/*
 *	Copyright 1996, University Corporation for Atmospheric Research
 *	See netcdf/COPYRIGHT file for copying and redistribution conditions.
 */
/* $Id: posixio.c,v 1.68 1999/08/24 17:18:19 steve Exp $ */

#include "ncconfig.h"
#include <assert.h>
#include <stdlib.h>
#include <errno.h>
#ifndef ENOERR
#define ENOERR 0
#endif
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#ifdef _MSC_VER /* Microsoft Compilers */
#include <io.h>
#else
#include <unistd.h>
#endif

#ifndef SEEK_SET
#define SEEK_SET 0
#define SEEK_CUR 1
#define SEEK_END 2
#endif

#include "ncio.h"
#include "fbits.h"
#include "rnd.h"

/* #define INSTRUMENT 1 */
#if INSTRUMENT /* debugging */
#undef NDEBUG
#include <stdio.h>
#include "instr.h"
#endif

#undef MIN  /* system may define MIN somewhere and complain */
#define MIN(mm,nn) (((mm) < (nn)) ? (mm) : (nn))

#if !defined(NDEBUG) && !defined(X_INT_MAX)
#define  X_INT_MAX 2147483647
#endif

#if 0 /* !defined(NDEBUG) && !defined(X_ALIGN) */
#define  X_ALIGN 4
#else
#undef X_ALIGN
#endif

/*
 * Define the following for debugging.
 */
/* #define ALWAYS_NC_SHARE 1 */

/* Begin OS */

static int ncio_px_sync(ncio *const nciop);

#ifndef POSIXIO_DEFAULT_PAGESIZE
#define POSIXIO_DEFAULT_PAGESIZE 4096
#endif
/*
 * What is the system pagesize?
 */
static size_t
pagesize(void)
{
/* Hmm, aren't standards great? */
#if defined(_SC_PAGE_SIZE) && !defined(_SC_PAGESIZE)
#define _SC_PAGESIZE _SC_PAGE_SIZE
#endif

#ifdef _SC_PAGESIZE
	{
		const long pgsz = sysconf(_SC_PAGESIZE);
		if(pgsz > 0)
			return (size_t) pgsz;
		/* else, silent in the face of error */
	}
#elif defined(HAVE_GETPAGESIZE)
	return (size_t) getpagesize();
#endif
	return (size_t) POSIXIO_DEFAULT_PAGESIZE;
}

/*
 * What is the preferred I/O block size?
 */
static size_t
blksize(int fd)
{
#if defined(HAVE_ST_BLKSIZE)
	struct stat sb;
	if (fstat(fd, &sb) > -1)
	{
		if(sb.st_blksize >= 8192)
			return (size_t) sb.st_blksize;
		return 8192;
	}
	/* else, silent in the face of error */
#endif
	return (size_t) 2 * pagesize();
}


/*
 * Sortof like ftruncate, except won't make the
 * file shorter.
 */
static int
fgrow(const int fd, const off_t len)
{
	struct stat sb;
	if (fstat(fd, &sb) < 0)
		return errno;
	if (len < sb.st_size)
		return ENOERR;
#if defined(HAVE_FTRUNCATE)
	if (ftruncate(fd, len) < 0)
		return errno;
#else
	{
		const long dumb = 0;
			/* cache current position */
		const off_t pos = lseek(fd, 0, SEEK_CUR);
		if(pos < 0)
			return errno;
		if (lseek(fd, len-sizeof(dumb), SEEK_SET) < 0)
			return errno;
		if(write(fd, &dumb, sizeof(dumb)) < 0)
			return errno;
		if (lseek(fd, pos, SEEK_SET) < 0)
			return errno;
	}
#endif /* HAVE_FTRUNCATE */
	/* else */
	return ENOERR;
}

/* End OS */
/* Begin px */

static int
px_pgout(ncio *const nciop, 
	off_t const offset,  const size_t extent,
	void *const vp, off_t *posp)
{
#ifdef X_ALIGN
	assert(offset % X_ALIGN == 0);
#endif

	assert(*posp == OFF_NONE || *posp == lseek(nciop->fd, 0, SEEK_CUR));

	if(*posp != offset)
	{
		if(lseek(nciop->fd, offset, SEEK_SET) != offset)
		{
			return errno;
		}
		*posp = offset;
	}
	if(write(nciop->fd, vp, extent) != (ssize_t) extent)
	{
		return errno;
	}
	*posp += extent;

	return ENOERR;
}


static int
px_pgin(ncio *const nciop,
	off_t const offset, const size_t extent,
	void *const vp, size_t *nreadp, off_t *posp)
{
	int status;
	ssize_t nread;

