libc/stdio/fseek.c - platform/bionic - Git at Google

 /*	$OpenBSD: fseek.c,v 1.7 2005/08/08 08:05:36 espie Exp $ */
 /*-
  * Copyright (c) 1990, 1993
  *	The Regents of the University of California.  All rights reserved.
  *
  * This code is derived from software contributed to Berkeley by
  * Chris Torek.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  * 3. Neither the name of the University nor the names of its contributors
  *    may be used to endorse or promote products derived from this software
  *    without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */

 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <errno.h>
 #include "local.h"

 #define	POS_ERR	(-(fpos_t)1)

 /*
  * Seek the given file to the given offset.
  * `Whence' must be one of the three SEEK_* macros.
  */
 int
 fseeko(FILE *fp, off_t offset, int whence)
 {
 	fpos_t (*seekfn)(void *, fpos_t, int);
 	fpos_t target, curoff;
 	size_t n;
 	struct stat st;
 	int havepos;

 	/* make sure stdio is set up */
 	if (!__sdidinit)
 		__sinit();

 	/*
 	 * Have to be able to seek.
 	 */
 	if ((seekfn = fp->_seek) == NULL) {
 		errno = ESPIPE;			/* historic practice */
 		return (EOF);
 	}

 	/*
 	 * Change any SEEK_CUR to SEEK_SET, and check `whence' argument.
 	 * After this, whence is either SEEK_SET or SEEK_END.
 	 */
 	FLOCKFILE(fp);
 	switch (whence) {

 	case SEEK_CUR:
 		/*
 		 * In order to seek relative to the current stream offset,
 		 * we have to first find the current stream offset a la
 		 * ftell (see ftell for details).
 		 */
 		__sflush(fp);	/* may adjust seek offset on append stream */
 		if (fp->_flags & __SOFF)
 			curoff = fp->_offset;
 		else {
 			curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
 			if (curoff == (fpos_t)-1) {
 				FUNLOCKFILE(fp);
 				return (EOF);
 			}
 		}
 		if (fp->_flags & __SRD) {
 			curoff -= fp->_r;
 			if (HASUB(fp))
 				curoff -= fp->_ur;
 		} else if (fp->_flags & __SWR && fp->_p != NULL)
 			curoff += fp->_p - fp->_bf._base;

 		offset += curoff;
 		whence = SEEK_SET;
 		havepos = 1;
 		break;

 	case SEEK_SET:
 	case SEEK_END:
 		curoff = 0;		/* XXX just to keep gcc quiet */
 		havepos = 0;
 		break;

 	default:
 		FUNLOCKFILE(fp);
 		errno = EINVAL;
 		return (EOF);
 	}

 	/*
 	 * Can only optimise if:
 	 *	reading (and not reading-and-writing);
 	 *	not unbuffered; and
 	 *	this is a `regular' Unix file (and hence seekfn==__sseek).
 	 * We must check __NBF first, because it is possible to have __NBF
 	 * and __SOPT both set.
 	 */
 	if (fp->_bf._base == NULL)
 		__smakebuf(fp);
 	if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT))
 		goto dumb;
 	if ((fp->_flags & __SOPT) == 0) {
 		if (seekfn != __sseek ||
 		    fp->_file < 0 || fstat(fp->_file, &st) ||
 		    (st.st_mode & S_IFMT) != S_IFREG) {
 			fp->_flags |= __SNPT;
 			goto dumb;
 		}
 		fp->_blksize = st.st_blksize;
 		fp->_flags |= __SOPT;
 	}

 	/*
 	 * We are reading; we can try to optimise.
 	 * Figure out where we are going and where we are now.
 	 */
 	if (whence == SEEK_SET)
 		target = offset;
 	else {
 		if (fstat(fp->_file, &st))
 			goto dumb;
 		target = st.st_size + offset;
 	}

 	if (!havepos) {
 		if (fp->_flags & __SOFF)
 			curoff = fp->_offset;
 		else {
 			curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
 			if (curoff == POS_ERR)
 				goto dumb;
 		}
 		curoff -= fp->_r;
 		if (HASUB(fp))
 			curoff -= fp->_ur;
 	}

 	/*
 	 * Compute the number of bytes in the input buffer (pretending
 	 * that any ungetc() input has been discarded).  Adjust current
 	 * offset backwards by this count so that it represents the
 	 * file offset for the first byte in the current input buffer.
 	 */
 	if (HASUB(fp)) {
 		curoff += fp->_r;	/* kill off ungetc */
 		n = fp->_up - fp->_bf._base;
 		curoff -= n;
 		n += fp->_ur;
 	} else {
 		n = fp->_p - fp->_bf._base;
 		curoff -= n;
 		n += fp->_r;
 	}

