[unix-history] / usr / src / lib / libc / stdio / fseek.c

/*-
 * Copyright (c) 1990 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. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. 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.
 */

#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)fseek.c	5.7 (Berkeley) 2/24/91";
#endif /* LIBC_SCCS and not lint */

#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.
 */
fseek(fp, offset, whence)
	register FILE *fp;
	long offset;
	int whence;
{
#if __STDC__
	register fpos_t (*seekfn)(void *, fpos_t, int);
#else
	register fpos_t (*seekfn)();
#endif
	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.
	 */
	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).
		 */
		if (fp->_flags & __SOFF)
			curoff = fp->_offset;
		else {
			curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
			if (curoff == -1L)
				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:
		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, 0L, 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)) {
		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 fgetline.c.)
	 */
	if ((fp->_flags & __SMOD) == 0 &&
	    target >= curoff && target < curoff + n) {
		register int o = target - curoff;

		fp->_p = fp->_bf._base + o;
		fp->_r = n - o;
		if (HASUB(fp))
			FREEUB(fp);
		fp->_flags &= ~__SEOF;
		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;
	if (HASUB(fp))
		FREEUB(fp);
	fp->_flags &= ~__SEOF;
	n = target - curoff;
	if (n) {
		if (__srefill(fp) || fp->_r < n)
			goto dumb;
		fp->_p += n;
		fp->_r -= n;
	}
	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, offset, whence) == POS_ERR) {
		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;
	return (0);
}
Commit	Line	Data
8d2f28ac WJ	1	/*-
	2	* Copyright (c) 1990 The Regents of the University of California.
	3	* All rights reserved.
	4	*
	5	* This code is derived from software contributed to Berkeley by
	6	* Chris Torek.
	7	*
	8	* Redistribution and use in source and binary forms, with or without
	9	* modification, are permitted provided that the following conditions
	10	* are met:
	11	* 1. Redistributions of source code must retain the above copyright
	12	* notice, this list of conditions and the following disclaimer.
	13	* 2. Redistributions in binary form must reproduce the above copyright
	14	* notice, this list of conditions and the following disclaimer in the
	15	* documentation and/or other materials provided with the distribution.
	16	* 3. All advertising materials mentioning features or use of this software
	17	* must display the following acknowledgement:
	18	* This product includes software developed by the University of
	19	* California, Berkeley and its contributors.
	20	* 4. Neither the name of the University nor the names of its contributors
	21	* may be used to endorse or promote products derived from this software
	22	* without specific prior written permission.
	23	*
	24	* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	25	* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	26	* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	27	* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	28	* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	29	* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	30	* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	31	* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	32	* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	33	* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	34	* SUCH DAMAGE.
	35	*/
	36
	37	#if defined(LIBC_SCCS) && !defined(lint)
	38	static char sccsid[] = "@(#)fseek.c 5.7 (Berkeley) 2/24/91";
	39	#endif /* LIBC_SCCS and not lint */
	40
	41	#include <sys/types.h>
	42	#include <sys/stat.h>
	43	#include <fcntl.h>
	44	#include <stdio.h>
	45	#include <stdlib.h>
	46	#include <errno.h>
	47	#include "local.h"
	48
	49	#define POS_ERR (-(fpos_t)1)
	50
	51	/*
	52	* Seek the given file to the given offset.
	53	* `Whence' must be one of the three SEEK_* macros.
	54	*/
	55	fseek(fp, offset, whence)
	56	register FILE *fp;
	57	long offset;
	58	int whence;
	59	{
	60	#if __STDC__
	61	register fpos_t (seekfn)(void , fpos_t, int);
	62	#else
	63	register fpos_t (*seekfn)();
	64	#endif
65	fpos_t target, curoff;
66	size_t n;
67	struct stat st;
68	int havepos;
69
70	/* make sure stdio is set up */
71	if (!__sdidinit)
72	__sinit();
73
74	/*
75	* Have to be able to seek.
76	*/
