1/*
2   Unix SMB/Netbios implementation.
3   Version 3.0
4   Samba select/poll implementation
5   Copyright (C) Andrew Tridgell 1992-1998
6
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.
11
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.
16
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.
20*/
21
22#include "includes.h"
23
24/* This is here because it allows us to avoid a nasty race in signal handling.
25   We need to guarantee that when we get a signal we get out of a select immediately
26   but doing that involves a race condition. We can avoid the race by getting the
27   signal handler to write to a pipe that is in the select/poll list
28
29   This means all Samba signal handlers should call sys_select_signal().
30*/
31
32static pid_t initialised;
33static int select_pipe[2];
34static VOLATILE unsigned pipe_written, pipe_read;
35
36/*******************************************************************
37 Call this from all Samba signal handlers if you want to avoid a
38 nasty signal race condition.
39********************************************************************/
40
41void sys_select_signal(void)
42{
43	char c = 1;
44	if (!initialised) return;
45
46	if (pipe_written > pipe_read+256) return;
47
48	if (write(select_pipe[1], &c, 1) == 1) pipe_written++;
49}
50
51/*******************************************************************
52 Like select() but avoids the signal race using a pipe
53 it also guuarantees that fds on return only ever contains bits set
54 for file descriptors that were readable.
55********************************************************************/
56
57int sys_select(int maxfd, fd_set *readfds, fd_set *writefds, fd_set *errorfds, struct timeval *tval)
58{
59	int ret, saved_errno;
60	fd_set *readfds2, readfds_buf;
61
62	if (initialised != sys_getpid()) {
63		pipe(select_pipe);
64
65		/*
66		 * These next two lines seem to fix a bug with the Linux
67		 * 2.0.x kernel (and probably other UNIXes as well) where
68		 * the one byte read below can block even though the
69		 * select returned that there is data in the pipe and
70		 * the pipe_written variable was incremented. Thanks to
71		 * HP for finding this one. JRA.
72		 */
73
74		if(set_blocking(select_pipe[0],0)==-1)
75			smb_panic("select_pipe[0]: O_NONBLOCK failed.\n");
76		if(set_blocking(select_pipe[1],0)==-1)
77			smb_panic("select_pipe[1]: O_NONBLOCK failed.\n");
78
79		initialised = sys_getpid();
80	}
81
82	maxfd = MAX(select_pipe[0]+1, maxfd);
83
84	/* If readfds is NULL we need to provide our own set. */
85	if (readfds) {
86		readfds2 = readfds;
87	} else {
88		readfds2 = &readfds_buf;
89		FD_ZERO(readfds2);
90	}
91	FD_SET(select_pipe[0], readfds2);
92
93	errno = 0;
94	ret = select(maxfd,readfds2,writefds,errorfds,tval);
95
96	if (ret <= 0) {
97		FD_ZERO(readfds2);
98		if (writefds)
99			FD_ZERO(writefds);
100		if (errorfds)
101			FD_ZERO(errorfds);
102	}
103
104	if (FD_ISSET(select_pipe[0], readfds2)) {
105		char c;
106		saved_errno = errno;
107		if (read(select_pipe[0], &c, 1) == 1) {
108			pipe_read++;
109		}
110		errno = saved_errno;
111		FD_CLR(select_pipe[0], readfds2);
112		ret--;
113		if (ret == 0) {
114			ret = -1;
115			errno = EINTR;
116		}
117	}
118
119	return ret;
120}
121
122/*******************************************************************
123 Similar to sys_select() but catch EINTR and continue.
124 This is what sys_select() used to do in Samba.
125********************************************************************/
126
127int sys_select_intr(int maxfd, fd_set *readfds, fd_set *writefds, fd_set *errorfds, struct timeval *tval)
128{
129	int ret;
130	fd_set *readfds2, readfds_buf, *writefds2, writefds_buf, *errorfds2, errorfds_buf;
131	struct timeval tval2, *ptval, end_time;
132
133	readfds2 = (readfds ? &readfds_buf : NULL);
134	writefds2 = (writefds ? &writefds_buf : NULL);
135	errorfds2 = (errorfds ? &errorfds_buf : NULL);
136	if (tval) {
137		GetTimeOfDay(&end_time);
138		end_time.tv_sec += tval->tv_sec;
139		end_time.tv_usec += tval->tv_usec;
140		end_time.tv_sec += end_time.tv_usec / 1000000;
141		end_time.tv_usec %= 1000000;
142		errno = 0;
143		tval2 = *tval;
144		ptval = &tval2;
145	} else {
146		ptval = NULL;
147	}
148
149	do {
150		if (readfds)
151			readfds_buf = *readfds;
152		if (writefds)
153			writefds_buf = *writefds;
154		if (errorfds)
155			errorfds_buf = *errorfds;
156		if (ptval && (errno == EINTR)) {
157			struct timeval now_time;
158			SMB_BIG_INT tdif;
159
160			GetTimeOfDay(&now_time);
161			tdif = usec_time_diff(&end_time, &now_time);
162			if (tdif <= 0) {
163				ret = 0; /* time expired. */
164				break;
165			}
166			ptval->tv_sec = tdif / 1000000;
167			ptval->tv_usec = tdif % 1000000;
168		}
169
170		ret = sys_select(maxfd, readfds2, writefds2, errorfds2, ptval);
171	} while (ret == -1 && errno == EINTR);
172
173	if (readfds)
174		*readfds = readfds_buf;
175	if (writefds)
176		*writefds = writefds_buf;
177	if (errorfds)
178		*errorfds = errorfds_buf;
179
180	return ret;
181}
182