hash_buf.c

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/*-
 * Copyright (c) 1990, 1993, 1994
 * The Regents of the University of California. All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Margo Seltzer.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 * notice, this list of conditions and the following disclaimer in the
 * documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 * must display the following acknowledgement:
 * This product includes software developed by the University of
 * California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 * may be used to endorse or promote products derived from this software
 * without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)hash_buf.c 8.5 (Berkeley) 7/15/94";
#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/param.h>

#include <errno.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>

#ifdef DEBUG
#include <assert.h>
#endif

#include "../include/db.h"
#include "hash.h"
#include "page.h"
#include "extern.h"

static BUFHEAD *newbuf __P((HTAB *, u_int32_t, BUFHEAD *));

/* 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(hashp, addr, prev_bp, newpage)
 HTAB *hashp;
 u_int32_t addr;
 BUFHEAD *prev_bp;
 int newpage; /* If prev_bp set, indicates a new overflow page. */
{
 register BUFHEAD *bp;
 register u_int32_t is_disk_mask;
 register int is_disk, segment_ndx = 0;
 SEGMENT segp = 0;

 is_disk = 0;
 is_disk_mask = 0;
 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(hashp, addr, prev_bp);
 if (!bp ||
 __get_page(hashp, bp->page, addr, !prev_bp, is_disk, 0))
 return (NULL);
 if (!prev_bp)
 segp[segment_ndx] =
 (BUFHEAD *)((ptrdiff_t)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(hashp, addr, prev_bp)
 HTAB *hashp;
 u_int32_t addr;
 BUFHEAD *prev_bp;
{
 register BUFHEAD *bp; /* The buffer we're going to use */
 register BUFHEAD *xbp; /* Temp pointer */
 register BUFHEAD *next_xbp;
 SEGMENT segp;
 int segment_ndx;
 u_int16_t oaddr, *shortp;

 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 */
 if ((bp = (BUFHEAD *)malloc(sizeof(BUFHEAD))) == NULL)
 return (NULL);
#ifdef PURIFY
 memset(bp, 0xff, sizeof(BUFHEAD));
#endif
 if ((bp->page = (char *)malloc(hashp->BSIZE)) == NULL) {
 free(bp);
 return (NULL);
 }
#ifdef PURIFY
 memset(bp->page, 0xff, hashp->BSIZE);
#endif
 if (hashp->nbufs)
 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_int16_t *)bp->page;
 if (shortp[0])
 oaddr = shortp[shortp[0] - 1];
 if ((bp->flags & BUF_MOD) && __put_page(hashp, 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];
#ifdef DEBUG
 assert(segp != NULL);
#endif

 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_int16_t *)xbp->page;
 if (shortp[0])
 /* set before __put_page */
 oaddr = shortp[shortp[0] - 1];
 if ((xbp->flags & BUF_MOD) && __put_page(hashp,
 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
 (void)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
 (void)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(hashp, nbytes)
 HTAB *hashp;
 int nbytes;
{
 BUFHEAD *bfp;
 int npages;

 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(hashp, do_free, to_disk)
 HTAB *hashp;
 int do_free, 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(hashp, 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);
 free(bp);
 bp = LRU;
 } else
 bp = bp->prev;
 }
 return (0);
}

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