hash_buf.c

Go to the documentation of this file.

/*-
 * 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);
}