2 Unix SMB/Netbios implementation.
4 Samba select/poll implementation
5 Copyright (C) Andrew Tridgell 1992-1998
7 This program is free software; you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation; either version 3 of the License, or
10 (at your option) any later version.
12 This program is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>.
23 /* This is here because it allows us to avoid a nasty race in signal handling.
24 We need to guarantee that when we get a signal we get out of a select immediately
25 but doing that involves a race condition. We can avoid the race by getting the
26 signal handler to write to a pipe that is in the select/poll list
28 This means all Samba signal handlers should call sys_select_signal().
31 static pid_t initialised;
32 static int select_pipe[2];
33 static volatile unsigned pipe_written, pipe_read;
35 /*******************************************************************
36 Call this from all Samba signal handlers if you want to avoid a
37 nasty signal race condition.
38 ********************************************************************/
40 void sys_select_signal(char c)
42 int saved_errno = errno;
44 if (!initialised) return;
46 if (pipe_written > pipe_read+256) return;
48 if (write(select_pipe[1], &c, 1) == 1) pipe_written++;
53 /*******************************************************************
54 Like select() but avoids the signal race using a pipe
55 it also guuarantees that fds on return only ever contains bits set
56 for file descriptors that were readable.
57 ********************************************************************/
59 int sys_select(int maxfd, fd_set *readfds, fd_set *writefds, fd_set *errorfds, struct timeval *tval)
62 fd_set *readfds2, readfds_buf;
64 if (initialised != sys_getpid()) {
65 if (pipe(select_pipe) == -1)
67 DEBUG(0, ("sys_select: pipe failed (%s)\n",
79 * These next two lines seem to fix a bug with the Linux
80 * 2.0.x kernel (and probably other UNIXes as well) where
81 * the one byte read below can block even though the
82 * select returned that there is data in the pipe and
83 * the pipe_written variable was incremented. Thanks to
84 * HP for finding this one. JRA.
87 if(set_blocking(select_pipe[0],0)==-1)
88 smb_panic("select_pipe[0]: O_NONBLOCK failed");
89 if(set_blocking(select_pipe[1],0)==-1)
90 smb_panic("select_pipe[1]: O_NONBLOCK failed");
92 initialised = sys_getpid();
95 maxfd = MAX(select_pipe[0]+1, maxfd);
97 /* If readfds is NULL we need to provide our own set. */
101 readfds2 = &readfds_buf;
104 FD_SET(select_pipe[0], readfds2);
107 ret = select(maxfd,readfds2,writefds,errorfds,tval);
115 } else if (FD_ISSET(select_pipe[0], readfds2)) {
118 if (read(select_pipe[0], &c, 1) == 1) {
120 /* Mark Weaver <mark-clist@npsl.co.uk> pointed out a critical
121 fix to ensure we don't lose signals. We must always
122 return -1 when the select pipe is set, otherwise if another
123 fd is also ready (so ret == 2) then we used to eat the
124 byte in the pipe and lose the signal. JRA.
128 /* JRA - we can use this to debug the signal messaging... */
129 DEBUG(0,("select got %u signal\n", (unsigned int)c));
133 FD_CLR(select_pipe[0], readfds2);
142 /*******************************************************************
143 Similar to sys_select() but catch EINTR and continue.
144 This is what sys_select() used to do in Samba.
145 ********************************************************************/
147 int sys_select_intr(int maxfd, fd_set *readfds, fd_set *writefds, fd_set *errorfds, struct timeval *tval)
150 fd_set *readfds2, readfds_buf, *writefds2, writefds_buf, *errorfds2, errorfds_buf;
151 struct timeval tval2, *ptval, end_time;
153 readfds2 = (readfds ? &readfds_buf : NULL);
154 writefds2 = (writefds ? &writefds_buf : NULL);
155 errorfds2 = (errorfds ? &errorfds_buf : NULL);
157 GetTimeOfDay(&end_time);
158 end_time.tv_sec += tval->tv_sec;
159 end_time.tv_usec += tval->tv_usec;
160 end_time.tv_sec += end_time.tv_usec / 1000000;
161 end_time.tv_usec %= 1000000;
171 readfds_buf = *readfds;
173 writefds_buf = *writefds;
175 errorfds_buf = *errorfds;
176 if (ptval && (errno == EINTR)) {
177 struct timeval now_time;
180 GetTimeOfDay(&now_time);
181 tdif = usec_time_diff(&end_time, &now_time);
183 ret = 0; /* time expired. */
186 ptval->tv_sec = tdif / 1000000;
187 ptval->tv_usec = tdif % 1000000;
190 /* We must use select and not sys_select here. If we use
191 sys_select we'd lose the fact a signal occurred when sys_select
192 read a byte from the pipe. Fix from Mark Weaver
193 <mark-clist@npsl.co.uk>
195 ret = select(maxfd, readfds2, writefds2, errorfds2, ptval);
196 } while (ret == -1 && errno == EINTR);
199 *readfds = readfds_buf;
201 *writefds = writefds_buf;
203 *errorfds = errorfds_buf;