/* An fstream can be in at most one of put mode, get mode, or putback mode. Putback mode is a variant of get mode. In a filebuf, there is only one current position, instead of two separate get and put pointers. In get mode, the current position is that of gptr(); in put mode that of pptr(). The position in the buffer that corresponds to the position in external file system is normally _IO_read_end, except in putback mode, when it is _IO_save_end and also when the file is in append mode, since switching from read to write mode automatically sends the position in the external file system to the end of file. If the field _fb._offset is >= 0, it gives the offset in the file as a whole corresponding to eGptr(). (?) PUT MODE: If a filebuf is in put mode, then all of _IO_read_ptr, _IO_read_end, and _IO_read_base are equal to each other. These are usually equal to _IO_buf_base, though not necessarily if we have switched from get mode to put mode. (The reason is to maintain the invariant that _IO_read_end corresponds to the external file position.) _IO_write_base is non-NULL and usually equal to _IO_buf_base. We also have _IO_write_end == _IO_buf_end, but only in fully buffered mode. The un-flushed character are those between _IO_write_base and _IO_write_ptr. GET MODE: If a filebuf is in get or putback mode, eback() != egptr(). In get mode, the unread characters are between gptr() and egptr(). The OS file position corresponds to that of egptr(). PUTBACK MODE: Putback mode is used to remember "excess" characters that have been sputbackc'd in a separate putback buffer. In putback mode, the get buffer points to the special putback buffer. The unread characters are the characters between gptr() and egptr() in the putback buffer, as well as the area between save_gptr() and save_egptr(), which point into the original reserve buffer. (The pointers save_gptr() and save_egptr() are the values of gptr() and egptr() at the time putback mode was entered.) The OS position corresponds to that of save_egptr(). LINE BUFFERED OUTPUT: During line buffered output, _IO_write_base==base() && epptr()==base(). However, ptr() may be anywhere between base() and ebuf(). This forces a call to filebuf::overflow(int C) on every put. If there is more space in the buffer, and C is not a '\n', then C is inserted, and pptr() incremented. UNBUFFERED STREAMS: If a filebuf is unbuffered(), the _shortbuf[1] is used as the buffer. */
int _IO_new_file_overflow (FILE *f, int ch) { if (f->_flags & _IO_NO_WRITES) /* SET ERROR */ { f->_flags |= _IO_ERR_SEEN; __set_errno (EBADF); return EOF; } /* If currently reading or no buffer allocated. */ if ((f->_flags & _IO_CURRENTLY_PUTTING) == 0 || f->_IO_write_base == NULL) { /* Allocate a buffer if needed. */ if (f->_IO_write_base == NULL) { _IO_doallocbuf (f); _IO_setg (f, f->_IO_buf_base, f->_IO_buf_base, f->_IO_buf_base); } /* Otherwise must be currently reading. If _IO_read_ptr (and hence also _IO_read_end) is at the buffer end, logically slide the buffer forwards one block (by setting the read pointers to all point at the beginning of the block). This makes room for subsequent output. Otherwise, set the read pointers to _IO_read_end (leaving that alone, so it can continue to correspond to the external position). */ if (__glibc_unlikely (_IO_in_backup (f))) { size_t nbackup = f->_IO_read_end - f->_IO_read_ptr; _IO_free_backup_area (f); f->_IO_read_base -= MIN (nbackup, f->_IO_read_base - f->_IO_buf_base); f->_IO_read_ptr = f->_IO_read_base; }
