Update.

[glibc.git] / db2 / mp / mp_fget.c

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996, 1997, 1998
 *      Sleepycat Software.  All rights reserved.
 */
#include "config.h"

#ifndef lint
static const char sccsid[] = "@(#)mp_fget.c     10.48 (Sleepycat) 6/2/98";
#endif /* not lint */

#ifndef NO_SYSTEM_INCLUDES
#include <sys/types.h>

#include <errno.h>
#include <string.h>
#endif

#include "db_int.h"
#include "shqueue.h"
#include "db_shash.h"
#include "mp.h"
#include "common_ext.h"

/*
 * memp_fget --
 *      Get a page from the file.
 */
int
memp_fget(dbmfp, pgnoaddr, flags, addrp)
        DB_MPOOLFILE *dbmfp;
        db_pgno_t *pgnoaddr;
        u_int32_t flags;
        void *addrp;
{
        BH *bhp;
        DB_MPOOL *dbmp;
        MPOOL *mp;
        MPOOLFILE *mfp;
        size_t bucket, mf_offset;
        u_int32_t st_hsearch;
        int b_incr, first, ret;

        dbmp = dbmfp->dbmp;
        mp = dbmp->mp;
        mfp = dbmfp->mfp;

        /*
         * Validate arguments.
         *
         * !!!
         * Don't test for DB_MPOOL_CREATE and DB_MPOOL_NEW flags for readonly
         * files here, and create non-existent pages in readonly files if the
         * flags are set, later.  The reason is that the hash access method
         * wants to get empty pages that don't really exist in readonly files.
         * The only alternative is for hash to write the last "bucket" all the
         * time, which we don't want to do because one of our big goals in life
         * is to keep database files small.  It's sleazy as hell, but we catch
         * any attempt to actually write the file in memp_fput().
         */
#define OKFLAGS (DB_MPOOL_CREATE | DB_MPOOL_LAST | DB_MPOOL_NEW)
        if (flags != 0) {
                if ((ret =
                    __db_fchk(dbmp->dbenv, "memp_fget", flags, OKFLAGS)) != 0)
                        return (ret);

                switch (flags) {
                case DB_MPOOL_CREATE:
                case DB_MPOOL_LAST:
                case DB_MPOOL_NEW:
                case 0:
                        break;
                default:
                        return (__db_ferr(dbmp->dbenv, "memp_fget", 1));
                }
        }

#ifdef DIAGNOSTIC
        /*
         * XXX
         * We want to switch threads as often as possible.  Sleep every time
         * we get a new page to make it more likely.
         */
        if (DB_GLOBAL(db_pageyield) &&
            (__db_yield == NULL || __db_yield() != 0))
                __db_sleep(0, 1);
#endif

        /* Initialize remaining local variables. */
        mf_offset = R_OFFSET(dbmp, mfp);
        bhp = NULL;
        st_hsearch = 0;
        b_incr = ret = 0;

        /* Determine the hash bucket where this page will live. */
        bucket = BUCKET(mp, mf_offset, *pgnoaddr);

        LOCKREGION(dbmp);

        /*
         * Check for the last or last + 1 page requests.
         *
         * Examine and update the file's last_pgno value.  We don't care if
         * the last_pgno value immediately changes due to another thread --
         * at this instant in time, the value is correct.  We do increment the
         * current last_pgno value if the thread is asking for a new page,
         * however, to ensure that two threads creating pages don't get the
         * same one.
         */
        if (LF_ISSET(DB_MPOOL_LAST | DB_MPOOL_NEW)) {
                if (LF_ISSET(DB_MPOOL_NEW))
                        ++mfp->last_pgno;
                *pgnoaddr = mfp->last_pgno;
                bucket = BUCKET(mp, mf_offset, mfp->last_pgno);

