclrec = spcl.c_tapea;
      trecno++;
      spcl.c_tapea++;
      if (trecno >= ntrec)
            flushtape();
}

void
dumpblock(ufs2_daddr_t blkno, int size)
{
      int avail, tpblks;
      ufs2_daddr_t dblkno;

      dblkno = fsbtodb(sblock, blkno);
      tpblks = size >> tp_bshift;
      while ((avail = MIN(tpblks, ntrec - trecno)) > 0) {
            slp->req[trecno].dblk = dblkno;
            slp->req[trecno].count = avail;
            trecno += avail;
            spcl.c_tapea += avail;
            if (trecno >= ntrec)
                  flushtape();
            dblkno += avail << (tp_bshift - dev_bshift);
            tpblks -= avail;
      }
}

int   nogripe = 0;

void
tperror(int signo __unused)
{

      if (pipeout) {
            msg("write error on %s\n", tape);
            quit("Cannot recover\n");
            /* NOTREACHED */
      }
      msg("write error %ld blocks into volume %d\n", blocksthisvol, tapeno);
      broadcast("DUMP WRITE ERROR!\n");
      if (!query("Do you want to restart?"))
            dumpabort(0);
      msg("Closing this volume.  Prepare to restart with new media;\n");
      msg("this dump volume will be rewritten.\n");
      killall();
      nogripe = 1;
      close_rewind();
      Exit(X_REWRITE);
}

void
sigpipe(int signo __unused)
{

      quit("Broken pipe\n");
}

static void
flushtape(void)
{
      int i, blks, got;
      int64_t lastfirstrec;

      int siz = (char *)nextblock - (char *)slp->req;

      slp->req[trecno].count = 0;               /* Sentinel */

      if (atomic(write, slp->fd, (char *)slp->req, siz) != siz)
            quit("error writing command pipe: %s\n", strerror(errno));
      slp->sent = 1; /* we sent a request, read the response later */

      lastfirstrec = slp->firstrec;

      if (++slp >= &slaves[SLAVES])
            slp = &slaves[0];

      /* Read results back from next slave */
      if (slp->sent) {
            if (atomic(read, slp->fd, (char *)&got, sizeof got)
                != sizeof got) {
                  perror("  DUMP: error reading command pipe in master");
                  dumpabort(0);
            }
            slp->sent = 0;

            /* Check for end of tape */
            if (got < writesize) {
                  msg("End of tape detected\n");

                  /*
                   * Drain the results, don't care what the values were.
                   * If we read them here then trewind won't...
                   */
                  for (i = 0; i < SLAVES; i++) {
                        if (slaves[i].sent) {
                              if (atomic(read, slaves[i].fd,
                                  (char *)&got, sizeof got)
                                  != sizeof got) {
                                    perror("  DUMP: error reading command pipe in master");
                                    dumpabort(0);
                              }
                              slaves[i].sent = 0;
                        }
                  }

                  close_rewind();
                  rollforward();
                  return;
            }
      }

      blks = 0;
      if (spcl.c_type != TS_END) {
            for (i = 0; i < spcl.c_count; i++)
                  if (spcl.c_addr[i] != 0)
                        blks++;
      }
      slp->count = lastspclrec + blks + 1 - spcl.c_tapea;
      slp->tapea = spcl.c_tapea;
      slp->firstrec = lastfirstrec + ntrec;
      slp->inode = curino;
      nextblock = slp->tblock;
      trecno = 0;
      asize += tenths;
      blockswritten += ntrec;
      blocksthisvol += ntrec;
      if (!pipeout && !unlimited && (blocksperfile ?
          (blocksthisvol >= blocksperfile) : (asize > tsize))) {
            close_rewind();
            startnewtape(0);
      }
      timeest();
}

void
trewind(void)
{
      struct stat sb;
      int f;
      int got;

