/* $NetBSD: tape.c,v 1.55 2019/03/01 16:42:11 christos Exp $ */ /*- * 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. * 3. 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. */ #include #ifndef lint #if 0 static char sccsid[] = "@(#)tape.c 8.4 (Berkeley) 5/1/95"; #else __RCSID("$NetBSD: tape.c,v 1.55 2019/03/01 16:42:11 christos Exp $"); #endif #endif /* not lint */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include "dump.h" #include "pathnames.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 const char *host; char *nexttape; static ssize_t atomic_read(int, void *, int); static ssize_t atomic_write(int, const void *, int); static void doslave(int, int); static void enslave(void); static void flushtape(void); static void killall(void); static void proceed(int); static void rollforward(void); static void sigpipe(int); static void tperror(int); /* * 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 { 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]; static int64_t tapea_volume; /* value of spcl.c_tapea at volume start */ 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? */ 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 *) xmalloc((unsigned)(reqsiz + writesize + pgoff + TP_BSIZE)); 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(const char *dp, int isspcl) { slp->req[trecno].dblk = (daddr_t)0; slp->req[trecno].count = 1; *(union u_spcl *)(*(nextblock)++) = *(const union u_spcl *)dp; if (isspcl) lastspclrec = iswap64(spcl.c_tapea); trecno++; spcl.c_tapea = iswap64(iswap64(spcl.c_tapea) +1); if (trecno >= ntrec) flushtape(); } void dumpblock(daddr_t blkno, int size) { int avail, tpblks; daddr_t dblkno; dblkno = fsatoda(ufsib, 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 = iswap64(iswap64(spcl.c_tapea) + avail); if (trecno >= ntrec) flushtape(); dblkno += avail << (tp_bshift - dev_bshift); tpblks -= avail; } } int nogripe = 0; static void tperror(int signo __unused) { if (pipeout) { msg("write error on %s\n", tape); quit("Cannot recover"); /* 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); } static void sigpipe(int signo __unused) { quit("Broken pipe"); } /* * do_stats -- * Update xferrate stats */ time_t do_stats(void) { time_t tnow, ttaken; int64_t blocks; (void)time(&tnow); ttaken = tnow - tstart_volume; blocks = iswap64(spcl.c_tapea) - tapea_volume; msg("Volume %d completed at: %s", tapeno, ctime(&tnow)); if (ttaken > 0) { msg("Volume %d took %d:%02d:%02d\n", tapeno, (int) (ttaken / 3600), (int) ((ttaken % 3600) / 60), (int) (ttaken % 60)); msg("Volume %d transfer rate: %d KB/s\n", tapeno, (int) (blocks / ttaken)); xferrate += blocks / ttaken; } return(tnow); } /* * statussig -- * information message upon receipt of SIGINFO * (derived from optr.c::timeest()) */ void statussig(int notused __unused) { time_t tnow, deltat; char msgbuf[128]; int errno_save; if (blockswritten < 500) return; errno_save = errno; (void) time((time_t *) &tnow); if (tnow <= tstart_volume) return; deltat = tstart_writing - tnow + (1.0 * (tnow - tstart_writing)) / blockswritten * tapesize; (void)snprintf(msgbuf, sizeof(msgbuf), "%3.2f%% done at %ld KB/s, finished in %d:%02d\n", (blockswritten * 100.0) / tapesize, (long)((iswap64(spcl.c_tapea) - tapea_volume) / (tnow - tstart_volume)), (int)(deltat / 3600), (int)((deltat % 3600) / 60)); write(STDERR_FILENO, msgbuf, strlen(msgbuf)); errno = errno_save; } 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, slp->req, siz) != siz) quite(errno, "error writing command pipe"); 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, &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, &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 (iswap32(spcl.c_type) != TS_END) { for (i = 0; i < iswap32(spcl.c_count); i++) if (spcl.c_addr[i] != 0) blks++; } slp->count = lastspclrec + blks + 1 - iswap64(spcl.c_tapea); slp->tapea = iswap64(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(int eject) { 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, &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"); } } (void) close(slaves[f].fd); } while (wait(NULL) >= 0) /* wait for any signals from slaves */ /* void */; if (pipeout) return; msg("Closing %s\n", tape); #ifdef RDUMP if (host) { rmtclose(); while (rmtopen(tape, 0, 0) < 0) sleep(10); if (eflag && eject) { msg("Ejecting %s\n", tape); (void) rmtioctl(MTOFFL, 0); } rmtclose(); return; } #endif (void) close(tapefd); while ((f = open(tape, 0)) < 0) sleep (10); if (eflag && eject) { struct mtop offl; msg("Ejecting %s\n", tape); offl.mt_op = MTOFFL; offl.mt_count = 0; (void) ioctl(f, MTIOCTOP, &offl); } (void) close(f); } void close_rewind(void) { int i, f; trewind(1); (void)do_stats(); if (nexttape) return; if (!nogripe) { msg("Change Volumes: Mount volume #%d\n", tapeno+1); broadcast("CHANGE DUMP VOLUMES!