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Diffstat (limited to '')
| -rw-r--r-- | lib/fflush.c | 232 |
1 files changed, 232 insertions, 0 deletions
diff --git a/lib/fflush.c b/lib/fflush.c new file mode 100644 index 0000000..a140b7a --- /dev/null +++ b/lib/fflush.c @@ -0,0 +1,232 @@ +/* fflush.c -- allow flushing input streams + Copyright (C) 2007-2018 Free Software Foundation, Inc. + + This program is free software: you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; either version 3 of the License, or + (at your option) any later version. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License + along with this program. If not, see <https://www.gnu.org/licenses/>. */ + +/* Written by Eric Blake. */ + +#include <config.h> + +/* Specification. */ +#include <stdio.h> + +#include <errno.h> +#include <unistd.h> + +#include "freading.h" + +#include "stdio-impl.h" + +#include "unused-parameter.h" + +#undef fflush + + +#if defined _IO_EOF_SEEN || defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1 +/* GNU libc, BeOS, Haiku, Linux libc5 */ + +/* Clear the stream's ungetc buffer, preserving the value of ftello (fp). */ +static void +clear_ungetc_buffer_preserving_position (FILE *fp) +{ + if (fp->_flags & _IO_IN_BACKUP) + /* _IO_free_backup_area is a bit complicated. Simply call fseek. */ + fseeko (fp, 0, SEEK_CUR); +} + +#else + +/* Clear the stream's ungetc buffer. May modify the value of ftello (fp). */ +static void +clear_ungetc_buffer (FILE *fp) +{ +# if defined __sferror || defined __DragonFly__ || defined __ANDROID__ + /* FreeBSD, NetBSD, OpenBSD, DragonFly, Mac OS X, Cygwin, Minix 3, Android */ + if (HASUB (fp)) + { + fp_->_p += fp_->_r; + fp_->_r = 0; + } +# elif defined __EMX__ /* emx+gcc */ + if (fp->_ungetc_count > 0) + { + fp->_ungetc_count = 0; + fp->_rcount = - fp->_rcount; + } +# elif defined _IOERR /* Minix, AIX, HP-UX, IRIX, OSF/1, Solaris, OpenServer, mingw, MSVC, NonStop Kernel, OpenVMS */ + /* Nothing to do. */ +# else /* other implementations */ + fseeko (fp, 0, SEEK_CUR); +# endif +} + +#endif + +#if ! (defined _IO_EOF_SEEN || defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1) +/* GNU libc, BeOS, Haiku, Linux libc5 */ + +# if (defined __sferror || defined __DragonFly__ || defined __ANDROID__) && defined __SNPT +/* FreeBSD, NetBSD, OpenBSD, DragonFly, Mac OS X, Cygwin, Minix 3, Android */ + +static int +disable_seek_optimization (FILE *fp) +{ + int saved_flags = fp_->_flags & (__SOPT | __SNPT); + fp_->_flags = (fp_->_flags & ~__SOPT) | __SNPT; + return saved_flags; +} + +static void +restore_seek_optimization (FILE *fp, int saved_flags) +{ + fp_->_flags = (fp_->_flags & ~(__SOPT | __SNPT)) | saved_flags; +} + +# else + +static void +update_fpos_cache (FILE *fp _GL_UNUSED_PARAMETER, + off_t pos _GL_UNUSED_PARAMETER) +{ +# if defined __sferror || defined __DragonFly__ || defined __ANDROID__ + /* FreeBSD, NetBSD, OpenBSD, DragonFly, Mac OS X, Cygwin, Minix 3, Android */ +# if defined __CYGWIN__ + /* fp_->_offset is typed as an integer. */ + fp_->_offset = pos; +# else + /* fp_->_offset is an fpos_t. */ + /* Use a union, since on NetBSD, the compilation flags determine + whether fpos_t is typedef'd to off_t or a struct containing a + single off_t member. */ + union + { + fpos_t f; + off_t o; + } u; + u.o = pos; + fp_->_offset = u.f; +# endif + fp_->_flags |= __SOFF; +# endif +} +# endif +#endif + +/* Flush all pending data on STREAM according to POSIX rules. Both + output and seekable input streams are supported. */ +int +rpl_fflush (FILE *stream) +{ + /* When stream is NULL, POSIX and C99 only require flushing of "output + streams and update streams in