 	/*
 	 * If the target offset is within the current buffer,
 	 * simply adjust the pointers, clear EOF, undo ungetc(),
 	 * and return.  (If the buffer was modified, we have to
 	 * skip this; see fgetln.c.)
 	 */
 	if ((fp->_flags & __SMOD) == 0 &&
 	    target >= curoff && target < (fpos_t)(curoff + n)) {
 		int o = target - curoff;

 		fp->_p = fp->_bf._base + o;
 		fp->_r = n - o;
 		if (HASUB(fp))
 			FREEUB(fp);
 		fp->_flags &= ~__SEOF;
 		FUNLOCKFILE(fp);
 		return (0);
 	}

 	/*
 	 * The place we want to get to is not within the current buffer,
 	 * but we can still be kind to the kernel copyout mechanism.
 	 * By aligning the file offset to a block boundary, we can let
 	 * the kernel use the VM hardware to map pages instead of
 	 * copying bytes laboriously.  Using a block boundary also
 	 * ensures that we only read one block, rather than two.
 	 */
 	curoff = target & ~(fp->_blksize - 1);
 	if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR)
 		goto dumb;
 	fp->_r = 0;
 	fp->_p = fp->_bf._base;
 	if (HASUB(fp))
 		FREEUB(fp);
 	fp->_flags &= ~__SEOF;
 	n = target - curoff;
 	if (n) {
 		if (__srefill(fp) || (size_t)fp->_r < n)
 			goto dumb;
 		fp->_p += n;
 		fp->_r -= n;
 	}
 	FUNLOCKFILE(fp);
 	return (0);

 	/*
 	 * We get here if we cannot optimise the seek ... just
 	 * do it.  Allow the seek function to change fp->_bf._base.
 	 */
 dumb:
 	if (__sflush(fp) ||
 	    (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) {
 		FUNLOCKFILE(fp);
 		return (EOF);
 	}
 	/* success: clear EOF indicator and discard ungetc() data */
 	if (HASUB(fp))
 		FREEUB(fp);
 	fp->_p = fp->_bf._base;
 	fp->_r = 0;
 	/* fp->_w = 0; */	/* unnecessary (I think...) */
 	fp->_flags &= ~__SEOF;
 	FUNLOCKFILE(fp);
 	return (0);
 }

 /*
  * fseek()'s offset is a long and sizeof(off_t) != sizeof(long) on all arches
  */
 #if defined(__alpha__) && defined(__indr_reference)
 __indr_reference(fseeko, fseek);
 #else
 int
 fseek(FILE *fp, long offset, int whence)
 {
 	off_t off = offset;

 	return(fseeko(fp, off, whence));
 }
 #endif
	/* $OpenBSD: fseek.c,v 1.7 2005/08/08 08:05:36 espie Exp $ */
	/*-
	* Copyright (c) 1990, 1993
	* The Regents of the University of California. All rights reserved.
	*
	* This code is derived from software contributed to Berkeley by
	* Chris Torek.
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions
	* are met:
	* 1. Redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer.
	* 2. Redistributions in binary form must reproduce the above copyright
	* notice, this list of conditions and the following disclaimer in the
	* documentation and/or other materials provided with the distribution.
	* 3. Neither the name of the University nor the names of its contributors
	* may be used to endorse or promote products derived from this software
	* without specific prior written permission.
	*
	* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	* SUCH DAMAGE.
	*/

	#include <sys/types.h>
	#include <sys/stat.h>
	#include <fcntl.h>
	#include <stdio.h>
	#include <stdlib.h>
	#include <errno.h>
	#include "local.h"

	#define POS_ERR (-(fpos_t)1)

	/*
	* Seek the given file to the given offset.
	* `Whence' must be one of the three SEEK_* macros.
	*/
	int
	fseeko(FILE *fp, off_t offset, int whence)
	{
	fpos_t (seekfn)(void , fpos_t, int);
	fpos_t target, curoff;
	size_t n;
	struct stat st;
	int havepos;

	/* make sure stdio is set up */
	if (!__sdidinit)
	__sinit();

	/*
	* Have to be able to seek.
	*/
	if ((seekfn = fp->_seek) == NULL) {
	errno = ESPIPE; /* historic practice */
	return (EOF);
	}

	/*
	* Change any SEEK_CUR to SEEK_SET, and check `whence' argument.
	* After this, whence is either SEEK_SET or SEEK_END.
	*/
	FLOCKFILE(fp);
	switch (whence) {

	case SEEK_CUR:
	/*
	* In order to seek relative to the current stream offset,
	* we have to first find the current stream offset a la
	* ftell (see ftell for details).
	*/
	__sflush(fp); /* may adjust seek offset on append stream */
	if (fp->_flags & __SOFF)
	curoff = fp->_offset;
	else {
	curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
	if (curoff == (fpos_t)-1) {
	FUNLOCKFILE(fp);
	return (EOF);
	}
	}
	if (fp->_flags & __SRD) {
	curoff -= fp->_r;
	if (HASUB(fp))
	curoff -= fp->_ur;
	} else if (fp->_flags & __SWR && fp->_p != NULL)
	curoff += fp->_p - fp->_bf._base;

