100 lines
3.9 KiB
C
100 lines
3.9 KiB
C
#ifndef __BITS_TYPES_FILE_H__
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# define __BITS_TYPES_FILE_H__
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#include <stddef.h>
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#include <stdint.h>
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#include <sys/types.h>
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#define __FILE_BUF_READ 0
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#define __FILE_BUF_WRITE 1
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/* The FILE structure is mostly a buffer around kernel-level I/O. Most of the
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work is maintaining that buffer to provide the basic fgetc()/fputc()
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functions, then everything else is built on top of the abstracted stream.
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The buffer of a FILE can either be in reading or writing mode. When in
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reading mode, the buffer contains pre-fetched data from a previous read that
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hasn't yet been requested by the user. When in writing mode, the buffer
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contains data written by the user which hasn't yet been sent to the kernel.
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The buffer has the following structure:
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0 bufpos bufread bufsize
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+--------+---------+---------+
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|xxxxxxxx|rrrrrrrrr|uuuuuuuuu| (When reading)
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+--------+---------+---------+
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|wwwwwwww|uuuuuuuuuuuuuuuuuuu| (When writing)
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+--------+-------------------+
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x: Data read from file descriptor and returned to user
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r: Data read from file descriptor not yet returned to user
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w: Data written by user not yet sent to file descriptor
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u: Undefined
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In reading mode, the region [0..bufread) contains data obtained from the
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file. bufpos marks how much has been read, in the sense that [0..bufpos) has
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already been returned to the user while [bufpos..bufread) has not. The offset
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on the underlying file descriptor sits at bufread, so the position reported
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by ftell() is fdpos - bufread + bufpos. The rest of the buffer is undefined.
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In writing mode, the region [0..bufpos) contains data received through API
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but not yet written to the file descriptor. ftell() reports fdpos + bufpos.
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The rest of the buffer is undefined.
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The ungetc() function pushes back characters into the buffer; if the FILE is
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unbuffered, then it's made buffered temporarily to hold the characters and
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cleared at the next fflush() or read. The buffer is put in reading mode. For
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this reason, reading functions should test [fp->buf] to check whether there
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is a buffer instead of [fp->bufmode != _IONBF].
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Many fields in the FILE structure are abstracted away by API calls in layers:
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1. [fd], [fdpos] and [error] are updated by the primitive functions of
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fileutil.c which essentially wrap kernel I/O (plus clearerr() obviously).
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2. [buf], [bufsize], [bufmode] and [bufowned] are handled by setbuf(),
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setvbuf() and fclose().
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3. [bufpos], [bufread] and [bufdir] are set by primitive read/write functions
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like fgets() or fwrite(), and cleared by fflush().
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4. [readable], [writable], [append] and [text] are set by fopen() and
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freopen(), and used as read-only by the primitive functions of 3.
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TODO: EOF indicator */
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typedef struct {
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/* File descriptor */
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int fd;
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/* Current position in file, as tracked by the file descriptor (ie. not
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accounting for buffer operations) */
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size_t fdpos;
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/* Pointer to buffer (NULL if _IONBF) */
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char *buf;
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/* Current position in buffer, water mark of read data in buffer, and
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buffer size; see header comment for details */
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size_t bufpos;
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size_t bufread;
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size_t bufsize;
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/* Number of ungetc()'d characters at the start of buffer data */
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int bufungetc;
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/* Buffering mode; one of _IOFBF, _IOLBF, or _IONBF */
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uint8_t bufmode :2;
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/* We own the buffer and it needs to be freed */
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uint8_t bufowned :1;
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/* __FILE_BUF_READ if the buffer is in reading mode
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__FILE_BUF_WRITE if it's in writing mode
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This mode can only be changed immediately after fflush(). */
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uint8_t bufdir :1;
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/* Opening flags */
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uint8_t readable :1;
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uint8_t writable :1;
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uint8_t append :1;
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/* Non-zero if text mode, zero if binary mode */
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uint8_t text :1;
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/* EOF indicator */
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uint8_t eof :1;
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/* Error indicator */
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uint8_t error :1;
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} FILE;
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#endif /*__BITS_TYPES_FILE_H__*/
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