      for (f = 0; f < SLAVES; f++) {
            /*
             * Drain the results, but unlike EOT we DO (or should) care
             * what the return values were, since if we detect EOT after
             * we think we've written the last blocks to the tape anyway,
             * we have to replay those blocks with rollforward.
             *
             * fixme: punt for now.
             */
            if (slaves[f].sent) {
                  if (atomic(read, slaves[f].fd, (char *)&got, sizeof got)
                      != sizeof got) {
                        perror("  DUMP: error reading command pipe in master");
                        dumpabort(0);
                  }
                  slaves[f].sent = 0;
                  if (got != writesize) {
                        msg("EOT detected in last 2 tape records!\n");
                        msg("Use a longer tape, decrease the size estimate\n");
                        quit("or use no size estimate at all.\n");
                  }
            }
            (void) close(slaves[f].fd);
      }
      while (wait((int *)NULL) >= 0)      /* wait for any signals from slaves */
            /* void */;

      if (pipeout)
            return;

      msg("Closing %s\n", tape);

      if (popenout) {
            tapefd = -1;
            (void)pclose(popenfp);
            popenfp = NULL;
            return;
      }
#ifdef RDUMP
      if (host) {
            rmtclose();
            while (rmtopen(tape, 0) < 0)
                  sleep(10);
            rmtclose();
            return;
      }
#endif
      if (fstat(tapefd, &sb) == 0 && S_ISFIFO(sb.st_mode)) {
            (void)close(tapefd);
            return;
      }
      (void) close(tapefd);
      while ((f = open(tape, 0)) < 0)
            sleep (10);
      (void) close(f);
}

void
close_rewind()
{
      time_t tstart_changevol, tend_changevol;

      trewind();
      if (nexttape)
            return;
      (void)time((time_t *)&(tstart_changevol));
      if (!nogripe) {
            msg("Change Volumes: Mount volume #%d\n", tapeno+1);
            broadcast("CHANGE DUMP VOLUMES!\a\a\n");
      }
      while (!query("Is the new volume mounted and ready to go?"))
            if (query("Do you want to abort?")) {
                  dumpabort(0);
                  /*NOTREACHED*/
            }
      (void)time((time_t *)&(tend_changevol));
      if ((tstart_changevol != (time_t)-1) && (tend_changevol != (time_t)-1))
            tstart_writing += (tend_changevol - tstart_changevol);
}

void
rollforward(void)
{
      struct req *p, *q, *prev;
      struct slave *tslp;
      int i, size, got;
      int64_t savedtapea;
      union u_spcl *ntb, *otb;
      tslp = &slaves[SLAVES];
      ntb = (union u_spcl *)tslp->tblock[1];

      /*
       * Each of the N slaves should have requests that need to
       * be replayed on the next tape.  Use the extra slave buffers
       * (slaves[SLAVES]) to construct request lists to be sent to
       * each slave in turn.
       */
      for (i = 0; i < SLAVES; i++) {
            q = &tslp->req[1];
            otb = (union u_spcl *)slp->tblock;

            /*
             * For each request in the current slave, copy it to tslp.
             */

            prev = NULL;
            for (p = slp->req; p->count > 0; p += p->count) {
                  *q = *p;
                  if (p->dblk == 0)
                        *ntb++ = *otb++; /* copy the datablock also */
                  prev = q;
                  q += q->count;
            }
            if (prev == NULL)
                  quit("rollforward: protocol botch");
            if (prev->dblk != 0)
                  prev->count -= 1;
            else
                  ntb--;
            q -= 1;
            q->count = 0;
            q = &tslp->req[0];
            if (i == 0) {
                  q->dblk = 0;
                  q->count = 1;
                  trecno = 0;
                  nextblock = tslp->tblock;
                  savedtapea = spcl.c_tapea;
                  spcl.c_tapea = slp->tapea;
                  startnewtape(0);
                  spcl.c_tapea = savedtapea;
                  lastspclrec = savedtapea - 1;
            }
            size = (char *)ntb - (char *)q;
            if (atomic(write, slp->fd, (char *)q, size) != size) {
                  perror("  DUMP: error writing command pipe");
                  dumpabort(0);
            }
            slp->sent = 1;
            if (++slp >= &slaves[SLAVES])
                  slp = &slaves[0];

            q->count = 1;

            if (prev->dblk != 0) {
                  /*
                   * If the last one was a disk block, make the
                   * first of this one be the last bit of that disk
                   * block...
                   */
                  q->dblk = prev->dblk +
                        prev->count * (TP_BSIZE / DEV_BSIZE);
                  ntb = (union u_spcl *)tslp->tblock;
            } else {
                  /*
                   * It wasn't a disk block.  Copy the data to its
                   * new location in the buffer.
                   */
                  q->dblk = 0;
                  *((union u_spcl *)tslp->tblock) = *ntb;
                  ntb = (union u_spcl *)tslp->tblock[1];
            }
      }
      slp->req[0] = *q;
      nextblock = slp->tblock;
      if (q->dblk == 0)
            nextblock++;
      trecno = 1;