#ifdef X_ALIGN
	assert(offset % X_ALIGN == 0);
	assert(extent % X_ALIGN == 0);
#endif

	assert(*posp == OFF_NONE || *posp == lseek(nciop->fd, 0, SEEK_CUR));

	if(*posp != offset)
	{
		if(lseek(nciop->fd, offset, SEEK_SET) != offset)
		{
			status = errno;
			return status;
		}
		*posp = offset;
	}

	errno = 0;
	nread = read(nciop->fd, vp, extent);
	if(nread != (ssize_t) extent)
	{
		status = errno;
		if(nread == -1 || status != ENOERR)
			return status;
		/* else it's okay we read less than asked for */
		(void) memset((char *)vp + nread, 0, (ssize_t)extent - nread);
	}
	*nreadp = nread;
	*posp += nread;

	return ENOERR;
}


typedef struct ncio_px {
	size_t blksz;
	off_t pos;
	/* buffer */
	off_t	bf_offset; 
	size_t	bf_extent;
	size_t	bf_cnt;
	void	*bf_base;
	int	bf_rflags;
	int	bf_refcount;
	/* chain for double buffering in px_move */
	struct ncio_px *slave;
} ncio_px;


/*ARGSUSED*/
static int
px_rel(ncio_px *const pxp, off_t offset, int rflags)
{
	assert(pxp->bf_offset <= offset
		 && offset < pxp->bf_offset + (off_t) pxp->bf_extent);
	assert(pIf(fIsSet(rflags, RGN_MODIFIED),
		fIsSet(pxp->bf_rflags, RGN_WRITE)));

	if(fIsSet(rflags, RGN_MODIFIED))
	{
		fSet(pxp->bf_rflags, RGN_MODIFIED);
	}
	pxp->bf_refcount--;

	return ENOERR;
}

static int
ncio_px_rel(ncio *const nciop, off_t offset, int rflags)
{
	ncio_px *const pxp = (ncio_px *)nciop->pvt;

	if(fIsSet(rflags, RGN_MODIFIED) && !fIsSet(nciop->ioflags, NC_WRITE))
		return EPERM; /* attempt to write readonly file */

	return px_rel(pxp, offset, rflags);
}

static int
px_get(ncio *const nciop, ncio_px *const pxp,
		off_t offset, size_t extent,
		int rflags,
		void **const vpp)
{
	int status = ENOERR;

	const off_t blkoffset = _RNDDOWN(offset, (off_t)pxp->blksz);
	size_t diff = (size_t)(offset - blkoffset);
	size_t blkextent = _RNDUP(diff + extent, pxp->blksz);
	
	assert(extent != 0);
	assert(extent < X_INT_MAX); /* sanity check */
	assert(offset >= 0); /* sanity check */
	assert(offset < X_INT_MAX); /* sanity check */

	if(2 * pxp->blksz < blkextent)
		return E2BIG; /* TODO: temporary kludge */
	if(pxp->bf_offset == OFF_NONE)
	{
		/* Uninitialized */
		if(pxp->bf_base == NULL)
		{
			assert(pxp->bf_extent == 0);
			assert(blkextent <= 2 * pxp->blksz);
			pxp->bf_base = malloc(2 * pxp->blksz);
			if(pxp->bf_base == NULL)
				return ENOMEM;
		}
		goto pgin;
	}
	/* else */
	assert(blkextent <= 2 * pxp->blksz);

	if(blkoffset == pxp->bf_offset)
	{
		/* hit */
 		if(blkextent > pxp->bf_extent) 
		{
			/* page in upper */
			void *const middle =
			 	(void *)((char *)pxp->bf_base + pxp->blksz);
			assert(pxp->bf_extent == pxp->blksz);
			status = px_pgin(nciop,
				 pxp->bf_offset + (off_t)pxp->blksz,
				 pxp->blksz,
				 middle,
				 &pxp->bf_cnt,
				 &pxp->pos);
			if(status != ENOERR)
				return status;
			pxp->bf_extent = 2 * pxp->blksz;
			pxp->bf_cnt += pxp->blksz;
		}
		goto done;
	}
	/* else */

