# include	"../ingres.h"
# include	"../aux.h"
# include	"../unix.h"
# include	"../access.h"

/*
**  OPENCATALOG -- open system catalog
**
**	This routine opens a system catalog into a predetermined
**	cache.  If the catalog is already open, it is not reopened.
**
**	The 'Desxx' struct defines which relations may be opened
**	in this manner and is defined in .../source/aux.h.
**
**	The relation should not be closed after use (except in
**	special cases); however, it should be noclose'd after use
**	if the number of tuples in the catalog may have changed.
**
**	The Desxx structure has an alias field which
**	is the address of the 'Admin' structure cache which holds
**	the relation descriptor.  Thus, an openr need never actually
**	occur.
**
**	The actual desxx structure definition is in the file
**	
**		catalog_desc.c
**
**	which defines which relations can be cached and if any
**	alias descriptors exist for the relations. That file
**	can be redefined to include various caching.
**
**
**	Parameters:
**		name -- the name of the relation to open.  It must
**			match one of the names in the Desxx
**			structure.
**		mode -- just like 'mode' to openr.  If zero, it
**			is opened read-only; if two, it is opened
**			read/write.  In fact, the catalog is always
**			opened read/write, but the flags are set
**			right for concurrency to think that you are
**			using it as you have declared.
**
**	Returns:
**		none
**
**	Side Effects:
**		A relation is (may be) opened.
**
**	Requires:
**		Desxx -- a structure which defines the relations which
**			may be opened. A default structure is defined in
**			catalog_desc.c
**
**	Called By:
**		most dbu routines.
**		qrymod.
**		parser.
**		creatdb.
**
**	Trace Flags:
**		none
**
**	Diagnostics:
**		none
**
**	Syserrs:
**		opencatalog: (%s)
**			The indicated relation was not present in
**			the Desxx structure.
**		opencatalog: open(%s)
**			The indicated physical file could not be
**			opened.
**		opencatalog(%s): mode %d
**			You specified a bad mode (not 0 or 2).
**
**	History:
**		12/19/78 (epa) -- added a call to 'acc_init' if the
**			aliased form (avoiding an openr) is used.
**		12/12/78 (rse) -- structure definition moved to aux.h
**		10/6/78 (rse) -- catalog_desc.c broken off, and the
**			whole routine was moved to the utility library.
**		8/23/78 (eric) -- physical open of files dropped,
**			since we can reuse the file descriptors
**			from the Admin struct.
*/

int			Files[MAXFILES];

opencatalog(name, mode)
char	*name;
int	mode;
{
	int				i;
	register struct descriptor	*d;
	register char			*n;
	register struct desxx		*p;
	extern struct desxx		Desxx[];

	n = name;

	/* find out which descriptor it is */
	for (p = Desxx; p->cach_relname; p++)
		if (sequal(n, p->cach_relname))
			break;
	if (!p->cach_relname)
		syserr("opencatalog: (%s)", n);

	d = p->cach_desc;

	/* if it's already open, just return */
	if (d->relopn)
	{
		clearkeys(d);
	}
	else
	{
		/* not open, open it */
		if (p->cach_alias)
		{
			acc_init();
			bmove(p->cach_alias, d, sizeof (*d));
		}
		else
		{
			if ((i = openr(d, 2, n)) != 0)
				syserr("opencatalog: openr(%s) %d", n, i);
		}

		/* mark it as an open file */
		Files[d->relfp] = 0;
	}

	/* determine the mode to mark it as for concurrency */
	switch (mode)
	{
	  case 0:	/* read only */
		d->relopn = abs(d->relopn);
		break;

	  case 2:	/* read-write */
		d->relopn = -abs(d->relopn);
		break;

	  default:
		syserr("opencatalog(%s): mode %d", n, mode);
	}

	return;
}