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/*
* wrbufcore.c
*
* Core of algorithm for writing output to devices which don't like
* constant stopping and starting, such as tape drives. This is:
* Copyright (C) 1997-1998,2000-2001 Ian Jackson <ian@chiark.greenend.org.uk>
*
* writebuffer is part of chiark backup, a system for backing up GNU/Linux
* and other UN*X-compatible machines, as used on chiark.greenend.org.uk.
* chiark backup is:
* Copyright (C) 1997-1998,2000-2001 Ian Jackson <ian@chiark.greenend.org.uk>
* Copyright (C) 1999 Peter Maydell <pmaydell@chiark.greenend.org.uk>
*
* This is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 3,
* or (at your option) any later version.
*
* This is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public
* License along with this file; if not, consult the Free Software
* Foundation's website at www.fsf.org, or the GNU Project website at
* www.gnu.org.
*
*/
#include "rwbuffer.h"
static size_t waitfill;
int writing;
void wrbufcore_startup(void) {
waitfill= (buffersize*3)/4;
writing=0;
maxselfd=0;
}
void fdsetset(int fd, fd_set *set) {
FD_SET(fd,set);
if (fd >= maxselfd) maxselfd= fd+1;
}
void wrbufcore_prepselect(int rdfd, int wrfd) {
FD_ZERO(&readfds);
if (rdfd>=0 && !seeneof && used+1<buffersize) fdsetset(rdfd,&readfds);
FD_ZERO(&writefds);
if (writing) fdsetset(wrfd,&writefds);
}
void wrbufcore_afterselect(int rdfd, int wrfd) {
int r;
if (FD_ISSET(wrfd,&writefds) &&
!(rdfd>=0 && FD_ISSET(rdfd,&readfds)) &&
!used) {
wrbuf_report("stopping");
writing= 0;
FD_CLR(wrfd,&writefds);
}
if (rdfd>=0 && FD_ISSET(rdfd,&readfds)) {
r= read(rdfd,rp,min(buffersize-1-used,buf+buffersize-rp));
if (!r) {
seeneof=1; writing=1;
wrbuf_report("seeneof");
} else if (r<0) {
if (!(errno == EAGAIN || errno == EINTR)) { perror("read"); exit(1); }
} else {
used+= r;
rp+= r;
if (rp == buf+buffersize) rp=buf;
}
if (used > waitfill) {
if (!writing) wrbuf_report("starting");
writing=1;
}
}
if (FD_ISSET(wrfd,&writefds) && used) {
r= write(wrfd,wp,min(used,buf+buffersize-wp));
if (r<=0) {
if (!(errno == EAGAIN || errno == EINTR)) { perror("write"); exit(1); }
} else {
used-= r;
wp+= r;
if (wp == buf+buffersize) wp=buf;
}
}
}
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