xserver_poll.c revision 1b5d61b8 
1/*---------------------------------------------------------------------------*\
2  $Id: xserver_poll.c,v 1.1.1.1 2018/12/31 09:36:12 mrg Exp $
3
4  NAME
5
6	poll - select(2)-based poll() emulation function for BSD systems.
7
8  SYNOPSIS
9	#include "poll.h"
10
11	struct pollfd
12	{
13	    int     fd;
14	    short   events;
15	    short   revents;
16	}
17
18	int poll (struct pollfd *pArray, unsigned long n_fds, int timeout)
19
20  DESCRIPTION
21
22	This file, and the accompanying "poll.h", implement the System V
23	poll(2) system call for BSD systems (which typically do not provide
24	poll()).  Poll() provides a method for multiplexing input and output
25	on multiple open file descriptors; in traditional BSD systems, that
26	capability is provided by select().  While the semantics of select()
27	differ from those of poll(), poll() can be readily emulated in terms
28	of select() -- which is how this function is implemented.
29
30  REFERENCES
31	Stevens, W. Richard. Unix Network Programming.  Prentice-Hall, 1990.
32
33  NOTES
34	1. This software requires an ANSI C compiler.
35
36  LICENSE
37
38  This software is released under the following BSD license, adapted from
39  http://opensource.org/licenses/bsd-license.php
40
41  Copyright (c) 1995-2011, Brian M. Clapper
42  All rights reserved.
43
44  Redistribution and use in source and binary forms, with or without
45  modification, are permitted provided that the following conditions are met:
46
47  * Redistributions of source code must retain the above copyright notice,
48    this list of conditions and the following disclaimer.
49
50  * Redistributions in binary form must reproduce the above copyright
51    notice, this list of conditions and the following disclaimer in the
52    documentation and/or other materials provided with the distribution.
53
54  * Neither the name of the clapper.org nor the names of its contributors
55    may be used to endorse or promote products derived from this software
56    without specific prior written permission.
57
58  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
59  IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
60  THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
61  PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
62  CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
63  EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
64  PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
65  PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
66  LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
67  NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
68  SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
69\*---------------------------------------------------------------------------*/
70
71
72/*---------------------------------------------------------------------------*\
73				 Includes
74\*---------------------------------------------------------------------------*/
75
76#ifdef HAVE_DIX_CONFIG_H
77#include <dix-config.h>
78#endif
79
80#include <unistd.h>			     /* standard Unix definitions */
81#include <sys/types.h>                       /* system types */
82#include <sys/time.h>                        /* time definitions */
83#include <assert.h>                          /* assertion macros */
84#include <string.h>                          /* string functions */
85#include "xserver_poll.h"
86
87/*---------------------------------------------------------------------------*\
88				  Macros
89\*---------------------------------------------------------------------------*/
90
91#ifndef MAX
92#define MAX(a,b)	((a) > (b) ? (a) : (b))
93#endif
94
95/*---------------------------------------------------------------------------*\
96			     Private Functions
97\*---------------------------------------------------------------------------*/
98
99static int map_poll_spec
100			(struct pollfd *pArray,
101                         nfds_t         n_fds,
102			  fd_set        *pReadSet,
103			  fd_set        *pWriteSet,
104			  fd_set        *pExceptSet)
105{
106    register nfds_t  i;                      /* loop control */
107    register struct  pollfd *pCur;           /* current array element */
108    register int     max_fd = -1;            /* return value */
109
110    /*
111       Map the poll() structures into the file descriptor sets required
112       by select().
113    */
114    for (i = 0, pCur = pArray; i < n_fds; i++, pCur++)
115    {
116        /* Skip any bad FDs in the array. */
117
118        if (pCur->fd < 0)
119            continue;
120
121	if (pCur->events & POLLIN)
122	{
123	    /* "Input Ready" notification desired. */
124	    FD_SET (pCur->fd, pReadSet);
125	}
126
127	if (pCur->events & POLLOUT)
128	{
129	    /* "Output Possible" notification desired. */
130	    FD_SET (pCur->fd, pWriteSet);
131	}
132
133	if (pCur->events & POLLPRI)
134	{
135	    /*
136	       "Exception Occurred" notification desired.  (Exceptions
137	       include out of band data.
