sfseek.c revision da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968
/***********************************************************************
* *
* This software is part of the ast package *
* Copyright (c) 1985-2007 AT&T Knowledge Ventures *
* and is licensed under the *
* Common Public License, Version 1.0 *
* by AT&T Knowledge Ventures *
* *
* A copy of the License is available at *
* http://www.opensource.org/licenses/cpl1.0.txt *
* (with md5 checksum 059e8cd6165cb4c31e351f2b69388fd9) *
* *
* Information and Software Systems Research *
* AT&T Research *
* Florham Park NJ *
* *
* Glenn Fowler <gsf@research.att.com> *
* David Korn <dgk@research.att.com> *
* Phong Vo <kpv@research.att.com> *
* *
***********************************************************************/
#include "sfhdr.h"
/* Set the IO pointer to a specific location in the stream
**
** Written by Kiem-Phong Vo.
*/
#if __STD_C
static void newpos(Sfio_t* f, Sfoff_t p)
#else
static void newpos(f, p)
Sfio_t* f;
Sfoff_t p;
#endif
{
#ifdef MAP_TYPE
if((f->bits&SF_MMAP) && f->data)
{ SFMUNMAP(f, f->data, f->endb-f->data);
f->data = NIL(uchar*);
}
#endif
f->next = f->endr = f->endw = f->data;
f->endb = (f->mode&SF_WRITE) ? f->data+f->size : f->data;
if((f->here = p) < 0)
{ f->extent = -1;
f->here = 0;
}
}
#if __STD_C
Sfoff_t sfseek(Sfio_t* f, Sfoff_t p, int type)
#else
Sfoff_t sfseek(f,p,type)
Sfio_t* f; /* seek to a new location in this stream */
Sfoff_t p; /* place to seek to */
int type; /* 0: from org, 1: from here, 2: from end */
#endif
{
Sfoff_t r, s;
int mode, local, hardseek, mustsync;
SFMTXSTART(f, (Sfoff_t)(-1));
GETLOCAL(f,local);
hardseek = (type|f->flags)&(SF_SHARE|SF_PUBLIC);
if(hardseek && f->mode == (SF_READ|SF_SYNCED) )
{ newpos(f,f->here);
f->mode = SF_READ;
}
/* set and initialize the stream to a definite mode */
if((int)SFMODE(f,local) != (mode = f->mode&SF_RDWR))
{ int flags = f->flags;
if(hardseek&SF_PUBLIC) /* seek ptr must follow file descriptor */
f->flags |= SF_SHARE|SF_PUBLIC;
mode = _sfmode(f,mode,local);
if(hardseek&SF_PUBLIC)
f->flags = flags;
if(mode < 0)
SFMTXRETURN(f, (Sfoff_t)(-1));
}
mustsync = (type&SF_SHARE) && !(type&SF_PUBLIC) &&
(f->mode&SF_READ) && !(f->flags&SF_STRING);
/* Xopen-compliant */
if((type &= (SEEK_SET|SEEK_CUR|SEEK_END)) != SEEK_SET &&
type != SEEK_CUR && type != SEEK_END )
{ errno = EINVAL;
SFMTXRETURN(f, (Sfoff_t)(-1));
}
if(f->extent < 0)
{ /* let system call set errno */
(void)SFSK(f,(Sfoff_t)0,SEEK_CUR,f->disc);
SFMTXRETURN(f, (Sfoff_t)(-1));
}
/* throw away ungetc data */
if(f->disc == _Sfudisc)
(void)sfclose((*_Sfstack)(f,NIL(Sfio_t*)));
/* lock the stream for internal manipulations */
SFLOCK(f,local);
/* clear error and eof bits */
f->flags &= ~(SF_EOF|SF_ERROR);
while(f->flags&SF_STRING)
{ SFSTRSIZE(f);
if(type == SEEK_CUR)
r = p + (f->next - f->data);
else if(type == SEEK_END)
r = p + f->extent;
else r = p;
if(r >= 0 && r <= f->size)
{ p = r;
f->next = f->data+p;
f->here = p;
if(p > f->extent)
memclear((char*)(f->data+f->extent),(int)(p-f->extent));
goto done;
}
/* check exception handler, note that this may pop stream */
if(SFSK(f,r,SEEK_SET,f->disc) != r)
