/* Unix SMB/Netbios implementation. Version 3.0 Samba select/poll implementation Copyright (C) Andrew Tridgell 1992-1998 This program 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 of the License, or (at your option) any later version. This program 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 program. If not, see <http://www.gnu.org/licenses/>. */ #include "includes.h" /* This is here because it allows us to avoid a nasty race in signal handling. We need to guarantee that when we get a signal we get out of a select immediately but doing that involves a race condition. We can avoid the race by getting the signal handler to write to a pipe that is in the select/poll list This means all Samba signal handlers should call sys_select_signal(). */ static pid_t initialised; static int select_pipe[2]; static volatile unsigned pipe_written, pipe_read; /******************************************************************* Call this from all Samba signal handlers if you want to avoid a nasty signal race condition. ********************************************************************/ void sys_select_signal(char c) { int saved_errno = errno; if (!initialised) return; if (pipe_written > pipe_read+256) return; if (write(select_pipe[1], &c, 1) == 1) pipe_written++; errno = saved_errno; } /******************************************************************* Like select() but avoids the signal race using a pipe it also guuarantees that fds on return only ever contains bits set for file descriptors that were readable. ********************************************************************/ int sys_select(int maxfd, fd_set *readfds, fd_set *writefds, fd_set *errorfds, struct timeval *tval) { int ret, saved_errno; fd_set *readfds2, readfds_buf; if (initialised != sys_getpid()) { if (pipe(select_pipe) == -1) { DEBUG(0, ("sys_select: pipe failed (%s)\n", strerror(errno))); if (readfds != NULL) FD_ZERO(readfds); if (writefds != NULL) FD_ZERO(writefds); if (errorfds != NULL) FD_ZERO(errorfds); return -1; } /* * These next two lines seem to fix a bug with the Linux * 2.0.x kernel (and probably other UNIXes as well) where * the one byte read below can block even though the * select returned that there is data in the pipe and * the pipe_written variable was incremented. Thanks to * HP for finding this one. JRA. */ if(set_blocking(select_pipe[0],0)==-1) smb_panic("select_pipe[0]: O_NONBLOCK failed"); if(set_blocking(select_pipe[1],0)==-1) smb_panic("select_pipe[1]: O_NONBLOCK failed"); initialised = sys_getpid(); } maxfd = MAX(select_pipe[0]+1, maxfd); /* If readfds is NULL we need to provide our own set. */ if (readfds) { readfds2 = readfds; } else { readfds2 = &readfds_buf; FD_ZERO(readfds2); } FD_SET(select_pipe[0], readfds2); errno = 0; ret = select(maxfd,readfds2,writefds,errorfds,tval); if (ret <= 0) { FD_ZERO(readfds2); if (writefds) FD_ZERO(writefds); if (errorfds) FD_ZERO(errorfds); } else if (FD_ISSET(select_pipe[0], readfds2)) { char c; saved_errno = errno; if (read(select_pipe[0], &c, 1) == 1) { pipe_read++; /* Mark Weaver <mark-clist@npsl.co.uk> pointed out a critical fix to ensure we don't lose signals. We must always return -1 when the select pipe is set, otherwise if another fd is also ready (so ret == 2) then we used to eat the byte in the pipe and lose the signal. JRA. */ ret = -1; #if 0 /* JRA - we can use this to debug the signal messaging... */ DEBUG(0,("select got %u signal\n", (unsigned int)c)); #endif errno = EINTR; } else { FD_CLR(select_pipe[0], readfds2); ret--; errno = saved_errno; } } return ret; } /******************************************************************* Similar to sys_select() but catch EINTR and continue. This is what sys_select() used to do in Samba. ********************************************************************/ int sys_select_intr(int maxfd, fd_set *readfds, fd_set *writefds, fd_set *errorfds, struct timeval *tval) { int ret; fd_set *readfds2, readfds_buf, *writefds2, writefds_buf, *errorfds2, errorfds_buf; struct timeval tval2, *ptval, end_time; readfds2 = (readfds ? &readfds_buf : NULL); writefds2 = (writefds ? &writefds_buf : NULL); errorfds2 = (errorfds ? &errorfds_buf : NULL); if (tval) { GetTimeOfDay(&end_time); end_time.tv_sec += tval->tv_sec; end_time.tv_usec += tval->tv_usec; end_time.tv_sec += end_time.tv_usec / 1000000; end_time.tv_usec %= 1000000; errno = 0; tval2 = *tval; ptval = &tval2; } else { ptval = NULL; } do { if (readfds) readfds_buf = *readfds; if (writefds) writefds_buf = *writefds; if (errorfds) errorfds_buf = *errorfds; if (ptval && (errno == EINTR)) { struct timeval now_time; int64_t tdif; GetTimeOfDay(&now_time); tdif = usec_time_diff(&end_time, &now_time); if (tdif <= 0) { ret = 0; /* time expired. */ break; } ptval->tv_sec = tdif / 1000000; ptval->tv_usec = tdif % 1000000; } /* We must use select and not sys_select here. If we use sys_select we'd lose the fact a signal occurred when sys_select read a byte from the pipe. Fix from Mark Weaver <mark-clist@npsl.co.uk> */ ret = select(maxfd, readfds2, writefds2, errorfds2, ptval); } while (ret == -1 && errno == EINTR); if (readfds) *readfds = readfds_buf; if (writefds) *writefds = writefds_buf; if (errorfds) *errorfds = errorfds_buf; return ret; }