diff options
Diffstat (limited to 'libio/fileops.c')
| -rw-r--r-- | libio/fileops.c | 102 |
1 files changed, 37 insertions, 65 deletions
diff --git a/libio/fileops.c b/libio/fileops.c index 2e7bc8dad9..cf68dbfe52 100644 --- a/libio/fileops.c +++ b/libio/fileops.c @@ -232,13 +232,18 @@ _IO_file_open (fp, filename, posix_mode, prot, read_write, is32not64) return NULL; fp->_fileno = fdesc; _IO_mask_flags (fp, read_write,_IO_NO_READS+_IO_NO_WRITES+_IO_IS_APPENDING); - if ((read_write & _IO_IS_APPENDING) && (read_write & _IO_NO_READS)) - if (_IO_SEEKOFF (fp, (_IO_off64_t)0, _IO_seek_end, _IOS_INPUT|_IOS_OUTPUT) - == _IO_pos_BAD && errno != ESPIPE) - { - close_not_cancel (fdesc); - return NULL; - } + /* For append mode, send the file offset to the end of the file. Don't + update the offset cache though, since the file handle is not active. */ + if ((read_write & (_IO_IS_APPENDING | _IO_NO_READS)) + == (_IO_IS_APPENDING | _IO_NO_READS)) + { + _IO_off64_t new_pos = _IO_SYSSEEK (fp, 0, _IO_seek_end); + if (new_pos == _IO_pos_BAD && errno != ESPIPE) + { + close_not_cancel (fdesc); + return NULL; + } + } _IO_link_in ((struct _IO_FILE_plus *) fp); return fp; } @@ -929,43 +934,13 @@ _IO_file_sync_mmap (_IO_FILE *fp) return 0; } -/* Get the current file offset using a system call. This is the safest method - to get the current file offset, since we are sure that we get the current - state of the file. Before the stream handle is activated (by using fread, - fwrite, etc.), an application may alter the state of the file descriptor - underlying it by calling read/write/lseek on it. Using a cached offset at - this point will result in returning the incorrect value. Same is the case - when one switches from reading in a+ mode to writing, where the buffer has - not been flushed - the cached offset would reflect the reading position - while the actual write position would be at the end of the file. - - do_ftell and do_ftell_wide may resort to using the cached offset in some - special cases instead of calling get_file_offset, but those cases should be - thoroughly described. */ -_IO_off64_t -get_file_offset (_IO_FILE *fp) -{ - if ((fp->_flags & _IO_IS_APPENDING) == _IO_IS_APPENDING) - { - struct stat64 st; - bool ret = (_IO_SYSSTAT (fp, &st) == 0 && S_ISREG (st.st_mode)); - if (ret) - return st.st_size; - else - return EOF; - } - else - return _IO_SYSSEEK (fp, 0, _IO_seek_cur); -} - - -/* ftell{,o} implementation. Don't modify any state of the file pointer while - we try to get the current state of the stream. */ +/* ftell{,o} implementation. The only time we modify the state of the stream + is when we have unflushed writes. In that case we seek to the end and + record that offset in the stream object. */ static _IO_off64_t do_ftell (_IO_FILE *fp) { - _IO_off64_t result = 0; - bool use_cached_offset = false; + _IO_off64_t result, offset = 0; /* No point looking at unflushed data if we haven't allocated buffers yet. */ @@ -974,39 +949,37 @@ do_ftell (_IO_FILE *fp) bool was_writing = (fp->_IO_write_ptr > fp->_IO_write_base || _IO_in_put_mode (fp)); + bool append_mode = (fp->_flags & _IO_IS_APPENDING) == _IO_IS_APPENDING; + + /* When we have unflushed writes in append mode, seek to the end of the + file and record that offset. This is the only time we change the file + stream state and it is safe since the file handle is active. */ + if (was_writing && append_mode) + { + result = _IO_SYSSEEK (fp, 0, _IO_seek_end); + if (result == _IO_pos_BAD) + return EOF; + else + fp->_offset = result; + } + /* Adjust for unflushed data. */ if (!was_writing) - result -= fp->_IO_read_end - fp->_IO_read_ptr; + offset -= fp->_IO_read_end - fp->_IO_read_ptr; else - result += fp->_IO_write_ptr - fp->_IO_read_end; - - /* It is safe to use the cached offset when available if there is - unbuffered data (indicating that the file handle is active) and the - handle is not for a file open in a+ mode. The latter condition is - because there could be a scenario where there is a switch from read - mode to write mode using an fseek to an arbitrary position. In this - case, there would be unbuffered data due to be appended to the end of - the file, but the offset may not necessarily be the end of the - file. It is fine to use the cached offset when the a+ stream is in - read mode though, since the offset is maintained correctly in that - case. Note that this is not a comprehensive set of cases when the - offset is reliable. The offset may be reliable even in some cases - where there is no unflushed input and the handle is active, but it's - just that we don't have a way to identify that condition reliably. */ - use_cached_offset = (result != 0 && fp->_offset != _IO_pos_BAD - && ((fp->_flags & (_IO_IS_APPENDING | _IO_NO_READS)) - == (_IO_IS_APPENDING | _IO_NO_READS) - && was_writing)); + offset += fp->_IO_write_ptr - fp->_IO_read_end; } - if (use_cached_offset) - result += fp->_offset; + if (fp->_offset != _IO_pos_BAD) + result = fp->_offset; else - result += get_file_offset (fp); + result = _IO_SYSSEEK (fp, 0, _IO_seek_cur); if (result == EOF) return result; + result += offset; + if (result < 0) { __set_errno (EINVAL); @@ -1016,7 +989,6 @@ do_ftell (_IO_FILE *fp) return result; } - _IO_off64_t _IO_new_file_seekoff (fp, offset, dir, mode) _IO_FILE *fp; |