	if(pxp->bf_extent > pxp->blksz
		 && blkoffset == pxp->bf_offset + pxp->blksz)
	{
		/* hit in upper half */
		if(blkextent == pxp->blksz)
		{
			/* all in upper half, no fault needed */
			diff += pxp->blksz;
			goto done;
		}
		/* else */
		if(pxp->bf_cnt > pxp->blksz)
		{
			/* data in upper half */
			void *const middle =
				(void *)((char *)pxp->bf_base + pxp->blksz);
			assert(pxp->bf_extent == 2 * pxp->blksz);
			if(fIsSet(pxp->bf_rflags, RGN_MODIFIED))
			{
				/* page out lower half */
				assert(pxp->bf_refcount <= 0);
				status = px_pgout(nciop,
					pxp->bf_offset,
					pxp->blksz,
					pxp->bf_base,
					&pxp->pos);
				if(status != ENOERR)
					return status;
			}
			pxp->bf_cnt -= pxp->blksz;
			/* copy upper half into lower half */
			(void) memcpy(pxp->bf_base, middle, pxp->bf_cnt);
		}
		pxp->bf_offset = blkoffset;
		/* pxp->bf_extent = pxp->blksz; */

 		assert(blkextent == 2 * pxp->blksz);
		{
			/* page in upper */
			void *const middle =
			 	(void *)((char *)pxp->bf_base + pxp->blksz);
			status = px_pgin(nciop,
				 pxp->bf_offset + (off_t)pxp->blksz,
				 pxp->blksz,
				 middle,
				 &pxp->bf_cnt,
				 &pxp->pos);
			if(status != ENOERR)
				return status;
			pxp->bf_extent = 2 * pxp->blksz;
			pxp->bf_cnt += pxp->blksz;
		}
		goto done;
	}
	/* else */

	if(blkoffset == pxp->bf_offset - pxp->blksz)
	{
		/* wants the page below */
		void *const middle =
			(void *)((char *)pxp->bf_base + pxp->blksz);
		size_t upper_cnt = 0;
		if(pxp->bf_cnt > pxp->blksz)
		{
			/* data in upper half */
			assert(pxp->bf_extent == 2 * pxp->blksz);
			if(fIsSet(pxp->bf_rflags, RGN_MODIFIED))
			{
				/* page out upper half */
				assert(pxp->bf_refcount <= 0);
				status = px_pgout(nciop,
					pxp->bf_offset + (off_t)pxp->blksz,
					pxp->bf_cnt - pxp->blksz,
					middle,
					&pxp->pos);
				if(status != ENOERR)
					return status;
			}
			pxp->bf_cnt = pxp->blksz;
			pxp->bf_extent = pxp->blksz;
		}
		if(pxp->bf_cnt > 0)
		{
			/* copy lower half into upper half */
			(void) memcpy(middle, pxp->bf_base, pxp->blksz);
			upper_cnt = pxp->bf_cnt;
		}
		/* read page below into lower half */
		status = px_pgin(nciop,
			 blkoffset,
			 pxp->blksz,
			 pxp->bf_base,
			 &pxp->bf_cnt,
			 &pxp->pos);
		if(status != ENOERR)
			return status;
		pxp->bf_offset = blkoffset;
		if(upper_cnt != 0)
		{
			pxp->bf_extent = 2 * pxp->blksz;
			pxp->bf_cnt = pxp->blksz + upper_cnt;
		}
		else
		{
			pxp->bf_extent = pxp->blksz;
		}
		goto done;
	}
	/* else */

	/* no overlap */
	if(fIsSet(pxp->bf_rflags, RGN_MODIFIED))
	{
		assert(pxp->bf_refcount <= 0);
		status = px_pgout(nciop,
			pxp->bf_offset,
			pxp->bf_cnt,
			pxp->bf_base,
			&pxp->pos);
		if(status != ENOERR)
			return status;
		pxp->bf_rflags = 0;
	}

pgin:
	status = px_pgin(nciop,
		 blkoffset,
		 blkextent,
		 pxp->bf_base,
		 &pxp->bf_cnt,
		 &pxp->pos);
	if(status != ENOERR)
		return status;
	 pxp->bf_offset = blkoffset;
	 pxp->bf_extent = blkextent;

done:
	extent += diff;
	if(pxp->bf_cnt < extent)
		pxp->bf_cnt = extent;
	assert(pxp->bf_cnt <= pxp->bf_extent);

	pxp->bf_rflags |= rflags;
	pxp->bf_refcount++;

	*vpp = (char *)pxp->bf_base + diff;
	return ENOERR;
}

static int
ncio_px_get(ncio *const nciop, 
		off_t offset, size_t extent,
		int rflags,
		void **const vpp)	/* NULL => force read */
{
	ncio_px *const pxp = (ncio_px *)nciop->pvt;
	
	if(fIsSet(rflags, RGN_WRITE) && !fIsSet(nciop->ioflags, NC_WRITE))
		return EPERM; /* attempt to write readonly file */

	/*
         * If the base of the stream buffer is NULL, then a read is forced
         * for synchronization purposes (see fault_v1hs() in v1hpg.c).  The
         * implementation is based on ncio_spx_rel() in this file.
	 */
	if (*vpp == NULL)
	{
	    ncio_px_sync(nciop);
	    pxp->bf_offset = OFF_NONE;
	    pxp->bf_cnt = 0;
	}