      /*
       * Clear the first slaves' response.  One hopes that it
       * worked ok, otherwise the tape is much too short!
       */
      if (slp->sent) {
            if (atomic(read, slp->fd, (char *)&got, sizeof got)
                != sizeof got) {
                  perror("  DUMP: error reading command pipe in master");
                  dumpabort(0);
            }
            slp->sent = 0;

            if (got != writesize) {
                  quit("EOT detected at start of the tape!\n");
            }
      }
}

/*
 * We implement taking and restoring checkpoints on the tape level.
 * When each tape is opened, a new process is created by forking; this
 * saves all of the necessary context in the parent.  The child
 * continues the dump; the parent waits around, saving the context.
 * If the child returns X_REWRITE, then it had problems writing that tape;
 * this causes the parent to fork again, duplicating the context, and
 * everything continues as if nothing had happened.
 */
void
startnewtape(int top)
{
      int   parentpid;
      int   childpid;
      int   status;
      char  *p;
      sig_t interrupt_save;

      interrupt_save = signal(SIGINT, SIG_IGN);
      parentpid = getpid();

restore_check_point:
      (void)signal(SIGINT, interrupt_save);
      /*
       *    All signals are inherited...
       */
      setproctitle(NULL);     /* Restore the proctitle. */
      childpid = fork();
      if (childpid < 0) {
            msg("Context save fork fails in parent %d\n", parentpid);
            Exit(X_ABORT);
      }
      if (childpid != 0) {
            /*
             *    PARENT:
             *    save the context by waiting
             *    until the child doing all of the work returns.
             *    don't catch the interrupt
             */
            signal(SIGINT, SIG_IGN);
#ifdef TDEBUG
            msg("Tape: %d; parent process: %d child process %d\n",
                  tapeno+1, parentpid, childpid);
#endif /* TDEBUG */
            if (waitpid(childpid, &status, 0) == -1)
                  msg("Waiting for child %d: %s\n", childpid,
                      strerror(errno));
            if (status & 0xFF) {
                  msg("Child %d returns LOB status %o\n",
                        childpid, status&0xFF);
            }
            status = (status >> 8) & 0xFF;
#ifdef TDEBUG
            switch(status) {
                  case X_FINOK:
                        msg("Child %d finishes X_FINOK\n", childpid);
                        break;
                  case X_ABORT:
                        msg("Child %d finishes X_ABORT\n", childpid);
                        break;
                  case X_REWRITE:
                        msg("Child %d finishes X_REWRITE\n", childpid);
                        break;
                  default:
                        msg("Child %d finishes unknown %d\n",
                              childpid, status);
                        break;
            }
#endif /* TDEBUG */
            switch(status) {
                  case X_FINOK:
                        Exit(X_FINOK);
                  case X_ABORT:
                        Exit(X_ABORT);
                  case X_REWRITE:
                        goto restore_check_point;
                  default:
                        msg("Bad return code from dump: %d\n", status);
                        Exit(X_ABORT);
            }
            /*NOTREACHED*/
      } else {    /* we are the child; just continue */
#ifdef TDEBUG
            sleep(4);   /* allow time for parent's message to get out */
            msg("Child on Tape %d has parent %d, my pid = %d\n",
                  tapeno+1, parentpid, getpid());
#endif /* TDEBUG */
            /*
             * If we have a name like "/dev/rmt0,/dev/rmt1",
             * use the name before the comma first, and save
             * the remaining names for subsequent volumes.
             */
            tapeno++;               /* current tape sequence */
            if (nexttape || strchr(tape, ',')) {
                  if (nexttape && *nexttape)
                        tape = nexttape;
                  if ((p = strchr(tape, ',')) != NULL) {
                        *p = '\0';
                        nexttape = p + 1;
                  } else
                        nexttape = NULL;
                  msg("Dumping volume %d on %s\n", tapeno, tape);
            }
            if (pipeout) {
                  tapefd = STDOUT_FILENO;
            } else if (popenout) {
                  char volno[sizeof("2147483647")];

