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1 | /* fflush.c -- allow flushing input streams |
2 | Copyright (C) 2007-2011 Free Software Foundation, Inc. | |
3 | ||
4 | This program is free software: you can redistribute it and/or modify | |
5 | it under the terms of the GNU Lesser General Public License as published by | |
6 | the Free Software Foundation; either version 3 of the License, or | |
7 | (at your option) any later version. | |
8 | ||
9 | This program is distributed in the hope that it will be useful, | |
10 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
11 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
12 | GNU Lesser General Public License for more details. | |
13 | ||
14 | You should have received a copy of the GNU Lesser General Public License | |
15 | along with this program. If not, see <http://www.gnu.org/licenses/>. */ | |
16 | ||
17 | /* Written by Eric Blake. */ | |
18 | ||
19 | #include <config.h> | |
20 | ||
21 | /* Specification. */ | |
22 | #include <stdio.h> | |
23 | ||
24 | #include <errno.h> | |
25 | #include <unistd.h> | |
26 | ||
27 | #include "freading.h" | |
28 | ||
29 | #include "stdio-impl.h" | |
30 | ||
31 | #undef fflush | |
32 | ||
33 | ||
34 | #if defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */ | |
35 | ||
36 | /* Clear the stream's ungetc buffer, preserving the value of ftello (fp). */ | |
37 | static inline void | |
38 | clear_ungetc_buffer_preserving_position (FILE *fp) | |
39 | { | |
40 | if (fp->_flags & _IO_IN_BACKUP) | |
41 | /* _IO_free_backup_area is a bit complicated. Simply call fseek. */ | |
42 | fseeko (fp, 0, SEEK_CUR); | |
43 | } | |
44 | ||
45 | #else | |
46 | ||
47 | /* Clear the stream's ungetc buffer. May modify the value of ftello (fp). */ | |
48 | static inline void | |
49 | clear_ungetc_buffer (FILE *fp) | |
50 | { | |
51 | # if defined __sferror || defined __DragonFly__ /* FreeBSD, NetBSD, OpenBSD, DragonFly, MacOS X, Cygwin */ | |
52 | if (HASUB (fp)) | |
53 | { | |
54 | fp_->_p += fp_->_r; | |
55 | fp_->_r = 0; | |
56 | } | |
57 | # elif defined __EMX__ /* emx+gcc */ | |
58 | if (fp->_ungetc_count > 0) | |
59 | { | |
60 | fp->_ungetc_count = 0; | |
61 | fp->_rcount = - fp->_rcount; | |
62 | } | |
63 | # elif defined _IOERR /* AIX, HP-UX, IRIX, OSF/1, Solaris, OpenServer, mingw, NonStop Kernel */ | |
64 | /* Nothing to do. */ | |
65 | # else /* other implementations */ | |
66 | fseeko (fp, 0, SEEK_CUR); | |
67 | # endif | |
68 | } | |
69 | ||
70 | #endif | |
71 | ||
72 | #if (defined __sferror || defined __DragonFly__) && defined __SNPT /* FreeBSD, NetBSD, OpenBSD, DragonFly, MacOS X, Cygwin */ | |
73 | ||
74 | static inline int | |
75 | disable_seek_optimization (FILE *fp) | |
76 | { | |
77 | int saved_flags = fp_->_flags & (__SOPT | __SNPT); | |
78 | fp_->_flags = (fp_->_flags & ~__SOPT) | __SNPT; | |
79 | return saved_flags; | |
80 | } | |
81 | ||
82 | static inline void | |
83 | restore_seek_optimization (FILE *fp, int saved_flags) | |
84 | { | |
85 | fp_->_flags = (fp_->_flags & ~(__SOPT | __SNPT)) | saved_flags; | |
86 | } | |
87 | ||
88 | #endif | |
89 | ||
90 | static inline void | |
91 | update_fpos_cache (FILE *fp, off_t pos) | |
92 | { | |
93 | #if defined __sferror || defined __DragonFly__ /* FreeBSD, NetBSD, OpenBSD, DragonFly, MacOS X, Cygwin */ | |
94 | # if defined __CYGWIN__ | |
95 | /* fp_->_offset is typed as an integer. */ | |
96 | fp_->_offset = pos; | |
97 | # else | |
98 | /* fp_->_offset is an fpos_t. */ | |
99 | /* Use a union, since on NetBSD, the compilation flags determine | |
100 | whether fpos_t is typedef'd to off_t or a struct containing a | |
101 | single off_t member. */ | |
102 | union | |
103 | { | |
104 | fpos_t f; | |
105 | off_t o; | |
106 | } u; | |
107 | u.o = pos; | |
108 | fp_->_offset = u.f; | |
109 | # endif | |
110 | fp_->_flags |= __SOFF; | |
111 | #endif | |
112 | } | |
113 | ||
114 | /* Flush all pending data on STREAM according to POSIX rules. Both | |
115 | output and seekable input streams are supported. */ | |
116 | int | |
117 | rpl_fflush (FILE *stream) | |
118 | { | |
119 | /* When stream is NULL, POSIX and C99 only require flushing of "output | |
120 | streams and update streams in which the most recent operation was not | |