	/* reclaim space used in move */
	if(pxp->slave != NULL)
	{
		if(pxp->slave->bf_base != NULL)
		{
			free(pxp->slave->bf_base);
			pxp->slave->bf_base = NULL;
			pxp->slave->bf_extent = 0;
			pxp->slave->bf_offset = OFF_NONE;
		}
		free(pxp->slave);
		pxp->slave = NULL;
	}
	return px_get(nciop, pxp, offset, extent, rflags, vpp);
}


/* ARGSUSED */
static int
px_double_buffer(ncio *const nciop, off_t to, off_t from,
			size_t nbytes, int rflags)
{
	ncio_px *const pxp = (ncio_px *)nciop->pvt;
	int status = ENOERR;
	void *src;
	void *dest;
	
#if INSTRUMENT
fprintf(stderr, "\tdouble_buffr %ld %ld %ld\n",
		 (long)to, (long)from, (long)nbytes);
#endif
	status = px_get(nciop, pxp, to, nbytes, RGN_WRITE,
			&dest);
	if(status != ENOERR)
		return status;

	if(pxp->slave == NULL)
	{
		pxp->slave = (ncio_px *) malloc(sizeof(ncio_px));
		if(pxp->slave == NULL)
			return ENOMEM;

		pxp->slave->blksz = pxp->blksz;
		/* pos done below */
		pxp->slave->bf_offset = pxp->bf_offset; 
		pxp->slave->bf_extent = pxp->bf_extent;
		pxp->slave->bf_cnt = pxp->bf_cnt;
		pxp->slave->bf_base = malloc(2 * pxp->blksz);
		if(pxp->slave->bf_base == NULL)
			return ENOMEM;
		(void) memcpy(pxp->slave->bf_base, pxp->bf_base,
			 pxp->bf_extent);
		pxp->slave->bf_rflags = 0;
		pxp->slave->bf_refcount = 0;
		pxp->slave->slave = NULL;
	}
	
	pxp->slave->pos = pxp->pos;
	status = px_get(nciop, pxp->slave, from, nbytes, 0,
			&src);
	if(status != ENOERR)
		return status;
	if(pxp->pos != pxp->slave->pos)
	{
		/* position changed, sync */
		pxp->pos = pxp->slave->pos;
	}

	(void) memcpy(dest, src, nbytes);

	(void)px_rel(pxp->slave, from, 0);
	(void)px_rel(pxp, to, RGN_MODIFIED);
	
	return status;
}

static int
ncio_px_move(ncio *const nciop, off_t to, off_t from,
			size_t nbytes, int rflags)
{
	ncio_px *const pxp = (ncio_px *)nciop->pvt;
	int status = ENOERR;
	off_t lower;	
	off_t upper;
	char *base;
	size_t diff;
	size_t extent;

	if(to == from)
		return ENOERR; /* NOOP */
	
	if(fIsSet(rflags, RGN_WRITE) && !fIsSet(nciop->ioflags, NC_WRITE))
		return EPERM; /* attempt to write readonly file */

	rflags &= RGN_NOLOCK; /* filter unwanted flags */

	if(to > from)
	{
		/* growing */
		lower = from;	
		upper = to;
	}
	else
	{
		/* shrinking */
		lower = to;
		upper = from;
	}
	diff = (size_t)(upper - lower);
	extent = diff + nbytes;

#if INSTRUMENT
fprintf(stderr, "ncio_px_move %ld %ld %ld %ld %ld\n",
		 (long)to, (long)from, (long)nbytes, (long)lower, (long)extent);
#endif
	if(extent > pxp->blksz)
	{
		size_t remaining = nbytes;

if(to > from)
{
		off_t frm = from + nbytes;
		off_t toh = to + nbytes;
		for(;;)
		{
			size_t loopextent = MIN(remaining, pxp->blksz);
			frm -= loopextent;
			toh -= loopextent;

			status = px_double_buffer(nciop, toh, frm,
				 	loopextent, rflags) ;
			if(status != ENOERR)
				return status;
			remaining -= loopextent;

			if(remaining == 0)
				break; /* normal loop exit */
		}
}
else
{
		for(;;)
		{
			size_t loopextent = MIN(remaining, pxp->blksz);

			status = px_double_buffer(nciop, to, from,
				 	loopextent, rflags) ;
			if(status != ENOERR)
				return status;
			remaining -= loopextent;

			if(remaining == 0)
				break; /* normal loop exit */
			to += loopextent;
			from += loopextent;
		}
}
		return ENOERR;
	}
	