if (fp->_IO_buf_base == NULL) { /* Maybe we already have a push back pointer. */ if (fp->_IO_save_base != NULL) { free (fp->_IO_save_base); fp->_flags &= ~_IO_IN_BACKUP; } _IO_doallocbuf (fp); }
/* FIXME This can/should be moved to genops ?? */ if (fp->_flags & (_IO_LINE_BUF|_IO_UNBUFFERED)) { /* We used to flush all line-buffered stream. This really isn't required by any standard. My recollection is that traditional Unix systems did this for stdout. stderr better not be line buffered. So we do just that here explicitly. --drepper */ _IO_acquire_lock (stdout);
/* This is very tricky. We have to adjust those pointers before we call _IO_SYSREAD () since we may longjump () out while waiting for input. Those pointers may be screwed up. H.J. */ fp->_IO_read_base = fp->_IO_read_ptr = fp->_IO_buf_base; fp->_IO_read_end = fp->_IO_buf_base; fp->_IO_write_base = fp->_IO_write_ptr = fp->_IO_write_end = fp->_IO_buf_base;
count = _IO_SYSREAD (fp, fp->_IO_buf_base, fp->_IO_buf_end - fp->_IO_buf_base);//注意读的大小是缓冲区的大小,这意味r-end可能会向后移动很多,从而导致读写不一致(_offset偏后) if (count <= 0) { if (count == 0) fp->_flags |= _IO_EOF_SEEN; else fp->_flags |= _IO_ERR_SEEN, count = 0; } fp->_IO_read_end += count; if (count == 0) { /* If a stream is read to EOF, the calling application may switch active handles. As a result, our offset cache would no longer be valid, so unset it. */ fp->_offset = _IO_pos_BAD; return EOF; } if (fp->_offset != _IO_pos_BAD) _IO_pos_adjust (fp->_offset, count); return *(unsignedchar *) fp->_IO_read_ptr; } libc_hidden_ver (_IO_new_file_underflow, _IO_file_underflow)
off64_t _IO_new_file_seekoff (FILE *fp, off64_t offset, int dir, int mode) { off64_t result; off64_t delta, new_offset; long count;
/* Short-circuit into a separate function. We don't want to mix any functionality and we don't want to touch anything inside the FILE object. */ if (mode == 0) return do_ftell (fp);
/* POSIX.1 8.2.3.7 says that after a call the fflush() the file offset of the underlying file must be exact. */ int must_be_exact = (fp->_IO_read_base == fp->_IO_read_end && fp->_IO_write_base == fp->_IO_write_ptr);
/* Flush unwritten characters. (This may do an unneeded write if we seek within the buffer. But to be able to switch to reading, we would need to set egptr to pptr. That can't be done in the current design, which assumes file_ptr() is eGptr. Anyway, since we probably end up flushing when we close(), it doesn't make much difference.) FIXME: simulate mem-mapped files. */ if (was_writing && _IO_switch_to_get_mode (fp)) return EOF;
if (fp->_IO_buf_base == NULL) { /* It could be that we already have a pushback buffer. */ if (fp->_IO_read_base != NULL) { free (fp->_IO_read_base); fp->_flags &= ~_IO_IN_BACKUP; } _IO_doallocbuf (fp); _IO_setp (fp, fp->_IO_buf_base, fp->_IO_buf_base); _IO_setg (fp, fp->_IO_buf_base, fp->_IO_buf_base, fp->_IO_buf_base); }
switch (dir) { case _IO_seek_cur: /* Adjust for read-ahead (bytes is buffer). */ offset -= fp->_IO_read_end - fp->_IO_read_ptr;
if (fp->_offset == _IO_pos_BAD) goto dumb; /* Make offset absolute, assuming current pointer is file_ptr(). */ offset += fp->_offset; if (offset < 0) { __set_errno (EINVAL); return EOF; }
dir = _IO_seek_set; break; case _IO_seek_set: break; case _IO_seek_end: { structstat64st; if (_IO_SYSSTAT (fp, &st) == 0 && S_ISREG (st.st_mode)) { offset += st.st_size; dir = _IO_seek_set; } else goto dumb; } }
_IO_free_backup_area (fp);
/* At this point, dir==_IO_seek_set. */