	offset += curoff;
	whence = SEEK_SET;
	havepos = 1;
	break;

	case SEEK_SET:
	case SEEK_END:
	curoff = 0; /* XXX just to keep gcc quiet */
	havepos = 0;
	break;

	default:
	FUNLOCKFILE(fp);
	errno = EINVAL;
	return (EOF);
	}

	/*
	* Can only optimise if:
	* reading (and not reading-and-writing);
	* not unbuffered; and
	* this is a `regular' Unix file (and hence seekfn==__sseek).
	* We must check __NBF first, because it is possible to have __NBF
	* and __SOPT both set.
	*/
	if (fp->_bf._base == NULL)
	__smakebuf(fp);
	if (fp->_flags & (__SWR \| __SRW \| __SNBF \| __SNPT))
	goto dumb;
	if ((fp->_flags & __SOPT) == 0) {
	if (seekfn != __sseek \|\|
	fp->_file < 0 \|\| fstat(fp->_file, &st) \|\|
	(st.st_mode & S_IFMT) != S_IFREG) {
	fp->_flags \|= __SNPT;
	goto dumb;
	}
	fp->_blksize = st.st_blksize;
	fp->_flags \|= __SOPT;
	}

	/*
	* We are reading; we can try to optimise.
	* Figure out where we are going and where we are now.
	*/
	if (whence == SEEK_SET)
	target = offset;
	else {
	if (fstat(fp->_file, &st))
	goto dumb;
	target = st.st_size + offset;
	}

	if (!havepos) {
	if (fp->_flags & __SOFF)
	curoff = fp->_offset;
	else {
	curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
	if (curoff == POS_ERR)
	goto dumb;
	}
	curoff -= fp->_r;
	if (HASUB(fp))
	curoff -= fp->_ur;
	}

	/*
	* Compute the number of bytes in the input buffer (pretending
	* that any ungetc() input has been discarded). Adjust current
	* offset backwards by this count so that it represents the
	* file offset for the first byte in the current input buffer.
	*/
	if (HASUB(fp)) {
	curoff += fp->_r; /* kill off ungetc */
	n = fp->_up - fp->_bf._base;
	curoff -= n;
	n += fp->_ur;
	} else {
	n = fp->_p - fp->_bf._base;
	curoff -= n;
	n += fp->_r;
	}

	/*
	* If the target offset is within the current buffer,
	* simply adjust the pointers, clear EOF, undo ungetc(),
	* and return. (If the buffer was modified, we have to
	* skip this; see fgetln.c.)
	*/
	if ((fp->_flags & __SMOD) == 0 &&
	target >= curoff && target < (fpos_t)(curoff + n)) {
	int o = target - curoff;

	fp->_p = fp->_bf._base + o;
	fp->_r = n - o;
	if (HASUB(fp))
	FREEUB(fp);
	fp->_flags &= ~__SEOF;
	FUNLOCKFILE(fp);
	return (0);
	}

	/*
	* The place we want to get to is not within the current buffer,
	* but we can still be kind to the kernel copyout mechanism.
	* By aligning the file offset to a block boundary, we can let
	* the kernel use the VM hardware to map pages instead of
	* copying bytes laboriously. Using a block boundary also
	* ensures that we only read one block, rather than two.
	*/
	curoff = target & ~(fp->_blksize - 1);
	if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR)
	goto dumb;
	fp->_r = 0;
	fp->_p = fp->_bf._base;
	if (HASUB(fp))
	FREEUB(fp);
	fp->_flags &= ~__SEOF;
	n = target - curoff;
	if (n) {
	if (__srefill(fp) \|\| (size_t)fp->_r < n)
	goto dumb;
	fp->_p += n;
	fp->_r -= n;
	}
	FUNLOCKFILE(fp);
	return (0);

	/*
	* We get here if we cannot optimise the seek ... just
	* do it. Allow the seek function to change fp->_bf._base.
	*/
	dumb:
	if (__sflush(fp) \|\|
	(*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) {
	FUNLOCKFILE(fp);
	return (EOF);
	}
	/* success: clear EOF indicator and discard ungetc() data */
	if (HASUB(fp))
	FREEUB(fp);
	fp->_p = fp->_bf._base;
	fp->_r = 0;
	/* fp->_w = 0; / / unnecessary (I think...) */
	fp->_flags &= ~__SEOF;
	FUNLOCKFILE(fp);
	return (0);
	}

	/*
	* fseek()'s offset is a long and sizeof(off_t) != sizeof(long) on all arches
	*/
	#if defined(__alpha__) && defined(__indr_reference)
	__indr_reference(fseeko, fseek);
	#else
	int
	fseek(FILE *fp, long offset, int whence)
	{
	off_t off = offset;

	return(fseeko(fp, off, whence));
	}
	#endif