1explain_select(3) Library Functions Manual explain_select(3)
2
6 explain_select - explain select(2) errors
7
9 #include <sys/select.h> #include <libexplain/select.h>
10 const char *explain_select(int nfds, fd_set *readfds, fd_set *writefds,
11 fd_set *exceptfds, struct timeval *timeout);
12 const char *explain_errno_select(int errnum, int nfds, fd_set *readfds,
13 fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);
14 void explain_message_select(char *message, int message_size, int nfds,
15 fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval
16 *timeout);
17 void explain_message_errno_select(char *message, int message_size, int
18 errnum, int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
19 struct timeval *timeout);
20
22 These functions may be used to obtain explanations for errors returned
23 by the select(2) system call.
24 explain_select
26 const char *explain_select(int nfds, fd_set *readfds, fd_set *writefds,
27 fd_set *exceptfds, struct timeval *timeout);
28 The explain_select function is used to obtain an explanation of an
30 error returned by the select(2) system call. The least the message
31 will contain is the value of strerror(errno), but usually it will do
32 much better, and indicate the underlying cause in more detail.
33 The errno global variable will be used to obtain the error value to be
35 decoded.
36 This function is intended to be used in a fashion similar to the fol‐
38 lowing example:
39 if (select(nfds, readfds, writefds, exceptfds, timeout) < 0)
40 {
41 fprintf(stderr, "%s\n", explain_select(nfds,
42 readfds, writefds, exceptfds, timeout));
43 exit(EXIT_FAILURE);
44 }
45 nfds The original nfds, exactly as passed to the select(2) system
47 call.
48 readfds The original readfds, exactly as passed to the select(2) system
50 call.
51 writefds
53 The original writefds, exactly as passed to the select(2) sys‐
54 tem call.
55 exceptfds
57 The original exceptfds, exactly as passed to the select(2) sys‐
58 tem call.
59 timeout The original timeout, exactly as passed to the select(2) system
61 call.
62 Returns:
64 The message explaining the error. This message buffer is
65 shared by all libexplain functions which do not supply a buffer
66 in their argument list. This will be overwritten by the next
67 call to any libexplain function which shares this buffer,
68 including other threads.
69 Note: This function is not thread safe, because it shares a return buf‐
71 fer across all threads, and many other functions in this library.
72 explain_errno_select
74 const char *explain_errno_select(int errnum, int nfds, fd_set *readfds,
75 fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);
76 The explain_errno_select function is used to obtain an explanation of
78 an error returned by the select(2) system call. The least the message
79 will contain is the value of strerror(errnum), but usually it will do
80 much better, and indicate the underlying cause in more detail.
81 This function is intended to be used in a fashion similar to the fol‐
83 lowing example:
84 if (select(nfds, readfds, writefds, exceptfds, timeout) < 0)
85 {
86 int err = errno;
87 fprintf(stderr, "%s\n", explain_errno_select(err,
88 nfds, readfds, writefds, exceptfds, timeout));
89 exit(EXIT_FAILURE);
90 }
91 errnum The error value to be decoded, usually obtained from the errno
93 global variable just before this function is called. This is
94 necessary if you need to call any code between the system call
95 to be explained and this function, because many libc functions
96 will alter the value of errno.
97 nfds The original nfds, exactly as passed to the select(2) system
99 call.
100 readfds The original readfds, exactly as passed to the select(2) system
102 call.
103 writefds
105 The original writefds, exactly as passed to the select(2) sys‐
106 tem call.
107 exceptfds
109 The original exceptfds, exactly as passed to the select(2) sys‐
110 tem call.
111 timeout The original timeout, exactly as passed to the select(2) system
113 call.
114 Returns:
116 The message explaining the error. This message buffer is
117 shared by all libexplain functions which do not supply a buffer
118 in their argument list. This will be overwritten by the next
119 call to any libexplain function which shares this buffer,
120 including other threads.
121 Note: This function is not thread safe, because it shares a return buf‐
123 fer across all threads, and many other functions in this library.
124 explain_message_select
126 void explain_message_select(char *message, int message_size, int nfds,
127 fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval
128 *timeout);
129 The explain_message_select function may be used to obtain an explana‐
131 tion of an error returned by the select(2) system call. The least the
132 message will contain is the value of strerror(errno), but usually it
133 will do much better, and indicate the underlying cause in more detail.
134 The errno global variable will be used to obtain the error value to be
136 decoded.
137 This function is intended to be used in a fashion similar to the fol‐
139 lowing example:
140 if (select(nfds, readfds, writefds, exceptfds, timeout) < 0)
141 {
142 char message[3000];
143 explain_message_select(message, sizeof(message),
144 nfds, readfds, writefds, exceptfds, timeout);
145 fprintf(stderr, "%s\n", message);
146 exit(EXIT_FAILURE);
147 }
148 message The location in which to store the returned message. If a
150 suitable message return buffer is supplied, this function is
151 thread safe.
152 message_size
154 The size in bytes of the location in which to store the
155 returned message.
156 nfds The original nfds, exactly as passed to the select(2) system
158 call.
159 readfds The original readfds, exactly as passed to the select(2) system
161 call.
162 writefds
164 The original writefds, exactly as passed to the select(2) sys‐
165 tem call.
166 exceptfds
168 The original exceptfds, exactly as passed to the select(2) sys‐
169 tem call.
170 timeout The original timeout, exactly as passed to the select(2) system
172 call.
173 explain_message_errno_select
175 void explain_message_errno_select(char *message, int message_size, int
176 errnum, int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
177 struct timeval *timeout);
178 The explain_message_errno_select function may be used to obtain an
180 explanation of an error returned by the select(2) system call. The
181 least the message will contain is the value of strerror(errnum), but
182 usually it will do much better, and indicate the underlying cause in
183 more detail.
184 This function is intended to be used in a fashion similar to the fol‐
186 lowing example:
187 if (select(nfds, readfds, writefds, exceptfds, timeout) < 0)
188 {
189 int err = errno;
190 char message[3000];
191 explain_message_errno_select(message, sizeof(message), err,
192 nfds, readfds, writefds, exceptfds, timeout);
193 fprintf(stderr, "%s\n", message);
194 exit(EXIT_FAILURE);
195 }
196 message The location in which to store the returned message. If a
198 suitable message return buffer is supplied, this function is
199 thread safe.
200 message_size
202 The size in bytes of the location in which to store the
203 returned message.
204 errnum The error value to be decoded, usually obtained from the errno
206 global variable just before this function is called. This is
207 necessary if you need to call any code between the system call
208 to be explained and this function, because many libc functions
209 will alter the value of errno.
210 nfds The original nfds, exactly as passed to the select(2) system
212 call.
213 readfds The original readfds, exactly as passed to the select(2) system
215 call.
216 writefds
218 The original writefds, exactly as passed to the select(2) sys‐
219 tem call.
220 exceptfds
222 The original exceptfds, exactly as passed to the select(2) sys‐
223 tem call.
224 timeout The original timeout, exactly as passed to the select(2) system
226 call.
227
229 select(2)
230 blah blah
231 explain_select_or_die(3)
233 blah blah and report errors
234
236 libexplain version 1.4
237 Copyright (C) 2008 Peter Miller
238 explain_select(3)