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FreeBSD hs32.drive.ne.jp 9.1-RELEASE FreeBSD 9.1-RELEASE #1: Wed Jan 14 12:18:08 JST 2015 root@hs32.drive.ne.jp:/sys/amd64/compile/hs32 amd64 |
| Current File : //usr/src/sbin/dump/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: release/9.1.0/sbin/dump/tape.c 217769 2011-01-24 06:17:05Z mckusick $";
#endif /* not lint */
#include <sys/param.h>
#include <sys/socket.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 <time.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);
}