#if INSTRUMENT
fprintf(stderr, "\tncio_px_move small\n");
#endif
	status = px_get(nciop, pxp, lower, extent, RGN_WRITE|rflags,
			(void **)&base);

	if(status != ENOERR)
		return status;

	if(to > from)
		(void) memmove(base + diff, base, nbytes); 
	else
		(void) memmove(base, base + diff, nbytes); 
		
	(void) px_rel(pxp, lower, RGN_MODIFIED);

	return status;
}


static int
ncio_px_sync(ncio *const nciop)
{
	ncio_px *const pxp = (ncio_px *)nciop->pvt;
	int status = ENOERR;
	if(fIsSet(pxp->bf_rflags, RGN_MODIFIED))
	{
		assert(pxp->bf_refcount <= 0);
		status = px_pgout(nciop, pxp->bf_offset,
			pxp->bf_cnt,
			pxp->bf_base, &pxp->pos);
		if(status != ENOERR)
			return status;
		pxp->bf_rflags = 0;
	}
	return status;
}

static void
ncio_px_free(void *const pvt)
{
	ncio_px *const pxp = (ncio_px *)pvt;
	if(pxp == NULL)
		return;

	if(pxp->slave != NULL)
	{
		if(pxp->slave->bf_base != NULL)
		{
			free(pxp->slave->bf_base);
			pxp->slave->bf_base = NULL;
			pxp->slave->bf_extent = 0;
			pxp->slave->bf_offset = OFF_NONE;
		}
		free(pxp->slave);
		pxp->slave = NULL;
	}
		
	if(pxp->bf_base != NULL)
	{
		free(pxp->bf_base);
		pxp->bf_base = NULL;
		pxp->bf_extent = 0;
		pxp->bf_offset = OFF_NONE;
	}
}


static int
ncio_px_init2(ncio *const nciop, size_t *sizehintp, int isNew)
{
	ncio_px *const pxp = (ncio_px *)nciop->pvt;
	const size_t bufsz = 2 * *sizehintp;

	assert(nciop->fd >= 0);

	pxp->blksz = *sizehintp;

	assert(pxp->bf_base == NULL);

	/* this is separate allocation because it may grow */
	pxp->bf_base = malloc(bufsz);
	if(pxp->bf_base == NULL)
		return ENOMEM;
	/* else */
	pxp->bf_cnt = 0;
	if(isNew)
	{
		/* save a read */
		pxp->pos = 0;
		pxp->bf_offset = 0;
		pxp->bf_extent = bufsz;
		(void) memset(pxp->bf_base, 0, pxp->bf_extent);
	}
	return ENOERR;
}


static void
ncio_px_init(ncio *const nciop)
{
	ncio_px *const pxp = (ncio_px *)nciop->pvt;

	*((ncio_relfunc **)&nciop->rel) = ncio_px_rel; /* cast away const */
	*((ncio_getfunc **)&nciop->get) = ncio_px_get; /* cast away const */
	*((ncio_movefunc **)&nciop->move) = ncio_px_move; /* cast away const */
	*((ncio_syncfunc **)&nciop->sync) = ncio_px_sync; /* cast away const */
	*((ncio_freefunc **)&nciop->free) = ncio_px_free; /* cast away const */

	pxp->blksz = 0;
	pxp->pos = -1;
	pxp->bf_offset = OFF_NONE;
	pxp->bf_extent = 0;
	pxp->bf_rflags = 0;
	pxp->bf_refcount = 0;
	pxp->bf_base = NULL;
	pxp->slave = NULL;

}

/* Begin spx */

typedef struct ncio_spx {
	off_t pos;
	/* buffer */
	off_t	bf_offset; 
	size_t	bf_extent;
	size_t	bf_cnt;
	void	*bf_base;
} ncio_spx;


/*ARGSUSED*/
static int
ncio_spx_rel(ncio *const nciop, off_t offset, int rflags)
{
	ncio_spx *const pxp = (ncio_spx *)nciop->pvt;
	int status = ENOERR;

	assert(pxp->bf_offset <= offset);
	assert(pxp->bf_cnt != 0);
	assert(pxp->bf_cnt <= pxp->bf_extent);
#ifdef X_ALIGN
	assert(offset < pxp->bf_offset + X_ALIGN);
	assert(pxp->bf_cnt % X_ALIGN == 0 );
#endif

	if(fIsSet(rflags, RGN_MODIFIED))
	{
		if(!fIsSet(nciop->ioflags, NC_WRITE))
			return EPERM; /* attempt to write readonly file */

		status = px_pgout(nciop, pxp->bf_offset,
			pxp->bf_cnt,
			pxp->bf_base, &pxp->pos);
		/* if error, invalidate buffer anyway */
	}
	pxp->bf_offset = OFF_NONE;
	pxp->bf_cnt = 0;
	return status;
}


