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Unix SMB/Netbios implementation.
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Samba select/poll implementation
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Copyright (C) Andrew Tridgell 1992-1998
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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/* This is here because it allows us to avoid a nasty race in signal handling.
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We need to guarantee that when we get a signal we get out of a select immediately
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but doing that involves a race condition. We can avoid the race by getting the
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signal handler to write to a pipe that is in the select/poll list
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This means all Samba signal handlers should call sys_select_signal().
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static pid_t initialised;
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static int select_pipe[2];
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static volatile unsigned pipe_written, pipe_read;
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/*******************************************************************
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Call this from all Samba signal handlers if you want to avoid a
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nasty signal race condition.
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********************************************************************/
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void sys_select_signal(char c)
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int saved_errno = errno;
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if (!initialised) return;
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if (pipe_written > pipe_read+256) return;
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if (write(select_pipe[1], &c, 1) == 1) pipe_written++;
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/*******************************************************************
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Like select() but avoids the signal race using a pipe
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it also guuarantees that fds on return only ever contains bits set
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for file descriptors that were readable.
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********************************************************************/
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int sys_select(int maxfd, fd_set *readfds, fd_set *writefds, fd_set *errorfds, struct timeval *tval)
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fd_set *readfds2, readfds_buf;
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if (initialised != sys_getpid()) {
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if (pipe(select_pipe) == -1)
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DEBUG(0, ("sys_select: pipe failed (%s)\n",
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* These next two lines seem to fix a bug with the Linux
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* 2.0.x kernel (and probably other UNIXes as well) where
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* the one byte read below can block even though the
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* select returned that there is data in the pipe and
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* the pipe_written variable was incremented. Thanks to
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* HP for finding this one. JRA.
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if(set_blocking(select_pipe[0],0)==-1)
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smb_panic("select_pipe[0]: O_NONBLOCK failed");
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if(set_blocking(select_pipe[1],0)==-1)
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smb_panic("select_pipe[1]: O_NONBLOCK failed");
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initialised = sys_getpid();
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maxfd = MAX(select_pipe[0]+1, maxfd);
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/* If readfds is NULL we need to provide our own set. */
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readfds2 = &readfds_buf;
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FD_SET(select_pipe[0], readfds2);
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ret = select(maxfd,readfds2,writefds,errorfds,tval);
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} else if (FD_ISSET(select_pipe[0], readfds2)) {
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if (read(select_pipe[0], &c, 1) == 1) {
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/* Mark Weaver <mark-clist@npsl.co.uk> pointed out a critical
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fix to ensure we don't lose signals. We must always
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return -1 when the select pipe is set, otherwise if another
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fd is also ready (so ret == 2) then we used to eat the
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byte in the pipe and lose the signal. JRA.
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/* JRA - we can use this to debug the signal messaging... */
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DEBUG(0,("select got %u signal\n", (unsigned int)c));
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FD_CLR(select_pipe[0], readfds2);
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/*******************************************************************
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Similar to sys_select() but catch EINTR and continue.
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This is what sys_select() used to do in Samba.
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********************************************************************/
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int sys_select_intr(int maxfd, fd_set *readfds, fd_set *writefds, fd_set *errorfds, struct timeval *tval)
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fd_set *readfds2, readfds_buf, *writefds2, writefds_buf, *errorfds2, errorfds_buf;
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struct timeval tval2, *ptval, end_time;
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readfds2 = (readfds ? &readfds_buf : NULL);
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writefds2 = (writefds ? &writefds_buf : NULL);
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errorfds2 = (errorfds ? &errorfds_buf : NULL);
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GetTimeOfDay(&end_time);
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end_time.tv_sec += tval->tv_sec;
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end_time.tv_usec += tval->tv_usec;
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end_time.tv_sec += end_time.tv_usec / 1000000;
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end_time.tv_usec %= 1000000;
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readfds_buf = *readfds;
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writefds_buf = *writefds;
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errorfds_buf = *errorfds;
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if (ptval && (errno == EINTR)) {
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struct timeval now_time;
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GetTimeOfDay(&now_time);
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tdif = usec_time_diff(&end_time, &now_time);
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ret = 0; /* time expired. */
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ptval->tv_sec = tdif / 1000000;
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ptval->tv_usec = tdif % 1000000;
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/* We must use select and not sys_select here. If we use
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sys_select we'd lose the fact a signal occurred when sys_select
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read a byte from the pipe. Fix from Mark Weaver
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<mark-clist@npsl.co.uk>
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ret = select(maxfd, readfds2, writefds2, errorfds2, ptval);
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} while (ret == -1 && errno == EINTR);
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*readfds = readfds_buf;
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*writefds = writefds_buf;
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*errorfds = errorfds_buf;