121 | input", and all implementations do this. | |
122 | ||
123 | When stream is "an output stream or an update stream in which the most | |
124 | recent operation was not input", POSIX and C99 requires that fflush | |
125 | writes out any buffered data, and all implementations do this. | |
126 | ||
127 | When stream is, however, an input stream or an update stream in | |
128 | which the most recent operation was input, C99 specifies nothing, | |
129 | and POSIX only specifies behavior if the stream is seekable. | |
130 | mingw, in particular, drops the input buffer, leaving the file | |
131 | descriptor positioned at the end of the input buffer. I.e. ftell | |
132 | (stream) is lost. We don't want to call the implementation's | |
133 | fflush in this case. | |
134 | ||
135 | We test ! freading (stream) here, rather than fwriting (stream), because | |
136 | what we need to know is whether the stream holds a "read buffer", and on | |
137 | mingw this is indicated by _IOREAD, regardless of _IOWRT. */ | |
138 | if (stream == NULL || ! freading (stream)) | |
139 | return fflush (stream); | |
140 | ||
141 | #if defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */ | |
142 | ||
143 | clear_ungetc_buffer_preserving_position (stream); | |
144 | ||
145 | return fflush (stream); | |
146 | ||
147 | #else | |
148 | { | |
149 | /* Notes about the file-position indicator: | |
150 | 1) The file position indicator is incremented by fgetc() and decremented | |
151 | by ungetc(): | |
152 | <http://www.opengroup.org/susv3/functions/fgetc.html> | |
153 | "... the fgetc() function shall ... advance the associated file | |
154 | position indicator for the stream ..." | |
155 | <http://www.opengroup.org/susv3/functions/ungetc.html> | |
156 | "The file-position indicator is decremented by each successful | |
157 | call to ungetc()..." | |
158 | 2) <http://www.opengroup.org/susv3/functions/ungetc.html> says: | |
159 | "The value of the file-position indicator for the stream after | |
160 | reading or discarding all pushed-back bytes shall be the same | |
161 | as it was before the bytes were pushed back." | |
162 | Here we are discarding all pushed-back bytes. But more specifically, | |
163 | 3) <http://www.opengroup.org/austin/aardvark/latest/xshbug3.txt> says: | |
164 | "[After fflush(),] the file offset of the underlying open file | |
165 | description shall be set to the file position of the stream, and | |
166 | any characters pushed back onto the stream by ungetc() ... shall | |
167 | be discarded." */ | |
168 | ||
169 | /* POSIX does not specify fflush behavior for non-seekable input | |
170 | streams. Some implementations purge unread data, some return | |
171 | EBADF, some do nothing. */ | |
172 | off_t pos = ftello (stream); | |
173 | if (pos == -1) | |
174 | { | |
175 | errno = EBADF; | |
176 | return EOF; | |
177 | } | |
178 | ||
179 | /* Clear the ungetc buffer. */ | |
180 | clear_ungetc_buffer (stream); | |
181 | ||
182 | /* To get here, we must be flushing a seekable input stream, so the | |
183 | semantics of fpurge are now appropriate to clear the buffer. To | |
184 | avoid losing data, the lseek is also necessary. */ | |
185 | { | |
186 | int result = fpurge (stream); | |
187 | if (result != 0) | |
188 | return result; | |
189 | } | |
190 | ||
191 | # if (defined __sferror || defined __DragonFly__) && defined __SNPT /* FreeBSD, NetBSD, OpenBSD, DragonFly, MacOS X, Cygwin */ | |
192 | ||
193 | { | |
194 | /* Disable seek optimization for the next fseeko call. This tells the | |
195 | following fseeko call to seek to the desired position directly, rather | |
196 | than to seek to a block-aligned boundary. */ | |
197 | int saved_flags = disable_seek_optimization (stream); | |
198 | int result = fseeko (stream, pos, SEEK_SET); | |
199 | ||
200 | restore_seek_optimization (stream, saved_flags); | |
201 | return result; | |
202 | } | |
203 | ||
204 | # else | |
205 | ||
206 | pos = lseek (fileno (stream), pos, SEEK_SET); | |
207 | if (pos == -1) | |
208 | return EOF; | |
209 | /* After a successful lseek, update the file descriptor's position cache | |
210 | in the stream. */ | |
211 | update_fpos_cache (stream, pos); | |
212 | ||
213 | return 0; | |
214 | ||
215 | # endif | |
216 | } | |
217 | #endif | |
218 | } |