static int
ncio_spx_get(ncio *const nciop,
		off_t offset, size_t extent,
		int rflags,
		void **const vpp)
{
	ncio_spx *const pxp = (ncio_spx *)nciop->pvt;
	int status = ENOERR;
#ifdef X_ALIGN
	size_t rem;
#endif
	
	if(fIsSet(rflags, RGN_WRITE) && !fIsSet(nciop->ioflags, NC_WRITE))
		return EPERM; /* attempt to write readonly file */

	assert(extent != 0);
	assert(extent < X_INT_MAX); /* sanity check */
	assert(offset < X_INT_MAX); /* sanity check */

	assert(pxp->bf_cnt == 0);

#ifdef X_ALIGN
	rem = (size_t)(offset % X_ALIGN);
	if(rem != 0)
	{
		offset -= rem;
		extent += rem;
	}

	{
		const size_t rndup = extent % X_ALIGN;
		if(rndup != 0)
			extent += X_ALIGN - rndup;
	}

	assert(offset % X_ALIGN == 0);
	assert(extent % X_ALIGN == 0);
#endif

	if(pxp->bf_extent < extent)
	{
		if(pxp->bf_base != NULL)
		{
			free(pxp->bf_base);
			pxp->bf_base = NULL;
			pxp->bf_extent = 0;
		}
		assert(pxp->bf_extent == 0);
		pxp->bf_base = malloc(extent);
		if(pxp->bf_base == NULL)
			return ENOMEM;
		pxp->bf_extent = extent;
	}

	status = px_pgin(nciop, offset,
		 extent,
		 pxp->bf_base,
		 &pxp->bf_cnt, &pxp->pos);
	if(status != ENOERR)
		return status;

	pxp->bf_offset = offset;

	if(pxp->bf_cnt < extent)
		pxp->bf_cnt = extent;

#ifdef X_ALIGN
	*vpp = (char *)pxp->bf_base + rem;
#else
	*vpp = pxp->bf_base;
#endif
	return ENOERR;
}


#if 0
/*ARGSUSED*/
static int
strategy(ncio *const nciop, off_t to, off_t offset,
			size_t extent, int rflags)
{
	static ncio_spx pxp[1];
	int status = ENOERR;
#ifdef X_ALIGN
	size_t rem;
#endif
	
	assert(extent != 0);
	assert(extent < X_INT_MAX); /* sanity check */
	assert(offset < X_INT_MAX); /* sanity check */
#if INSTRUMENT
fprintf(stderr, "strategy %ld at %ld to %ld\n",
	 (long)extent, (long)offset, (long)to);
#endif


#ifdef X_ALIGN
	rem = (size_t)(offset % X_ALIGN);
	if(rem != 0)
	{
		offset -= rem;
		extent += rem;
	}

	{
		const size_t rndup = extent % X_ALIGN;
		if(rndup != 0)
			extent += X_ALIGN - rndup;
	}

	assert(offset % X_ALIGN == 0);
	assert(extent % X_ALIGN == 0);
#endif

	if(pxp->bf_extent < extent)
	{
		if(pxp->bf_base != NULL)
		{
			free(pxp->bf_base);
			pxp->bf_base = NULL;
			pxp->bf_extent = 0;
		}
		assert(pxp->bf_extent == 0);
		pxp->bf_base = malloc(extent);
		if(pxp->bf_base == NULL)
			return ENOMEM;
		pxp->bf_extent = extent;
	}

	status = px_pgin(nciop, offset,
		 extent,
		 pxp->bf_base,
		 &pxp->bf_cnt, &pxp->pos);
	if(status != ENOERR)
		return status;

	pxp->bf_offset = to; /* TODO: XALIGN */
	
	if(pxp->bf_cnt < extent)
		pxp->bf_cnt = extent;

	status = px_pgout(nciop, pxp->bf_offset,
		pxp->bf_cnt,
		pxp->bf_base, &pxp->pos);
	/* if error, invalidate buffer anyway */
	pxp->bf_offset = OFF_NONE;
	pxp->bf_cnt = 0;
	return status;
}
#endif

static int
ncio_spx_move(ncio *const nciop, off_t to, off_t from,
			size_t nbytes, int rflags)
{
	int status = ENOERR;
	off_t lower = from;	
	off_t upper = to;
	char *base;
	size_t diff = (size_t)(upper - lower);
	size_t extent = diff + nbytes;

	rflags &= RGN_NOLOCK; /* filter unwanted flags */

	if(to == from)
		return ENOERR; /* NOOP */
	
	if(to > from)
	{
		/* growing */
		lower = from;	
		upper = to;
	}
	else
	{
		/* shrinking */
		lower = to;
		upper = from;
	}

	diff = (size_t)(upper - lower);
	extent = diff + nbytes;

	status = ncio_spx_get(nciop, lower, extent, RGN_WRITE|rflags,
			(void **)&base);

	if(status != ENOERR)
		return status;

	if(to > from)
		(void) memmove(base + diff, base, nbytes); 
	else
		(void) memmove(base, base + diff, nbytes); 
		
