2 Unix SMB/CIFS implementation.
3 Samba select/poll implementation
4 Copyright (C) Andrew Tridgell 1992-1998
6 This program is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 2 of the License, or
9 (at your option) any later version.
11 This program is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program; if not, write to the Free Software
18 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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(void)
43 if (!initialised) return;
45 if (pipe_written > pipe_read+256) return;
47 if (write(select_pipe[1], &c, 1) == 1) pipe_written++;
50 /*******************************************************************
51 Like select() but avoids the signal race using a pipe
52 it also guuarantees that fds on return only ever contains bits set
53 for file descriptors that were readable.
54 ********************************************************************/
56 int sys_select(int maxfd, fd_set *readfds, fd_set *writefds, fd_set *errorfds, struct timeval *tval)
59 fd_set *readfds2, readfds_buf;
61 if (initialised != sys_getpid()) {
65 * These next two lines seem to fix a bug with the Linux
66 * 2.0.x kernel (and probably other UNIXes as well) where
67 * the one byte read below can block even though the
68 * select returned that there is data in the pipe and
69 * the pipe_written variable was incremented. Thanks to
70 * HP for finding this one. JRA.
73 if(set_blocking(select_pipe[0],0)==-1)
74 smb_panic("select_pipe[0]: O_NONBLOCK failed.\n");
75 if(set_blocking(select_pipe[1],0)==-1)
76 smb_panic("select_pipe[1]: O_NONBLOCK failed.\n");
78 initialised = sys_getpid();
81 maxfd = MAX(select_pipe[0]+1, maxfd);
83 /* If readfds is NULL we need to provide our own set. */
87 readfds2 = &readfds_buf;
90 FD_SET(select_pipe[0], readfds2);
93 ret = select(maxfd,readfds2,writefds,errorfds,tval);
103 if (FD_ISSET(select_pipe[0], readfds2)) {
104 FD_CLR(select_pipe[0], readfds2);
114 while (pipe_written != pipe_read) {
116 /* Due to the linux kernel bug in 2.0.x, we
117 * always increment here even if the read failed... */
118 read(select_pipe[0], &c, 1);
127 /*******************************************************************
128 Similar to sys_select() but catch EINTR and continue.
129 This is what sys_select() used to do in Samba.
130 ********************************************************************/
132 int sys_select_intr(int maxfd, fd_set *readfds, fd_set *writefds, fd_set *errorfds, struct timeval *tval)
135 fd_set *readfds2, readfds_buf, *writefds2, writefds_buf, *errorfds2, errorfds_buf;
137 readfds2 = (readfds ? &readfds_buf : NULL);
138 writefds2 = (writefds ? &writefds_buf : NULL);
139 errorfds2 = (errorfds ? &errorfds_buf : NULL);
143 readfds_buf = *readfds;
145 writefds_buf = *writefds;
147 errorfds_buf = *errorfds;
148 ret = sys_select(maxfd, readfds2, writefds2, errorfds2, tval);
149 } while (ret == -1 && errno == EINTR);
152 *readfds = readfds_buf;
154 *writefds = writefds_buf;
156 *errorfds = errorfds_buf;