xref: /csrg-svn/lib/libc/db/hash/hash_buf.c (revision 46562)

/*-
 * Copyright (c) 1990 The Regents of the University of California.
 * All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Margo Seltzer.
 *
 * %sccs.include.redist.c%
 */

#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)hash_buf.c	5.5 (Berkeley) 02/22/91";
#endif /* LIBC_SCCS and not lint */

/******************************************************************************

PACKAGE: hash

DESCRIPTION:
	Contains buffer management

ROUTINES:
    External
	__buf_init
	__get_buf
	__buf_free
	__reclaim_buf
    Internal
	newbuf

******************************************************************************/
#include <sys/types.h>
#include <assert.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include "hash.h"

/* Externals */
extern HTAB	*hashp;

/* My internals */
static BUFHEAD *newbuf();

/* Unlink B from its place in the lru */
#define BUF_REMOVE(B)			\
{					\
    B->prev->next = B->next;		\
    B->next->prev = B->prev;		\
}

/* Insert B after P */
#define BUF_INSERT(B,P)			\
{					\
    B->next = P->next;			\
    B->prev = P;			\
    P->next = B;			\
    B->next->prev = B;			\
}

#define	MRU	hashp->bufhead.next
#define	LRU	hashp->bufhead.prev

#define MRU_INSERT(B)	BUF_INSERT(B,(&hashp->bufhead))
#define LRU_INSERT(B)	BUF_INSERT(B,LRU)

/*
    We are looking for a buffer with address "addr".
    If prev_bp is NULL, then address is a bucket index.
    If prev_bp is not NULL, then it points to the page previous
	to an overflow page that we are trying to find.

    CAVEAT:  The buffer header accessed via prev_bp's ovfl field
    may no longer be valid.  Therefore, you must always verify that
    its address matches the address you are seeking.
*/
extern BUFHEAD *
__get_buf ( addr, prev_bp, newpage )
int	addr;
BUFHEAD	*prev_bp;
int	newpage;		/* If prev_bp is set, indicates that this is
					a new overflow page */
{
    register int	segment_ndx;
    register	BUFHEAD	*bp;
    register	unsigned	is_disk = 0;
    register	unsigned	is_disk_mask = 0;
    SEGMENT	segp;

    if ( prev_bp ) {
	bp = prev_bp->ovfl;
	if ( !bp || (bp->addr != addr) ) bp = NULL;
	if ( !newpage ) is_disk = BUF_DISK;
    }
    else {
	/* Grab buffer out of directory */
	segment_ndx = addr & ( hashp->SGSIZE - 1 );

	/*
	 * valid segment ensured by __call_hash()
	 */
	segp = hashp->dir[addr >> hashp->SSHIFT];
#ifdef DEBUG
	assert(segp != NULL);
#endif
	bp = PTROF(segp[segment_ndx]);
	is_disk_mask = ISDISK(segp[segment_ndx]);
	is_disk = is_disk_mask || !hashp->new_file;
    }

    if ( !bp ) {
	bp = newbuf ( addr, prev_bp );
	if ( !bp || __get_page ( bp->page, addr, !prev_bp, is_disk, 0 )) {
	    return(NULL);
	}
	if ( !prev_bp ) {
	    segp[segment_ndx] = (BUFHEAD *)((unsigned)bp | is_disk_mask );
	}
    } else {
	BUF_REMOVE ( bp );
	MRU_INSERT ( bp );
    }
    return(bp);
}

/*
    We need a buffer for this page. Either allocate one, or
    evict a resident one (if we have as many buffers as we're
    allowed) and put this one in.

    If newbuf finds an error (returning NULL), it also sets errno
*/
static BUFHEAD *
newbuf ( addr, prev_bp )
int	addr;
BUFHEAD	*prev_bp;
{
    register	BUFHEAD	*bp;	/* The buffer we're going to use */
    register	BUFHEAD	*xbp;	/* Temp pointer */
    register	BUFHEAD *next_xbp;
    int	segment_ndx;
    u_short	*shortp;
    u_short	oaddr;
    SEGMENT	segp;

    oaddr = 0;
    bp = LRU;
    /*
	If LRU buffer is pinned, the buffer pool is too small.
	We need to allocate more buffers
    */
    if ( hashp->nbufs || (bp->flags & BUF_PIN) ) {
	/* Allocate a new one */
	bp = (BUFHEAD *)malloc ( sizeof (struct _bufhead) );
	if ( !bp || !(bp->page = (char *)malloc ( hashp->BSIZE )) ) {
	    return (NULL);
	}
	hashp->nbufs--;
    } else {
	/* Kick someone out */
	BUF_REMOVE( bp );
	/*
	    If this is an overflow page with addr 0, it's already
	    been flushed back in an overflow chain and initialized
	*/
	if ( (bp->addr != 0) || (bp->flags & BUF_BUCKET) ) {
	    /*
		Set oaddr before __put_page so that you get it
		before bytes are swapped
	    */
	    shortp = (u_short *)bp->page;
	    if ( shortp[0] ) {
		oaddr = shortp[shortp[0]-1];
	    }
	    if ( (bp->flags & BUF_MOD) &&
		 __put_page(bp->page, bp->addr, (int)IS_BUCKET(bp->flags), 0) ) {
		return(NULL);
	    }
	    /*
		Update the pointer to this page (i.e. invalidate it).