                  (void)sprintf(volno, "%d", spcl.c_volume + 1);
                  if (setenv("DUMP_VOLUME", volno, 1) == -1) {
                        msg("Cannot set $DUMP_VOLUME.\n");
                        dumpabort(0);
                  }
                  popenfp = popen(popenout, "w");
                  if (popenfp == NULL) {
                        msg("Cannot open output pipeline \"%s\".\n",
                            popenout);
                        dumpabort(0);
                  }
                  tapefd = fileno(popenfp);
            } else {
#ifdef RDUMP
                  while ((tapefd = (host ? rmtopen(tape, 2) :
                        open(tape, O_WRONLY|O_CREAT, 0666))) < 0)
#else
                  while ((tapefd =
                      open(tape, O_WRONLY|O_CREAT, 0666)) < 0)
#endif
                      {
                        msg("Cannot open output \"%s\".\n", tape);
                        if (!query("Do you want to retry the open?"))
                              dumpabort(0);
                  }
            }

            enslave();  /* Share open tape file descriptor with slaves */
            if (popenout)
                  close(tapefd);    /* Give up our copy of it. */
            signal(SIGINFO, infosch);

            asize = 0;
            blocksthisvol = 0;
            if (top)
                  newtape++;        /* new tape signal */
            spcl.c_count = slp->count;
            /*
             * measure firstrec in TP_BSIZE units since restore doesn't
             * know the correct ntrec value...
             */
            spcl.c_firstrec = slp->firstrec;
            spcl.c_volume++;
            spcl.c_type = TS_TAPE;
            writeheader((ino_t)slp->inode);
            if (tapeno > 1)
                  msg("Volume %d begins with blocks from inode %d\n",
                        tapeno, slp->inode);
      }
}

void
dumpabort(int signo __unused)
{

      if (master != 0 && master != getpid())
            /* Signals master to call dumpabort */
            (void) kill(master, SIGTERM);
      else {
            killall();
            msg("The ENTIRE dump is aborted.\n");
      }
#ifdef RDUMP
      rmtclose();
#endif
      Exit(X_ABORT);
}

void
Exit(status)
      int status;
{

#ifdef TDEBUG
      msg("pid = %d exits with status %d\n", getpid(), status);
#endif /* TDEBUG */
      exit(status);
}

/*
 * proceed - handler for SIGUSR2, used to synchronize IO between the slaves.
 */
void
proceed(int signo __unused)
{

      if (ready)
            longjmp(jmpbuf, 1);
      caught++;
}

void
enslave(void)
{
      int cmd[2];
      int i, j;

      master = getpid();

      signal(SIGTERM, dumpabort);  /* Slave sends SIGTERM on dumpabort() */
      signal(SIGPIPE, sigpipe);
      signal(SIGUSR1, tperror);    /* Slave sends SIGUSR1 on tape errors */
      signal(SIGUSR2, proceed);    /* Slave sends SIGUSR2 to next slave */

      for (i = 0; i < SLAVES; i++) {
            if (i == slp - &slaves[0]) {
                  caught = 1;
            } else {
                  caught = 0;
            }

            if (socketpair(AF_UNIX, SOCK_STREAM, 0, cmd) < 0 ||
                (slaves[i].pid = fork()) < 0)
                  quit("too many slaves, %d (recompile smaller): %s\n",
                      i, strerror(errno));

            slaves[i].fd = cmd[1];
            slaves[i].sent = 0;
            if (slaves[i].pid == 0) {         /* Slave starts up here */
                  for (j = 0; j <= i; j++)
                          (void) close(slaves[j].fd);
                  signal(SIGINT, SIG_IGN);    /* Master handles this */
                  doslave(cmd[0], i);
                  Exit(X_FINOK);
            }
      }

      for (i = 0; i < SLAVES; i++)
            (void) atomic(write, slaves[i].fd,
                        (char *) &slaves[(i + 1) % SLAVES].pid,
                          sizeof slaves[0].pid);

      master = 0;
}

void
killall(void)
{
      int i;

      for (i = 0; i < SLAVES; i++)
            if (slaves[i].pid > 0) {
                  (void) kill(slaves[i].pid, SIGKILL);
                  slaves[i].sent = 0;
            }
}

