1explain_pread(3) Library Functions Manual explain_pread(3)
2
6 explain_pread - explain pread(2) errors
7
9 #include <libexplain/pread.h>
10 const char *explain_pread(int fildes, void *data, size_t data_size,
11 off_t offset);
12 const char *explain_errno_pread(int errnum, int fildes, void *data,
13 size_t data_size, off_t offset);
14 void explain_message_pread(char *message, int message_size, int fildes,
15 void *data, size_t data_size, off_t offset);
16 void explain_message_errno_pread(char *message, int message_size, int
17 errnum, int fildes, void *data, size_t data_size, off_t offset);
18
20 These functions may be used to obtain explanations for errors returned
21 by the pread(2) system call.
22 explain_pread
24 const char *explain_pread(int fildes, void *data, size_t data_size,
25 off_t offset);
26 The explain_pread function is used to obtain an explanation of an error
28 returned by the pread(2) system call. The least the message will con‐
29 tain is the value of strerror(errno), but usually it will do much bet‐
30 ter, and indicate the underlying cause in more detail.
31 The errno global variable will be used to obtain the error value to be
33 decoded.
34 fildes The original fildes, exactly as passed to the pread(2) system
36 call.
37 data The original data, exactly as passed to the pread(2) system
39 call.
40 data_size
42 The original data_size, exactly as passed to the pread(2) sys‐
43 tem call.
44 offset The original offset, exactly as passed to the pread(2) system
46 call.
47 Returns:
49 The message explaining the error. This message buffer is shared
50 by all libexplain functions which do not supply a buffer in
51 their argument list. This will be overwritten by the next call
52 to any libexplain function which shares this buffer, including
53 other threads.
54 Note: This function is not thread safe, because it shares a return buf‐
56 fer across all threads, and many other functions in this library.
57 Example: This function is intended to be used in a fashion similar to
59 the following example:
60 ssize_t result = pread(fildes, data, data_size, offset);
61 if (result < 0)
62 {
63 fprintf(stderr, "%s\n", explain_pread(fildes, data,
64 data_size, offset));
65 exit(EXIT_FAILURE);
66 }
67 The above code example is available pre‐packaged as the
69 explain_pread_or_die(3) function.
70 explain_errno_pread
72 const char *explain_errno_pread(int errnum, int fildes, void *data,
73 size_t data_size, off_t offset);
74 The explain_errno_pread function is used to obtain an explanation of an
76 error returned by the pread(2) system call. The least the message will
77 contain is the value of strerror(errno), but usually it will do much
78 better, and indicate the underlying cause in more detail.
79 errnum The error value to be decoded, usually obtained from the errno
81 global variable just before this function is called. This is
82 necessary if you need to call any code between the system call
83 to be explained and this function, because many libc functions
84 will alter the value of errno.
85 fildes The original fildes, exactly as passed to the pread(2) system
87 call.
88 data The original data, exactly as passed to the pread(2) system
90 call.
91 data_size
93 The original data_size, exactly as passed to the pread(2) sys‐
94 tem call.
95 offset The original offset, exactly as passed to the pread(2) system
97 call.
98 Returns:
100 The message explaining the error. This message buffer is shared
101 by all libexplain functions which do not supply a buffer in
102 their argument list. This will be overwritten by the next call
103 to any libexplain function which shares this buffer, including
104 other threads.
105 Note: This function is not thread safe, because it shares a return buf‐
107 fer across all threads, and many other functions in this library.
108 Example: This function is intended to be used in a fashion similar to
110 the following example:
111 ssize_t result = pread(fildes, data, data_size, offset);
112 if (result < 0)
113 {
114 int err = errno;
115 fprintf(stderr, "%s\n", explain_errno_pread(err, fildes,
116 data, data_size, offset));
117 exit(EXIT_FAILURE);
118 }
119 The above code example is available pre‐packaged as the
121 explain_pread_or_die(3) function.
122 explain_message_pread
124 void explain_message_pread(char *message, int message_size, int fildes,
125 void *data, size_t data_size, off_t offset);
126 The explain_message_pread function is used to obtain an explanation of
128 an error returned by the pread(2) system call. The least the message
129 will contain is the value of strerror(errno), but usually it will do
130 much better, and indicate the underlying cause in more detail.
131 The errno global variable will be used to obtain the error value to be
133 decoded.
134 message The location in which to store the returned message. If a suit‐
136 able message return buffer is supplied, this function is thread
137 safe.
138 message_size
140 The size in bytes of the location in which to store the
141 returned message.
142 fildes The original fildes, exactly as passed to the pread(2) system
144 call.
145 data The original data, exactly as passed to the pread(2) system
147 call.
148 data_size
150 The original data_size, exactly as passed to the pread(2) sys‐
151 tem call.
152 offset The original offset, exactly as passed to the pread(2) system
154 call.
155 Example: This function is intended to be used in a fashion similar to
157 the following example:
158 ssize_t result = pread(fildes, data, data_size, offset);
159 if (result < 0)
160 {
161 char message[3000];
162 explain_message_pread(message, sizeof(message), fildes,
163 data, data_size, offset);
164 fprintf(stderr, "%s\n", message);
165 exit(EXIT_FAILURE);
166 }
167 The above code example is available pre‐packaged as the
169 explain_pread_or_die(3) function.
170 explain_message_errno_pread
172 void explain_message_errno_pread(char *message, int message_size, int
173 errnum, int fildes, void *data, size_t data_size, off_t offset);
174 The explain_message_errno_pread function is used to obtain an explana‐
176 tion of an error returned by the pread(2) system call. The least the
177 message will contain is the value of strerror(errno), but usually it
178 will do much better, and indicate the underlying cause in more detail.
179 message The location in which to store the returned message. If a suit‐
181 able message return buffer is supplied, this function is thread
182 safe.
183 message_size
185 The size in bytes of the location in which to store the
186 returned message.
187 errnum The error value to be decoded, usually obtained from the errno
189 global variable just before this function is called. This is
190 necessary if you need to call any code between the system call
191 to be explained and this function, because many libc functions
192 will alter the value of errno.
193 fildes The original fildes, exactly as passed to the pread(2) system
195 call.
196 data The original data, exactly as passed to the pread(2) system
198 call.
199 data_size
201 The original data_size, exactly as passed to the pread(2) sys‐
202 tem call.
203 offset The original offset, exactly as passed to the pread(2) system
205 call.
206 Example: This function is intended to be used in a fashion similar to
208 the following example:
209 ssize_t result = pread(fildes, data, data_size, offset);
210 if (result < 0)
211 {
212 int err = errno;
213 char message[3000];
214 explain_message_errno_pread(message, sizeof(message), err,
215 fildes, data, data_size, offset);
216 fprintf(stderr, "%s\n", message);
217 exit(EXIT_FAILURE);
218 }
219 The above code example is available pre‐packaged as the
221 explain_pread_or_die(3) function.
222
224 pread(2)
225 read from or write to a file descriptor at a given offset
226 explain_pread_or_die(3)
228 read from or write to a file descriptor at a given offset and
229 report errors
230
232 libexplain version 0.40
233 Copyright (C) 2009 Peter Miller
234 explain_pread(3)