/* If destination is within current buffer, optimize: */ if (fp->_offset != _IO_pos_BAD && fp->_IO_read_base != NULL && !_IO_in_backup (fp)) { off64_t start_offset = (fp->_offset - (fp->_IO_read_end - fp->_IO_buf_base)); if (offset >= start_offset && offset < fp->_offset) { _IO_setg (fp, fp->_IO_buf_base, fp->_IO_buf_base + (offset - start_offset), fp->_IO_read_end); _IO_setp (fp, fp->_IO_buf_base, fp->_IO_buf_base);
resync: /* We need to do it since it is possible that the file offset in the kernel may be changed behind our back. It may happen when we fopen a file and then do a fork. One process may access the file and the kernel file offset will be changed. */ if (fp->_offset >= 0) _IO_SYSSEEK (fp, fp->_offset, 0);
if (fp->_IO_buf_base == NULL) { /* Maybe we already have a push back pointer. */ if (fp->_IO_save_base != NULL) { free (fp->_IO_save_base); fp->_flags &= ~_IO_IN_BACKUP; } _IO_doallocbuf (fp); }
while (want > 0) { have = fp->_IO_read_end - fp->_IO_read_ptr; if (want <= have) { memcpy (s, fp->_IO_read_ptr, want); fp->_IO_read_ptr += want; want = 0; } else { if (have > 0) { s = __mempcpy (s, fp->_IO_read_ptr, have); want -= have; fp->_IO_read_ptr += have; }
/* Check for backup and repeat */ if (_IO_in_backup (fp)) { _IO_switch_to_main_get_area (fp); continue; }
/* If we now want less than a buffer, underflow and repeat the copy. Otherwise, _IO_SYSREAD directly to the user buffer. */ if (fp->_IO_buf_base && want < (size_t) (fp->_IO_buf_end - fp->_IO_buf_base)) { if (__underflow (fp) == EOF) break;
continue; }
/* These must be set before the sysread as we might longjmp out waiting for input. */ _IO_setg (fp, fp->_IO_buf_base, fp->_IO_buf_base, fp->_IO_buf_base); _IO_setp (fp, fp->_IO_buf_base, fp->_IO_buf_base);
/* Try to maintain alignment: read a whole number of blocks. */ count = want; if (fp->_IO_buf_base) { size_t block_size = fp->_IO_buf_end - fp->_IO_buf_base; if (block_size >= 128) count -= want % block_size; }
if (n <= 0) return0; /* This is an optimized implementation. If the amount to be written straddles a block boundary (or the filebuf is unbuffered), use sys_write directly. */
/* First figure out how much space is available in the buffer. */ if ((f->_flags & _IO_LINE_BUF) && (f->_flags & _IO_CURRENTLY_PUTTING)) { count = f->_IO_buf_end - f->_IO_write_ptr; if (count >= n) { constchar *p; for (p = s + n; p > s; ) { if (*--p == '\n') { count = p - s + 1; must_flush = 1; break; } } } } elseif (f->_IO_write_end > f->_IO_write_ptr) count = f->_IO_write_end - f->_IO_write_ptr; /* Space available. */
/* Then fill the buffer. */ if (count > 0) { if (count > to_do) count = to_do; f->_IO_write_ptr = __mempcpy (f->_IO_write_ptr, s, count); s += count; to_do -= count; } if (to_do + must_flush > 0) { size_t block_size, do_write; /* Next flush the (full) buffer. */ if (_IO_OVERFLOW (f, EOF) == EOF) /* If nothing else has to be written we must not signal the caller that everything has been written. */ return to_do == 0 ? EOF : n - to_do;
/* Try to maintain alignment: write a whole number of blocks. */ block_size = f->_IO_buf_end - f->_IO_buf_base; do_write = to_do - (block_size >= 128 ? to_do % block_size : 0);
if (do_write) { count = new_do_write (f, s, do_write); to_do -= count; if (count < do_write) return n - to_do;//绕过缓冲区 }
/* Now write out the remainder. Normally, this will fit in the buffer, but it's somewhat messier for line-buffered files, so we let _IO_default_xsputn handle the general case. */ if (to_do) to_do -= _IO_default_xsputn (f, s+do_write, to_do); } return n - to_do; } libc_hidden_ver (_IO_new_file_xsputn, _IO_file_xsputn)
