xref: /titanic_51/usr/src/lib/libast/common/sfio/sfseek.c (revision 36e852a172cba914383d7341c988128b2c667fbd)
1 /***********************************************************************
2 *                                                                      *
3 *               This software is part of the ast package               *
4 *          Copyright (c) 1985-2009 AT&T Intellectual Property          *
5 *                      and is licensed under the                       *
6 *                  Common Public License, Version 1.0                  *
7 *                    by AT&T Intellectual Property                     *
8 *                                                                      *
9 *                A copy of the License is available at                 *
10 *            http://www.opensource.org/licenses/cpl1.0.txt             *
11 *         (with md5 checksum 059e8cd6165cb4c31e351f2b69388fd9)         *
12 *                                                                      *
13 *              Information and Software Systems Research               *
14 *                            AT&T Research                             *
15 *                           Florham Park NJ                            *
16 *                                                                      *
17 *                 Glenn Fowler <gsf@research.att.com>                  *
18 *                  David Korn <dgk@research.att.com>                   *
19 *                   Phong Vo <kpv@research.att.com>                    *
20 *                                                                      *
21 ***********************************************************************/
22 #include	"sfhdr.h"
23 
24 /*	Set the IO pointer to a specific location in the stream
25 **
26 **	Written by Kiem-Phong Vo.
27 */
28 
29 #if __STD_C
30 static void newpos(Sfio_t* f, Sfoff_t p)
31 #else
32 static void newpos(f, p)
33 Sfio_t*	f;
34 Sfoff_t p;
35 #endif
36 {
37 #ifdef MAP_TYPE
38 	if((f->bits&SF_MMAP) && f->data)
39 	{	SFMUNMAP(f, f->data, f->endb-f->data);
40 		f->data = NIL(uchar*);
41 	}
42 #endif
43 	f->next = f->endr = f->endw = f->data;
44 	f->endb = (f->mode&SF_WRITE) ? f->data+f->size : f->data;
45 	if((f->here = p) < 0)
46 	{	f->extent = -1;
47 		f->here = 0;
48 	}
49 }
50 
51 #if __STD_C
52 Sfoff_t sfseek(Sfio_t* f, Sfoff_t p, int type)
53 #else
54 Sfoff_t sfseek(f,p,type)
55 Sfio_t*	f;	/* seek to a new location in this stream */
56 Sfoff_t	p;	/* place to seek to */
57 int	type;	/* 0: from org, 1: from here, 2: from end */
58 #endif
59 {
60 	Sfoff_t	r, s;
61 	int	mode, local, hardseek, mustsync;
62 	SFMTXDECL(f);
63 
64 	SFMTXENTER(f, (Sfoff_t)(-1));
65 
66 	GETLOCAL(f,local);
67 
68 	hardseek = (type|f->flags)&(SF_SHARE|SF_PUBLIC);
69 
70 	if(hardseek && f->mode == (SF_READ|SF_SYNCED) )
71 	{	newpos(f,f->here);
72 		f->mode = SF_READ;
73 	}
74 
75 	/* set and initialize the stream to a definite mode */
76 	if((int)SFMODE(f,local) != (mode = f->mode&SF_RDWR))
77 	{	int	flags = f->flags;
78 
79 		if(hardseek&SF_PUBLIC) /* seek ptr must follow file descriptor */
80 			f->flags |= SF_SHARE|SF_PUBLIC;
81 		mode = _sfmode(f,mode,local);
82 		if(hardseek&SF_PUBLIC)
83 			f->flags = flags;
84 
85 		if(mode < 0)
86 			SFMTXRETURN(f, (Sfoff_t)(-1));
87 	}
88 
89 	mustsync = (type&SF_SHARE) && !(type&SF_PUBLIC) &&
90 		   (f->mode&SF_READ) && !(f->flags&SF_STRING);
91 
92 	/* Xopen-compliant */
93 	if((type &= (SEEK_SET|SEEK_CUR|SEEK_END)) != SEEK_SET &&
94 	   type != SEEK_CUR && type != SEEK_END )
95 	{	errno = EINVAL;
96 		SFMTXRETURN(f, (Sfoff_t)(-1));
97 	}
98 
99 	if(f->extent < 0)
100 	{	/* let system call set errno */
101 		(void)SFSK(f,(Sfoff_t)0,SEEK_CUR,f->disc);
102 		SFMTXRETURN(f, (Sfoff_t)(-1));
103 	}
104 
105 	/* throw away ungetc data */
106 	if(f->disc == _Sfudisc)
107 		(void)sfclose((*_Sfstack)(f,NIL(Sfio_t*)));
108 
109 	/* lock the stream for internal manipulations */
110 	SFLOCK(f,local);
111 
112 	/* clear error and eof bits */
113 	f->flags &= ~(SF_EOF|SF_ERROR);
114 
115 	while(f->flags&SF_STRING)
116 	{	SFSTRSIZE(f);
117 
118 		if(type == SEEK_CUR)
119 			r = p + (f->next - f->data);
120 		else if(type == SEEK_END)
121 			r = p + f->extent;
122 		else	r = p;
123 
124 		if(r >= 0 && r <= f->size)