\a\a\n"); } if (lflag) { for (i = 0; i < lflag / 10; i++) { /* wait lflag seconds */ if (host) { if (rmtopen(tape, 0, 0) >= 0) { rmtclose(); return; } } else { if ((f = open(tape, 0)) >= 0) { close(f); return; } } sleep (10); } } while (!query("Is the new volume mounted and ready to go?")) if (query("Do you want to abort?")) { dumpabort(0); /*NOTREACHED*/ } } 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 = iswap64(spcl.c_tapea); spcl.c_tapea = iswap64(slp->tapea); startnewtape(0); spcl.c_tapea = iswap64(savedtapea); lastspclrec = savedtapea - 1; } size = (char *)ntb - (char *)q; if (atomic_write(slp->fd, 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, &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"); } } } /* * 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; int waitforpid; char *p; sig_t interrupt_save; interrupt_save = signal(SIGINT, SIG_IGN); parentpid = getpid(); tapea_volume = iswap64(spcl.c_tapea); (void)time(&tstart_volume); restore_check_point: (void)signal(SIGINT, interrupt_save); /* * All signals are inherited... */ 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); signal(SIGINFO, SIG_IGN); /* only want child's stats */ #ifdef TDEBUG msg("Tape: %d; parent process: %d child process %d\n", tapeno+1, parentpid, childpid); #endif /* TDEBUG */ while ((waitforpid = wait(&status)) != childpid) msg("Parent %d waiting for child %d has another child %d return\n", parentpid, childpid, waitforpid); 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 */ signal(SIGINFO, statussig); /* now want child's stats */ #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/rst0,/dev/rst1", * 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); } #ifdef RDUMP while ((tapefd = (host ? rmtopen(tape, 2, 1) : pipeout ? 1 : open(tape, O_WRONLY|O_CREAT, 0666))) < 0) #else while ((tapefd = (pipeout ? 1 : 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 */ asize = 0; blocksthisvol = 0; if (top) newtape++; /* new tape signal */ spcl.c_count = iswap32(slp->count); /* * measure firstrec in TP_BSIZE units since restore doesn't * know the correct ntrec value... */ spcl.c_firstrec = iswap32(slp->firstrec); spcl.c_volume = iswap32(iswap32(spcl.c_volume) + 1); spcl.c_type = iswap32(TS_TAPE); if (!is_ufs2) spcl.c_flags = iswap32(iswap32(spcl.c_flags) | DR_NEWHEADER); writeheader((ino_t)slp->inode); if (!is_ufs2) spcl.c_flags = iswap32(iswap32(spcl.c_flags) & ~ DR_NEWHEADER); msg("Volume %d started at: %s", tapeno, ctime(&tstart_volume)); 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 { #ifdef DUMP_LFS lfs_wrap_go(); #endif killall(); msg("The ENTIRE dump is aborted.\n"); } #ifdef RDUMP rmtclose(); #endif Exit(X_ABORT); } void Exit(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. */ static void proceed(int signo __unused) { 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_LOCAL, SOCK_STREAM, 0, cmd) < 0 || (slaves[i].pid = fork()) < 0) quite(errno, "too many slaves, %d (recompile smaller)", i); 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 */ signal(SIGINFO, SIG_IGN); doslave(cmd[0], i); Exit(X_FINOK); } } for (i = 0; i < SLAVES; i++) (void) atomic_write(slaves[i].fd, &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 __unused) { int nread, nextslave, size, wrote, eot_count, werror; sigset_t nsigset, osigset; wrote = 0; /* * Need our own seek pointer. */ (void) close(diskfd); if ((diskfd = open(disk_dev, O_RDONLY)) < 0) quite(errno, "slave couldn't reopen disk"); /* * Need the pid of the next slave in the loop... */ if ((nread = atomic_read(cmd, &nextslave, sizeof nextslave)) != sizeof nextslave) { quit("master/slave protocol botched - didn't get pid" " of next slave"); } /* * Get list of blocks to dump, read the blocks into tape buffer */ while ((nread = atomic_read(cmd, 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, slp->tblock[trecno], TP_BSIZE) != TP_BSIZE) quit("master/slave protocol botched"); } } sigemptyset(&nsigset); sigaddset(&nsigset, SIGUSR2); sigprocmask(SIG_BLOCK, &nsigset, &osigset); while (!caught) sigsuspend(&osigset); caught = 0; sigprocmask(SIG_SETMASK, &osigset, NULL); /* Try to write the data... */ eot_count = 0; size = 0; werror = 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); werror = errno; #ifdef WRITEDEBUG fprintf(stderr, "slave %d wrote %d werror %d\n", slave_number, wrote, werror); #endif if (wrote < 0) break; if (wrote == 0) eot_count++; size += wrote; } #ifdef WRITEDEBUG if (size != writesize) fprintf(stderr, "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 && werror == ENOSPC) { wrote = 0; eot_count++; } if (eot_count > 0) size = 0; if (wrote < 0) { (void) kill(master, SIGUSR1); sigemptyset(&nsigset); for (;;) sigsuspend(&nsigset); } else { /* * pass size of write back to master * (for EOT handling) */ (void) atomic_write(cmd, &size, sizeof size); } /* * If partial write, don't want next slave to go. * Also jolts him awake. */ (void) kill(nextslave, SIGUSR2); } printcachestats(); if (nread != 0) quite(errno, "error reading command pipe"); } /* * Since a read from a pipe may not return all we asked for, * loop until the count is satisfied (or error). */ static ssize_t atomic_read(int fd, void *buf, int count) { ssize_t got, need = count; while ((got = read(fd, buf, need)) > 0 && (need -= got) > 0) buf = (char *)buf + got; return (got < 0 ? got : count - need); } /* * Since a write may not write all we ask if we get a signal, * loop until the count is satisfied (or error). */ static ssize_t atomic_write(int fd, const void *buf, int count) { ssize_t got, need = count; while ((got = write(fd, buf, need)) > 0 && (need -= got) > 0) buf = (const char *)buf + got; return (got < 0 ? got : count - need); }