138	    */
139	    FD_SET (pCur->fd, pExceptSet);
140	}
141
142	max_fd = MAX (max_fd, pCur->fd);
143    }
144
145    return max_fd;
146}
147
148static struct timeval *map_timeout
149			(int poll_timeout, struct timeval *pSelTimeout)
150{
151    struct timeval *pResult;
152
153    /*
154       Map the poll() timeout value into a select() timeout.  The possible
155       values of the poll() timeout value, and their meanings, are:
156
157       VALUE	MEANING
158
159       -1	wait indefinitely (until signal occurs)
160        0	return immediately, don't block
161       >0	wait specified number of milliseconds
162
163       select() uses a "struct timeval", which specifies the timeout in
164       seconds and microseconds, so the milliseconds value has to be mapped
165       accordingly.
166    */
167
168    assert (pSelTimeout != (struct timeval *) NULL);
169
170    switch (poll_timeout)
171    {
172	case -1:
173	    /*
174	       A NULL timeout structure tells select() to wait indefinitely.
175	    */
176	    pResult = (struct timeval *) NULL;
177	    break;
178
179	case 0:
180	    /*
181	       "Return immediately" (test) is specified by all zeros in
182	       a timeval structure.
183	    */
184	    pSelTimeout->tv_sec  = 0;
185	    pSelTimeout->tv_usec = 0;
186	    pResult = pSelTimeout;
187	    break;
188
189	default:
190	    /* Wait the specified number of milliseconds. */
191	    pSelTimeout->tv_sec  = poll_timeout / 1000; /* get seconds */
192	    poll_timeout        %= 1000;                /* remove seconds */
193	    pSelTimeout->tv_usec = poll_timeout * 1000; /* get microseconds */
194	    pResult = pSelTimeout;
195	    break;
196    }
197
198
199    return pResult;
200}
201
202static void map_select_results
203			 (struct pollfd *pArray,
204			  unsigned long  n_fds,
205			  fd_set        *pReadSet,
206			  fd_set        *pWriteSet,
207			  fd_set        *pExceptSet)
208{
209    register unsigned long  i;                   /* loop control */
210    register struct	    pollfd *pCur;        /* current array element */
211
212    for (i = 0, pCur = pArray; i < n_fds; i++, pCur++)
213    {
214        /* Skip any bad FDs in the array. */
215
216        if (pCur->fd < 0)
217            continue;
218
219	/* Exception events take priority over input events. */
220
221	pCur->revents = 0;
222	if (FD_ISSET (pCur->fd, pExceptSet))
223	    pCur->revents |= POLLPRI;
224
225	else if (FD_ISSET (pCur->fd, pReadSet))
226	    pCur->revents |= POLLIN;
227
228	if (FD_ISSET (pCur->fd, pWriteSet))
229	    pCur->revents |= POLLOUT;
230    }
231
232    return;
233}
234
235/*---------------------------------------------------------------------------*\
236			     Public Functions
237\*---------------------------------------------------------------------------*/
238
239int xserver_poll
240	(struct pollfd *pArray, unsigned long n_fds, int timeout)
241{
242    fd_set  read_descs;                          /* input file descs */
243    fd_set  write_descs;                         /* output file descs */
244    fd_set  except_descs;                        /* exception descs */
245    struct  timeval stime;                       /* select() timeout value */
246    int	    ready_descriptors;                   /* function result */
247    int	    max_fd;                              /* maximum fd value */
248    struct  timeval *pTimeout;                   /* actually passed */
249
250    FD_ZERO (&read_descs);
251    FD_ZERO (&write_descs);
252    FD_ZERO (&except_descs);
253
254    assert (pArray != (struct pollfd *) NULL);
255
256    /* Map the poll() file descriptor list in the select() data structures. */
257
258    max_fd = map_poll_spec (pArray, n_fds,
259			    &read_descs, &write_descs, &except_descs);
260
261    /* Map the poll() timeout value in the select() timeout structure. */
262
263    pTimeout = map_timeout (timeout, &stime);
264
265    /* Make the select() call. */
266
267    ready_descriptors = select (max_fd + 1, &read_descs, &write_descs,
268				&except_descs, pTimeout);
269
270    if (ready_descriptors >= 0)
271    {
272	map_select_results (pArray, n_fds,
273			    &read_descs, &write_descs, &except_descs);
274    }
275
276    return ready_descriptors;
277}
278