which the most recent operation was not + input", and all implementations do this. + + When stream is "an output stream or an update stream in which the most + recent operation was not input", POSIX and C99 requires that fflush + writes out any buffered data, and all implementations do this. + + When stream is, however, an input stream or an update stream in + which the most recent operation was input, C99 specifies nothing, + and POSIX only specifies behavior if the stream is seekable. + mingw, in particular, drops the input buffer, leaving the file + descriptor positioned at the end of the input buffer. I.e. ftell + (stream) is lost. We don't want to call the implementation's + fflush in this case. + + We test ! freading (stream) here, rather than fwriting (stream), because + what we need to know is whether the stream holds a "read buffer", and on + mingw this is indicated by _IOREAD, regardless of _IOWRT. */ + if (stream == NULL || ! freading (stream)) + return fflush (stream); + +#if defined _IO_EOF_SEEN || defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1 + /* GNU libc, BeOS, Haiku, Linux libc5 */ + + clear_ungetc_buffer_preserving_position (stream); + + return fflush (stream); + +#else + { + /* Notes about the file-position indicator: + 1) The file position indicator is incremented by fgetc() and decremented + by ungetc(): + <http://www.opengroup.org/susv3/functions/fgetc.html> + "... the fgetc() function shall ... advance the associated file + position indicator for the stream ..." + <http://www.opengroup.org/susv3/functions/ungetc.html> + "The file-position indicator is decremented by each successful + call to ungetc()..." + 2) <http://www.opengroup.org/susv3/functions/ungetc.html> says: + "The value of the file-position indicator for the stream after + reading or discarding all pushed-back bytes shall be the same + as it was before the bytes were pushed back." + Here we are discarding all pushed-back bytes. But more specifically, + 3) <http://www.opengroup.org/austin/aardvark/latest/xshbug3.txt> says: + "[After fflush(),] the file offset of the underlying open file + description shall be set to the file position of the stream, and + any characters pushed back onto the stream by ungetc() ... shall + be discarded." */ + + /* POSIX does not specify fflush behavior for non-seekable input + streams. Some implementations purge unread data, some return + EBADF, some do nothing. */ + off_t pos = ftello (stream); + if (pos == -1) + { + errno = EBADF; + return EOF; + } + + /* Clear the ungetc buffer. */ + clear_ungetc_buffer (stream); + + /* To get here, we must be flushing a seekable input stream, so the + semantics of fpurge are now appropriate to clear the buffer. To + avoid losing data, the lseek is also necessary. */ + { + int result = fpurge (stream); + if (result != 0) + return result; + } + +# if (defined __sferror || defined __DragonFly__ || defined __ANDROID__) && defined __SNPT + /* FreeBSD, NetBSD, OpenBSD, DragonFly, Mac OS X, Cygwin, Minix 3, Android */ + + { + /* Disable seek optimization for the next fseeko call. This tells the + following fseeko call to seek to the desired position directly, rather + than to seek to a block-aligned boundary. */ + int saved_flags = disable_seek_optimization (stream); + int result = fseeko (stream, pos, SEEK_SET); + + restore_seek_optimization (stream, saved_flags); + return result; + } + +# else + + pos = lseek (fileno (stream), pos, SEEK_SET); + if (pos == -1) + return EOF; + /* After a successful lseek, update the file descriptor's position cache + in the stream. */ + update_fpos_cache (stream, pos); + + return 0; + +# endif + } +#endif +} |