125 		{	p = r;
126 			f->next = f->data+p;
127 			f->here = p;
128 			if(p > f->extent)
129 				memclear((char*)(f->data+f->extent),(int)(p-f->extent));
130 			goto done;
131 		}
132 
133 		/* check exception handler, note that this may pop stream */
134 		if(SFSK(f,r,SEEK_SET,f->disc) != r)
135 		{	p = -1;
136 			goto done;
137 		}
138 		else if(!(f->flags&SF_STRING))
139 		{	p = r;
140 			goto done;
141 		}
142 	}
143 
144 	if(f->mode&SF_WRITE)
145 	{	/* see if we can avoid flushing buffer */
146 		if(!hardseek && type < SEEK_END && !(f->flags&SF_APPENDWR) )
147 		{	s = f->here + (f->next - f->data);
148 			r = p + (type == SEEK_SET ? 0 : s);
149 			if(r == s)
150 			{	p = r;
151 				goto done;
152 			}
153 		}
154 
155 		if(f->next > f->data && SFSYNC(f) < 0)
156 		{	p = -1;
157 			goto done;
158 		}
159 	}
160 
161 	if(type == SEEK_END || (f->mode&SF_WRITE) )
162 	{	if((hardseek&SF_PUBLIC) || type == SEEK_END)
163 			p = SFSK(f, p, type, f->disc);
164 		else
165 		{	r = p + (type == SEEK_CUR ? f->here : 0);
166 			p = (hardseek || r != f->here) ? SFSK(f,r,SEEK_SET,f->disc) : r;
167 		}
168 		if(p >= 0)
169 			newpos(f,p);
170 
171 		goto done;
172 	}
173 
174 	/* if get here, must be a read stream */
175 	s = f->here - (f->endb - f->next);
176 	r = p + (type == SEEK_CUR ? s : 0);
177 	if(r <= f->here && r >= (f->here - (f->endb-f->data)) )
178 	{	if((hardseek || (type == SEEK_CUR && p == 0)) )
179 		{	if((s = SFSK(f, (Sfoff_t)0, SEEK_CUR, f->disc)) == f->here ||
180 			   (s >= 0 && !(hardseek&SF_PUBLIC) &&
181 			    (s = SFSK(f, f->here, SEEK_SET, f->disc)) == f->here) )
182 				goto near_done;
183 			else if(s < 0)
184 			{	p = -1;
185 				goto done;
186 			}
187 			else
188 			{	newpos(f,s);
189 				hardseek = 0;
190 			}
191 		}
192 		else
193 		{ near_done:
194 			f->next = f->endb - (f->here - r);
195 			p = r;
196 			goto done;
197 		}
198 	}
199 
200 	/* desired position */
201 	if((p += type == SEEK_CUR ? s : 0) < 0)
202 		goto done;
203 
204 #ifdef MAP_TYPE
205 	if(f->bits&SF_MMAP)
206 	{	/* if mmap is not great, stop mmaping if moving around too much */
207 #if _mmap_worthy < 2
208 		if((f->next - f->data) < ((f->endb - f->data)/4) )
209 		{	SFSETBUF(f,(Void_t*)f->tiny,(size_t)SF_UNBOUND);
210 			hardseek = 1; /* this forces a hard seek below */
211 		}
212 		else
213 #endif
214 		{	/* for mmap, f->here can be virtual except for hardseek */
215 			newpos(f,p);
216 			if(!hardseek)
217 				goto done;
218 		}
219 	}
220 #endif
221 
222 	if(f->endb > f->next)
223 	{	/* reduce wastage in future buffer fillings */
224 		f->iosz = (f->next - f->data) + (f->endb - f->next)/2;
225 		f->iosz = ((f->iosz + f->blksz-1)/f->blksz)*f->blksz;
226 	}
227 	if(f->iosz >= f->size)
228 		f->iosz = 0;
229 
230 	/* buffer is now considered empty */
231 	f->next = f->endr = f->endb = f->data;
232 
233 	/* small backseeks often come in bunches, so seek back as far as possible */
234 	if(p < f->lpos && f->size > f->blksz && (p + f->blksz) > s)
235 	{	if((r = s - f->size) < 0)
236 			r = 0;
237 	}
238 	/* try to align buffer to block boundary to enhance I/O speed */
239 	else if(f->blksz > 0 && f->size >= 2*f->blksz)
240 		r = p - (p%f->blksz);
241 	else
242 	{	r = p;
243 
244 		/* seeking around and wasting data, be conservative */
245 		if(f->iosz > 0 && (p > f->lpos || p < f->lpos-f->size) )
246 			f->bits |= SF_JUSTSEEK;
247 	}
248 
249 	if((hardseek || r != f->here) && (f->here = SFSK(f,r,SEEK_SET,f->disc)) != r)
250 	{	if(r < p) /* now try to just get to p */
251 			f->here = SFSK(f,p,SEEK_SET,f->disc);
252 		if(f->here != p)
253 			p = -1;
254 		goto done;
255 	}
256 
257 	if(r < p) /* read to cover p */
258 	{	(void)SFRD(f, f->data, f->size, f->disc);
259 		if(p <= f->here && p >= (f->here - (f->endb - f->data)) )
260 			f->next = f->endb - (size_t)(f->here-p);
261 		else /* recover from read failure by just seeking to p */
262 		{	f->next = f->endb = f->data;
263 			if((f->here = SFSK(f,p,SEEK_SET,f->disc)) != p)
264 				p = -1;
265 		}
266 	}
267 
268 done :
269 	if(f->here < 0) /* hasn't been the best of time */
270 	{	f->extent = -1;
271 		f->here = 0;
272 	}
273 
274 	f->lpos = p;
275 
276 	SFOPEN(f,local);
277 
278 	if(mustsync)
279 		sfsync(f);
280 	SFMTXRETURN(f, p);
281 }
282