	(void) ncio_spx_rel(nciop, lower, RGN_MODIFIED);

	return status;
}


/*ARGSUSED*/
static int
ncio_spx_sync(ncio *const nciop)
{
	/* NOOP */
	return ENOERR;
}

static void
ncio_spx_free(void *const pvt)
{
	ncio_spx *const pxp = (ncio_spx *)pvt;
	if(pxp == NULL)
		return;

	if(pxp->bf_base != NULL)
	{
		free(pxp->bf_base);
		pxp->bf_base = NULL;
		pxp->bf_offset = OFF_NONE;
		pxp->bf_extent = 0;
		pxp->bf_cnt = 0;
	}
}


static int
ncio_spx_init2(ncio *const nciop, const size_t *const sizehintp)
{
	ncio_spx *const pxp = (ncio_spx *)nciop->pvt;

	assert(nciop->fd >= 0);

	pxp->bf_extent = *sizehintp;

	assert(pxp->bf_base == NULL);

	/* this is separate allocation because it may grow */
	pxp->bf_base = malloc(pxp->bf_extent);
	if(pxp->bf_base == NULL)
	{
		pxp->bf_extent = 0;
		return ENOMEM;
	}
	/* else */
	return ENOERR;
}


static void
ncio_spx_init(ncio *const nciop)
{
	ncio_spx *const pxp = (ncio_spx *)nciop->pvt;

	*((ncio_relfunc **)&nciop->rel) = ncio_spx_rel; /* cast away const */
	*((ncio_getfunc **)&nciop->get) = ncio_spx_get; /* cast away const */
	*((ncio_movefunc **)&nciop->move) = ncio_spx_move; /* cast away const */
	*((ncio_syncfunc **)&nciop->sync) = ncio_spx_sync; /* cast away const */
	*((ncio_freefunc **)&nciop->free) = ncio_spx_free; /* cast away const */

	pxp->pos = -1;
	pxp->bf_offset = OFF_NONE;
	pxp->bf_extent = 0;
	pxp->bf_cnt = 0;
	pxp->bf_base = NULL;
}


/* */

static void
ncio_free(ncio *nciop)
{
	if(nciop == NULL)
		return;

	if(nciop->free != NULL)
		nciop->free(nciop->pvt);
	
	free(nciop);
}


static ncio *
ncio_new(const char *path, int ioflags)
{
	size_t sz_ncio = M_RNDUP(sizeof(ncio));
	size_t sz_path = M_RNDUP(strlen(path) +1);
	size_t sz_ncio_pvt;
	ncio *nciop;
 
#if ALWAYS_NC_SHARE /* DEBUG */
	fSet(ioflags, NC_SHARE);
#endif

	if(fIsSet(ioflags, NC_SHARE))
		sz_ncio_pvt = sizeof(ncio_spx);
	else
		sz_ncio_pvt = sizeof(ncio_px);

	nciop = (ncio *) malloc(sz_ncio + sz_path + sz_ncio_pvt);
	if(nciop == NULL)
		return NULL;
	
	nciop->ioflags = ioflags;
	*((int *)&nciop->fd) = -1; /* cast away const */

	nciop->path = (char *) ((char *)nciop + sz_ncio);
	(void) strcpy((char *)nciop->path, path); /* cast away const */

				/* cast away const */
	*((void **)&nciop->pvt) = (void *)(nciop->path + sz_path);

	if(fIsSet(ioflags, NC_SHARE))
		ncio_spx_init(nciop);
	else
		ncio_px_init(nciop);

	return nciop;
}


/* Public below this point */

#define NCIO_MINBLOCKSIZE 256
#define NCIO_MAXBLOCKSIZE 268435456 /* sanity check, about X_SIZE_T_MAX/8 */