{ p = -1;
goto done;
}
else if(!(f->flags&SF_STRING))
{ p = r;
goto done;
}
}
if(f->mode&SF_WRITE)
{ /* see if we can avoid flushing buffer */
if(!hardseek && type < SEEK_END && !(f->flags&SF_APPENDWR) )
{ s = f->here + (f->next - f->data);
r = p + (type == SEEK_SET ? 0 : s);
if(r == s)
{ p = r;
goto done;
}
}
if(f->next > f->data && SFSYNC(f) < 0)
{ p = -1;
goto done;
}
}
if(type == SEEK_END || (f->mode&SF_WRITE) )
{ if((hardseek&SF_PUBLIC) || type == SEEK_END)
p = SFSK(f, p, type, f->disc);
else
{ r = p + (type == SEEK_CUR ? f->here : 0);
p = (hardseek || r != f->here) ? SFSK(f,r,SEEK_SET,f->disc) : r;
}
if(p >= 0)
newpos(f,p);
goto done;
}
/* if get here, must be a read stream */
s = f->here - (f->endb - f->next);
r = p + (type == SEEK_CUR ? s : 0);
if(r <= f->here && r >= (f->here - (f->endb-f->data)) )
{ if((hardseek || (type == SEEK_CUR && p == 0)) )
{ if((s = SFSK(f, (Sfoff_t)0, SEEK_CUR, f->disc)) == f->here ||
(s >= 0 && !(hardseek&SF_PUBLIC) &&
(s = SFSK(f, f->here, SEEK_SET, f->disc)) == f->here) )
goto near_done;
else if(s < 0)
{ p = -1;
goto done;
}
else
{ newpos(f,s);
hardseek = 0;
}
}
else
{ near_done:
f->next = f->endb - (f->here - r);
p = r;
goto done;
}
}
/* desired position */
if((p += type == SEEK_CUR ? s : 0) < 0)
goto done;
#ifdef MAP_TYPE
if(f->bits&SF_MMAP)
{ /* if mmap is not great, stop mmaping if moving around too much */
#if _mmap_worthy < 2
if((f->next - f->data) < ((f->endb - f->data)/4) )
{ SFSETBUF(f,(Void_t*)f->tiny,(size_t)SF_UNBOUND);
hardseek = 1; /* this forces a hard seek below */
}
else
#endif
{ /* for mmap, f->here can be virtual except for hardseek */
newpos(f,p);
if(!hardseek)
goto done;
}
}
#endif
if(f->endb > f->next)
{ /* reduce wastage in future buffer fillings */
f->iosz = (f->next - f->data) + (f->endb - f->next)/2;
f->iosz = ((f->iosz + f->blksz-1)/f->blksz)*f->blksz;
}
if(f->iosz >= f->size)
f->iosz = 0;
/* buffer is now considered empty */
f->next = f->endr = f->endb = f->data;
/* small backseeks often come in bunches, so seek back as far as possible */
if(p < f->lpos && f->size > f->blksz && (p + f->blksz) > s)
{ if((r = s - f->size) < 0)
r = 0;
}
/* try to align buffer to block boundary to enhance I/O speed */
else if(f->blksz > 0 && f->size >= 2*f->blksz)
r = p - (p%f->blksz);
else
{ r = p;
/* seeking around and wasting data, be conservative */
if(f->iosz > 0 && (p > f->lpos || p < f->lpos-f->size) )
f->bits |= SF_JUSTSEEK;
}
if((hardseek || r != f->here) && (f->here = SFSK(f,r,SEEK_SET,f->disc)) != r)
{ if(r < p) /* now try to just get to p */
f->here = SFSK(f,p,SEEK_SET,f->disc);
if(f->here != p)
p = -1;
goto done;
}
if(r < p) /* read to cover p */
{ (void)SFRD(f, f->data, f->size, f->disc);
if(p <= f->here && p >= (f->here - (f->endb - f->data)) )
f->next = f->endb - (size_t)(f->here-p);
else /* recover from read failure by just seeking to p */
{ f->next = f->endb = f->data;
if((f->here = SFSK(f,p,SEEK_SET,f->disc)) != p)
p = -1;
}
}
done :
if(f->here < 0) /* hasn't been the best of time */
{ f->extent = -1;
f->here = 0;
}
f->lpos = p;
SFOPEN(f,local);
if(mustsync)
sfsync(f);
SFMTXRETURN(f, p);
}