77	if ((seekfn = fp->_seek) == NULL) {
78	errno = ESPIPE; /* historic practice */
79	return (EOF);
80	}
81
82	/*
83	* Change any SEEK_CUR to SEEK_SET, and check `whence' argument.
84	* After this, whence is either SEEK_SET or SEEK_END.
85	*/
86	switch (whence) {
87
88	case SEEK_CUR:
89	/*
90	* In order to seek relative to the current stream offset,
91	* we have to first find the current stream offset a la
92	* ftell (see ftell for details).
93	*/
94	if (fp->_flags & __SOFF)
95	curoff = fp->_offset;
96	else {
97	curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
98	if (curoff == -1L)
99	return (EOF);
100	}
101	if (fp->_flags & __SRD) {
102	curoff -= fp->_r;
103	if (HASUB(fp))
104	curoff -= fp->_ur;
105	} else if (fp->_flags & __SWR && fp->_p != NULL)
106	curoff += fp->_p - fp->_bf._base;
107
108	offset += curoff;
109	whence = SEEK_SET;
110	havepos = 1;
111	break;
112
113	case SEEK_SET:
114	case SEEK_END:
115	curoff = 0; /* XXX just to keep gcc quiet */
116	havepos = 0;
117	break;
118
119	default:
120	errno = EINVAL;
121	return (EOF);
122	}
123
124	/*
125	* Can only optimise if:
126	* reading (and not reading-and-writing);
127	* not unbuffered; and
128	* this is a `regular' Unix file (and hence seekfn==__sseek).
129	* We must check __NBF first, because it is possible to have __NBF
130	* and __SOPT both set.
131	*/
132	if (fp->_bf._base == NULL)
133	__smakebuf(fp);
134	if (fp->_flags & (__SWR \| __SRW \| __SNBF \| __SNPT))
135	goto dumb;
136	if ((fp->_flags & __SOPT) == 0) {
137	if (seekfn != __sseek \|\|
138	fp->_file < 0 \|\| fstat(fp->_file, &st) \|\|
139	(st.st_mode & S_IFMT) != S_IFREG) {
140	fp->_flags \|= __SNPT;
141	goto dumb;
142	}
143	fp->_blksize = st.st_blksize;
144	fp->_flags \|= __SOPT;
145	}
146
147	/*
148	* We are reading; we can try to optimise.
149	* Figure out where we are going and where we are now.
150	*/
151	if (whence == SEEK_SET)
152	target = offset;
153	else {
154	if (fstat(fp->_file, &st))
155	goto dumb;
156	target = st.st_size + offset;
157	}
158
159	if (!havepos) {
160	if (fp->_flags & __SOFF)
161	curoff = fp->_offset;
162	else {
163	curoff = (*seekfn)(fp->_cookie, 0L, SEEK_CUR);
164	if (curoff == POS_ERR)
165	goto dumb;
166	}
167	curoff -= fp->_r;
168	if (HASUB(fp))
169	curoff -= fp->_ur;
170	}
171
172	/*
173	* Compute the number of bytes in the input buffer (pretending
174	* that any ungetc() input has been discarded). Adjust current
175	* offset backwards by this count so that it represents the
176	* file offset for the first byte in the current input buffer.
177	*/
178	if (HASUB(fp)) {
179	n = fp->_up - fp->_bf._base;
180	curoff -= n;
181	n += fp->_ur;
182	} else {
183	n = fp->_p - fp->_bf._base;
184	curoff -= n;
185	n += fp->_r;
186	}
187
188	/*
189	* If the target offset is within the current buffer,
190	* simply adjust the pointers, clear EOF, undo ungetc(),
191	* and return. (If the buffer was modified, we have to
192	* skip this; see fgetline.c.)
193	*/
194	if ((fp->_flags & __SMOD) == 0 &&
195	target >= curoff && target < curoff + n) {
196	register int o = target - curoff;
197
198	fp->_p = fp->_bf._base + o;
199	fp->_r = n - o;
200	if (HASUB(fp))
201	FREEUB(fp);
202	fp->_flags &= ~__SEOF;
203	return (0);
204	}
205
206	/*
207	* The place we want to get to is not within the current buffer,
208	* but we can still be kind to the kernel copyout mechanism.
209	* By aligning the file offset to a block boundary, we can let
210	* the kernel use the VM hardware to map pages instead of
211	* copying bytes laboriously. Using a block boundary also
212	* ensures that we only read one block, rather than two.
213	*/
214	curoff = target & ~(fp->_blksize - 1);
215	if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR)
216	goto dumb;
217	fp->_r = 0;
218	if (HASUB(fp))
219	FREEUB(fp);
220	fp->_flags &= ~__SEOF;
221	n = target - curoff;
222	if (n) {
223	if (__srefill(fp) \|\| fp->_r < n)
224	goto dumb;
225	fp->_p += n;
226	fp->_r -= n;
227	}
228	return (0);
229
230	/*
231	* We get here if we cannot optimise the seek ... just
232	* do it. Allow the seek function to change fp->_bf._base.
233	*/
234	dumb:
235	if (__sflush(fp) \|\|
236	(*seekfn)(fp->_cookie, offset, whence) == POS_ERR) {
237	return (EOF);
238	}
239	/* success: clear EOF indicator and discard ungetc() data */
240	if (HASUB(fp))
241	FREEUB(fp);
242	fp->_p = fp->_bf._base;
243	fp->_r = 0;
244	/* fp->_w = 0; / / unnecessary (I think...) */
245	fp->_flags &= ~__SEOF;
246	return (0);
247	}