#ifdef S_IRUSR
#define NC_DEFAULT_CREAT_MODE \
        (S_IRUSR|S_IWUSR|S_IRGRP|S_IWGRP|S_IROTH|S_IWOTH) /* 0666 */

#else
#define NC_DEFAULT_CREAT_MODE 0666
#endif

int
ncio_create(const char *path, int ioflags,
	size_t initialsz,
	off_t igeto, size_t igetsz, size_t *sizehintp,
	ncio **nciopp, void **const igetvpp)
{
	ncio *nciop;
	int oflags = (O_RDWR|O_CREAT);
	int fd;
	int status;

	if(initialsz < (size_t)igeto + igetsz)
		initialsz = (size_t)igeto + igetsz;

	fSet(ioflags, NC_WRITE);

	if(path == NULL || *path == 0)
		return EINVAL;

	nciop = ncio_new(path, ioflags);
	if(nciop == NULL)
		return ENOMEM;

	if(fIsSet(ioflags, NC_NOCLOBBER))
		fSet(oflags, O_EXCL);
	else
		fSet(oflags, O_TRUNC);
#ifdef O_BINARY
	fSet(oflags, O_BINARY);
#endif
#ifdef vms
	fd = open(path, oflags, NC_DEFAULT_CREAT_MODE, "ctx=stm");
#else
	/* Should we mess with the mode based on NC_SHARE ?? */
	fd = open(path, oflags, NC_DEFAULT_CREAT_MODE);
#endif
#if 0
	(void) fprintf(stderr, "ncio_create(): path=\"%s\"\n", path);
	(void) fprintf(stderr, "ncio_create(): oflags=0x%x\n", oflags);
#endif
	if(fd < 0)
	{
		status = errno;
		goto unwind_new;
	}
	*((int *)&nciop->fd) = fd; /* cast away const */

	if(*sizehintp < NCIO_MINBLOCKSIZE || *sizehintp > NCIO_MAXBLOCKSIZE)
	{
		/* Use default */
		*sizehintp = blksize(fd);
	}
	else
	{
		*sizehintp = M_RNDUP(*sizehintp);
	}

	if(fIsSet(nciop->ioflags, NC_SHARE))
		status = ncio_spx_init2(nciop, sizehintp);
	else
		status = ncio_px_init2(nciop, sizehintp, 1);

	if(status != ENOERR)
		goto unwind_open;

	if(initialsz != 0)
	{
		status = fgrow(fd, (off_t)initialsz);
		if(status != ENOERR)
			goto unwind_open;
	}

	if(igetsz != 0)
	{
		status = nciop->get(nciop,
				igeto, igetsz,
                        	RGN_WRITE,
                        	igetvpp);
		if(status != ENOERR)
			goto unwind_open;
	}

	*nciopp = nciop;
	return ENOERR;

unwind_open:
	(void) close(fd);
	/* ?? unlink */
	/*FALLTHRU*/
unwind_new:
	ncio_free(nciop);
	return status;
}


int
ncio_open(const char *path,
	int ioflags,
	off_t igeto, size_t igetsz, size_t *sizehintp,
	ncio **nciopp, void **const igetvpp)
{
	ncio *nciop;
	int oflags = fIsSet(ioflags, NC_WRITE) ? O_RDWR : O_RDONLY;
	int fd;
	int status;

	if(path == NULL || *path == 0)
		return EINVAL;

	nciop = ncio_new(path, ioflags);
	if(nciop == NULL)
		return ENOMEM;

#ifdef O_BINARY
	fSet(oflags, O_BINARY);
#endif
#ifdef vms
	fd = open(path, oflags, 0, "ctx=stm");
#else
	fd = open(path, oflags, 0);
#endif
	if(fd < 0)
	{
		status = errno;
		goto unwind_new;
	}
	*((int *)&nciop->fd) = fd; /* cast away const */

	if(*sizehintp < NCIO_MINBLOCKSIZE || *sizehintp > NCIO_MAXBLOCKSIZE)
	{
		/* Use default */
		*sizehintp = blksize(fd);
	}
	else
	{
		*sizehintp = M_RNDUP(*sizehintp);
	}

	if(fIsSet(nciop->ioflags, NC_SHARE))
		status = ncio_spx_init2(nciop, sizehintp);
	else
		status = ncio_px_init2(nciop, sizehintp, 0);

	if(status != ENOERR)
		goto unwind_open;

	if(igetsz != 0)
	{
		status = nciop->get(nciop,
				igeto, igetsz,
                        	0,
                        	igetvpp);
		if(status != ENOERR)
			goto unwind_open;
	}

	*nciopp = nciop;
	return ENOERR;

unwind_open:
	(void) close(fd);
	/*FALLTHRU*/
unwind_new:
	ncio_free(nciop);
	return status;
}


int 
ncio_close(ncio *nciop, int doUnlink)
{
	int status = ENOERR;

	if(nciop == NULL)
		return EINVAL;

	status = nciop->sync(nciop);

	(void) close(nciop->fd);
	
	if(doUnlink)
		(void) unlink(nciop->path);

	ncio_free(nciop);

	return status;
}