1explain_wait(3) Library Functions Manual explain_wait(3)
2
6 explain_wait - explain wait(2) errors
7
9 #include <libexplain/wait.h>
10 const char *explain_wait(int *status);
11 const char *explain_errno_wait(int errnum, int *status);
12 void explain_message_wait(char *message, int message_size, int *sta‐
13 tus);
14 void explain_message_errno_wait(char *message, int message_size, int
15 errnum, int *status);
16
18 These functions may be used to obtain explanations for errors returned
19 by the wait(2) system call.
20 explain_wait
22 const char *explain_wait(int *status);
23 The explain_wait function is used to obtain an explanation of an error
25 returned by the wait(2) system call. The least the message will con‐
26 tain is the value of strerror(errno), but usually it will do much bet‐
27 ter, and indicate the underlying cause in more detail.
28 The errno global variable will be used to obtain the error value to be
30 decoded.
31 This function is intended to be used in a fashion similar to the fol‐
33 lowing example:
34 if (wait(status) < 0)
35 {
36 fprintf(stderr, "%s\n", explain_wait(status));
37 exit(EXIT_FAILURE);
38 }
39 status The original status, exactly as passed to the wait(2) system
41 call.
42 Returns:
44 The message explaining the error. This message buffer is
45 shared by all libexplain functions which do not supply a buffer
46 in their argument list. This will be overwritten by the next
47 call to any libexplain function which shares this buffer,
48 including other threads.
49 Note: This function is not thread safe, because it shares a return buf‐
51 fer across all threads, and many other functions in this library.
52 explain_errno_wait
54 const char *explain_errno_wait(int errnum, int *status);
55 The explain_errno_wait function is used to obtain an explanation of an
57 error returned by the wait(2) system call. The least the message will
58 contain is the value of strerror(errnum), but usually it will do much
59 better, and indicate the underlying cause in more detail.
60 This function is intended to be used in a fashion similar to the fol‐
62 lowing example:
63 if (wait(status) < 0)
64 {
65 int err = errno;
66 fprintf(stderr, "%s\n", explain_errno_wait(err, status));
67 exit(EXIT_FAILURE);
68 }
69 errnum The error value to be decoded, usually obtained from the errno
71 global variable just before this function is called. This is
72 necessary if you need to call any code between the system call
73 to be explained and this function, because many libc functions
74 will alter the value of errno.
75 status The original status, exactly as passed to the wait(2) system
77 call.
78 Returns:
80 The message explaining the error. This message buffer is
81 shared by all libexplain functions which do not supply a buffer
82 in their argument list. This will be overwritten by the next
83 call to any libexplain function which shares this buffer,
84 including other threads.
85 Note: This function is not thread safe, because it shares a return buf‐
87 fer across all threads, and many other functions in this library.
88 explain_message_wait
90 void explain_message_wait(char *message, int message_size, int *sta‐
91 tus);
92 The explain_message_wait function may be used to obtain an explanation
94 of an error returned by the wait(2) system call. The least the message
95 will contain is the value of strerror(errno), but usually it will do
96 much better, and indicate the underlying cause in more detail.
97 The errno global variable will be used to obtain the error value to be
99 decoded.
100 This function is intended to be used in a fashion similar to the fol‐
102 lowing example:
103 if (wait(status) < 0)
104 {
105 char message[3000];
106 explain_message_wait(message, sizeof(message), status);
107 fprintf(stderr, "%s\n", message);
108 exit(EXIT_FAILURE);
109 }
110 message The location in which to store the returned message. If a
112 suitable message return buffer is supplied, this function is
113 thread safe.
114 message_size
116 The size in bytes of the location in which to store the
117 returned message.
118 status The original status, exactly as passed to the wait(2) system
120 call.
121 explain_message_errno_wait
123 void explain_message_errno_wait(char *message, int message_size, int
124 errnum, int *status);
125 The explain_message_errno_wait function may be used to obtain an expla‐
127 nation of an error returned by the wait(2) system call. The least the
128 message will contain is the value of strerror(errnum), but usually it
129 will do much better, and indicate the underlying cause in more detail.
130 This function is intended to be used in a fashion similar to the fol‐
132 lowing example:
133 if (wait(status) < 0)
134 {
135 int err = errno;
136 char message[3000];
137 explain_message_errno_wait(message, sizeof(message), err, status);
138 fprintf(stderr, "%s\n", message);
139 exit(EXIT_FAILURE);
140 }
141 message The location in which to store the returned message. If a
143 suitable message return buffer is supplied, this function is
144 thread safe.
145 message_size
147 The size in bytes of the location in which to store the
148 returned message.
149 errnum The error value to be decoded, usually obtained from the errno
151 global variable just before this function is called. This is
152 necessary if you need to call any code between the system call
153 to be explained and this function, because many libc functions
154 will alter the value of errno.
155 status The original status, exactly as passed to the wait(2) system
157 call.
158
160 wait(2) wait for process to change state
161 explain_wait_or_die(3)
163 wait for process to change state and report errors
164
166 libexplain version 1.4
167 Copyright (C) 2008 Peter Miller
168 explain_wait(3)