		If this is a new file (i.e. we created it at open time),
		make sure that we mark pages which have been written to
		disk so we retrieve them from disk later, rather than
		allocating new pages.
	    */

	    if ( IS_BUCKET(bp->flags)) {
		segment_ndx = bp->addr & ( hashp->SGSIZE - 1 );

		segp = hashp->dir[bp->addr >> hashp->SSHIFT];

		assert(segp != NULL);

		if ( hashp->new_file &&
		     ((bp->flags & BUF_MOD) || ISDISK(segp[segment_ndx])) ) {
		    segp[segment_ndx] = (BUFHEAD *)BUF_DISK;
		} else segp[segment_ndx] = NULL;
	    }

	    /*
		Since overflow pages can only be access by means of
		their bucket, free overflow pages associated with this
		bucket.
	    */
	    for ( xbp = bp; xbp->ovfl; ) {

		next_xbp = xbp->ovfl;
		xbp->ovfl = 0;
		xbp = next_xbp;

		/* Check that ovfl pointer is up date */
		if ( IS_BUCKET(xbp->flags) || (oaddr != xbp->addr) ) break;

		shortp = (u_short *)xbp->page;
		if ( shortp[0] ) {
		    oaddr = shortp[shortp[0]-1];  /* set before __put_page */
		}
		if ( (xbp->flags & BUF_MOD) &&
		    __put_page ( xbp->page, xbp->addr, 0, 0 ) ) {
		    return(NULL);
		}
		xbp->addr = 0;
		xbp->flags = 0;
		BUF_REMOVE ( xbp );
		LRU_INSERT ( xbp );
	    }
	}
    }

    /* Now assign this buffer */
    bp->addr = addr;
#ifdef DEBUG1
    fprintf ( stderr, "NEWBUF1: %d->ovfl was %d is now %d\n", bp->addr,
		(bp->ovfl?bp->ovfl->addr:0),  0);
#endif
    bp->ovfl = NULL;
    if ( prev_bp ) {
	/*
	    If prev_bp is set, this is an overflow page, hook it in to the
	    buffer overflow links
	*/
#ifdef DEBUG1
	fprintf ( stderr, "NEWBUF2: %d->ovfl was %d is now %d\n", prev_bp->addr,
		    (prev_bp->ovfl?bp->ovfl->addr:0),
		    (bp?bp->addr: 0));
#endif
	prev_bp->ovfl = bp;
	bp->flags = 0;
    } else bp->flags = BUF_BUCKET;
    MRU_INSERT ( bp );
    return ( bp );
}

extern void
__buf_init ( nbytes )
int	nbytes;
{
    int	npages;
    BUFHEAD	*bfp = &(hashp->bufhead);

    npages = (nbytes + hashp->BSIZE - 1) >> hashp->BSHIFT;
    npages = MAX ( npages, MIN_BUFFERS );

    hashp->nbufs = npages;
    bfp->next = bfp;
    bfp->prev = bfp;
    /*
	This space is calloc'd so these are already null

	bfp->ovfl = NULL;
	bfp->flags = 0;
	bfp->page = NULL;
	bfp->addr = 0;
    */
}

extern int
__buf_free ( do_free, to_disk )
int	do_free;
int	to_disk;
{
    BUFHEAD	*bp;

    /* Need to make sure that buffer manager has been initialized */
    if ( !LRU ) {
	return(0);
    }

    for ( bp = LRU; bp != &hashp->bufhead; ) {
	/* Check that the buffer is valid */
	if ( bp->addr || IS_BUCKET(bp->flags) ) {
	    if ( to_disk && (bp->flags & BUF_MOD) &&
		 __put_page (bp->page, bp->addr, IS_BUCKET(bp->flags), 0 )) {
		return (-1);
	    }
	}

	/* Check if we are freeing stuff */
	if ( do_free ) {
	    if ( bp->page ) free ( bp->page );
	    BUF_REMOVE(bp);
	    (void)free ( bp );
	    bp = LRU;
	} else bp = bp->prev;
    }

    return(0);
}

extern void
__reclaim_buf ( bp )
BUFHEAD	*bp;
{
    bp->ovfl = 0;
    bp->addr = 0;
    bp->flags = 0;
    BUF_REMOVE ( bp );
    LRU_INSERT ( bp );
}