/*
 * Synchronization - each process has a lockfile, and shares file
 * descriptors to the following process's lockfile.  When our write
 * completes, we release our lock on the following process's lock-
 * file, allowing the following process to lock it and proceed. We
 * get the lock back for the next cycle by swapping descriptors.
 */
static void
doslave(int cmd, int slave_number)
{
      int nread;
      int nextslave, size, wrote, eot_count;

      /*
       * Need our own seek pointer.
       */
      (void) close(diskfd);
      if ((diskfd = open(disk, O_RDONLY)) < 0)
            quit("slave couldn't reopen disk: %s\n", strerror(errno));

      /*
       * Need the pid of the next slave in the loop...
       */
      if ((nread = atomic(read, cmd, (char *)&nextslave, sizeof nextslave))
          != sizeof nextslave) {
            quit("master/slave protocol botched - didn't get pid of next slave.\n");
      }

      /*
       * Get list of blocks to dump, read the blocks into tape buffer
       */
      while ((nread = atomic(read, cmd, (char *)slp->req, reqsiz)) == reqsiz) {
            struct req *p = slp->req;

            for (trecno = 0; trecno < ntrec;
                 trecno += p->count, p += p->count) {
                  if (p->dblk) {
                        bread(p->dblk, slp->tblock[trecno],
                              p->count * TP_BSIZE);
                  } else {
                        if (p->count != 1 || atomic(read, cmd,
                            (char *)slp->tblock[trecno],
                            TP_BSIZE) != TP_BSIZE)
                               quit("master/slave protocol botched.\n");
                  }
            }
            if (setjmp(jmpbuf) == 0) {
                  ready = 1;
                  if (!caught)
                        (void) pause();
            }
            ready = 0;
            caught = 0;

            /* Try to write the data... */
            eot_count = 0;
            size = 0;

            wrote = 0;
            while (eot_count < 10 && size < writesize) {
#ifdef RDUMP
                  if (host)
                        wrote = rmtwrite(slp->tblock[0]+size,
                            writesize-size);
                  else
#endif
                        wrote = write(tapefd, slp->tblock[0]+size,
                            writesize-size);
#ifdef WRITEDEBUG
                  printf("slave %d wrote %d\n", slave_number, wrote);
#endif
                  if (wrote < 0)
                        break;
                  if (wrote == 0)
                        eot_count++;
                  size += wrote;
            }

#ifdef WRITEDEBUG
            if (size != writesize)
             printf("slave %d only wrote %d out of %d bytes and gave up.\n",
                 slave_number, size, writesize);
#endif

            /*
             * Handle ENOSPC as an EOT condition.
             */
            if (wrote < 0 && errno == ENOSPC) {
                  wrote = 0;
                  eot_count++;
            }

            if (eot_count > 0)
                  size = 0;

            if (wrote < 0) {
                  (void) kill(master, SIGUSR1);
                  for (;;)
                        (void) sigpause(0);
            } else {
                  /*
                   * pass size of write back to master
                   * (for EOT handling)
                   */
                  (void) atomic(write, cmd, (char *)&size, sizeof size);
            }

            /*
             * If partial write, don't want next slave to go.
             * Also jolts him awake.
             */
            (void) kill(nextslave, SIGUSR2);
      }
      if (nread != 0)
            quit("error reading command pipe: %s\n", strerror(errno));
}

/*
 * Since a read from a pipe may not return all we asked for,
 * or a write may not write all we ask if we get a signal,
 * loop until the count is satisfied (or error).
 */
static int
atomic(ssize_t (*func)(), int fd, char *buf, int count)
{
      int got, need = count;

      while ((got = (*func)(fd, buf, need)) > 0 && (need -= got) > 0)
            buf += got;
      return (got < 0 ? got : count - need);
}

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