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);
}