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 2 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, write to the Free Software
19 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
23 #include "system/filesys.h"
25 /* This is here because it allows us to avoid a nasty race in signal handling.
26 We need to guarantee that when we get a signal we get out of a select immediately
27 but doing that involves a race condition. We can avoid the race by getting the
28 signal handler to write to a pipe that is in the select/poll list
30 This means all Samba signal handlers should call sys_select_signal().
33 static pid_t initialised;
34 static int select_pipe[2];
35 static VOLATILE unsigned pipe_written, pipe_read;
37 /*******************************************************************
38 Call this from all Samba signal handlers if you want to avoid a
39 nasty signal race condition.
40 ********************************************************************/
42 void sys_select_signal(void)
45 if (!initialised) return;
47 if (pipe_written > pipe_read+256) return;
49 if (write(select_pipe[1], &c, 1) == 1) pipe_written++;
52 /*******************************************************************
53 Like select() but avoids the signal race using a pipe
54 it also guarantees that fds on return only ever contains bits set
55 for file descriptors that were readable.
56 ********************************************************************/
58 int sys_select(int maxfd, fd_set *readfds, fd_set *writefds, fd_set *errorfds, struct timeval *tval)
61 fd_set *readfds2, readfds_buf;
63 if (initialised != getpid()) {
67 * These next two lines seem to fix a bug with the Linux
68 * 2.0.x kernel (and probably other UNIXes as well) where
69 * the one byte read below can block even though the
70 * select returned that there is data in the pipe and
71 * the pipe_written variable was incremented. Thanks to
72 * HP for finding this one. JRA.
75 if(set_blocking(select_pipe[0],0)==-1)
76 smb_panic("select_pipe[0]: O_NONBLOCK failed.\n");
77 if(set_blocking(select_pipe[1],0)==-1)
78 smb_panic("select_pipe[1]: O_NONBLOCK failed.\n");
80 initialised = getpid();
83 maxfd = MAX(select_pipe[0]+1, maxfd);
85 /* If readfds is NULL we need to provide our own set. */
89 readfds2 = &readfds_buf;
92 FD_SET(select_pipe[0], readfds2);
95 ret = select(maxfd,readfds2,writefds,errorfds,tval);
103 } else if (FD_ISSET(select_pipe[0], readfds2)) {
106 if (read(select_pipe[0], &c, 1) == 1) {
108 /* Mark Weaver <mark-clist@npsl.co.uk> pointed out a critical
109 fix to ensure we don't lose signals. We must always
110 return -1 when the select pipe is set, otherwise if another
111 fd is also ready (so ret == 2) then we used to eat the
112 byte in the pipe and lose the signal. JRA.
117 FD_CLR(select_pipe[0], readfds2);
126 /*******************************************************************
127 Similar to sys_select() but catch EINTR and continue.
128 This is what sys_select() used to do in Samba.
129 ********************************************************************/
131 int sys_select_intr(int maxfd, fd_set *readfds, fd_set *writefds, fd_set *errorfds, struct timeval *tval)
134 fd_set *readfds2, readfds_buf, *writefds2, writefds_buf, *errorfds2, errorfds_buf;
135 struct timeval tval2, *ptval;
137 readfds2 = (readfds ? &readfds_buf : NULL);
138 writefds2 = (writefds ? &writefds_buf : NULL);
139 errorfds2 = (errorfds ? &errorfds_buf : NULL);
140 ptval = (tval ? &tval2 : NULL);
144 readfds_buf = *readfds;
146 writefds_buf = *writefds;
148 errorfds_buf = *errorfds;
152 /* We must use select and not sys_select here. If we use
153 sys_select we'd lose the fact a signal occurred when sys_select
154 read a byte from the pipe. Fix from Mark Weaver
155 <mark-clist@npsl.co.uk>
158 ret = select(maxfd, readfds2, writefds2, errorfds2, ptval);
159 } while (ret == -1 && errno == EINTR);
162 *readfds = readfds_buf;
164 *writefds = writefds_buf;
166 *errorfds = errorfds_buf;