                if (LF_ISSET(DB_MPOOL_NEW))
                        goto alloc;
        }

        /*
         * If mmap'ing the file and the page is not past the end of the file,
         * just return a pointer.
         *
         * The page may be past the end of the file, so check the page number
         * argument against the original length of the file.  If we previously
         * returned pages past the original end of the file, last_pgno will
         * have been updated to match the "new" end of the file, and checking
         * against it would return pointers past the end of the mmap'd region.
         *
         * If another process has opened the file for writing since we mmap'd
         * it, we will start playing the game by their rules, i.e. everything
         * goes through the cache.  All pages previously returned will be safe,
         * as long as the correct locking protocol was observed.
         *
         * XXX
         * We don't discard the map because we don't know when all of the
         * pages will have been discarded from the process' address space.
         * It would be possible to do so by reference counting the open
         * pages from the mmap, but it's unclear to me that it's worth it.
         */
        if (dbmfp->addr != NULL && F_ISSET(mfp, MP_CAN_MMAP)) {
                if (*pgnoaddr > mfp->orig_last_pgno) {
                        /*
                         * !!!
                         * See the comment above about non-existent pages and
                         * the hash access method.
                         */
                        if (!LF_ISSET(DB_MPOOL_CREATE)) {
                                __db_err(dbmp->dbenv,
                                    "%s: page %lu doesn't exist",
                                    __memp_fn(dbmfp), (u_long)*pgnoaddr);
                                ret = EINVAL;
                                goto err;
                        }
                } else {
                        *(void **)addrp =
                            R_ADDR(dbmfp, *pgnoaddr * mfp->stat.st_pagesize);
                        ++mp->stat.st_map;
                        ++mfp->stat.st_map;
                        goto done;
                }
        }

        /* Search the hash chain for the page. */
        for (bhp = SH_TAILQ_FIRST(&dbmp->htab[bucket], __bh);
            bhp != NULL; bhp = SH_TAILQ_NEXT(bhp, hq, __bh)) {
                ++st_hsearch;
                if (bhp->pgno != *pgnoaddr || bhp->mf_offset != mf_offset)
                        continue;

                /* Increment the reference count. */
                if (bhp->ref == UINT16_T_MAX) {
                        __db_err(dbmp->dbenv,
                            "%s: page %lu: reference count overflow",
                            __memp_fn(dbmfp), (u_long)bhp->pgno);
                        ret = EINVAL;
                        goto err;
                }

                /*
                 * Increment the reference count.  We may discard the region
                 * lock as we evaluate and/or read the buffer, so we need to
                 * ensure that it doesn't move and that its contents remain
                 * unchanged.
                 */
                ++bhp->ref;
                b_incr = 1;

                /*
                 * Any buffer we find might be trouble.
                 *
                 * BH_LOCKED --
                 * I/O is in progress.  Because we've incremented the buffer
                 * reference count, we know the buffer can't move.  Unlock
                 * the region lock, wait for the I/O to complete, and reacquire
                 * the region.
                 */
                for (first = 1; F_ISSET(bhp, BH_LOCKED); first = 0) {
                        UNLOCKREGION(dbmp);

                        /*
                         * Explicitly yield the processor if it's not the first
                         * pass through this loop -- if we don't, we might end
                         * up running to the end of our CPU quantum as we will
                         * simply be swapping between the two locks.
                         */
                        if (!first && (__db_yield == NULL || __db_yield() != 0))
                                __db_sleep(0, 1);

                        LOCKBUFFER(dbmp, bhp);
                        /* Wait for I/O to finish... */
                        UNLOCKBUFFER(dbmp, bhp);
                        LOCKREGION(dbmp);
                }

                /*
                 * BH_TRASH --
                 * The contents of the buffer are garbage.  Shouldn't happen,
                 * and this read is likely to fail, but might as well try.
                 */
                if (F_ISSET(bhp, BH_TRASH))
                        goto reread;

                /*
                 * BH_CALLPGIN --
                 * The buffer was converted so it could be written, and the
                 * contents need to be converted again.
                 */
                if (F_ISSET(bhp, BH_CALLPGIN)) {
                        if ((ret = __memp_pg(dbmfp, bhp, 1)) != 0)
                                goto err;
                        F_CLR(bhp, BH_CALLPGIN);
                }

                ++mp->stat.st_cache_hit;
                ++mfp->stat.st_cache_hit;
                *(void **)addrp = bhp->buf;
                goto done;
        }

alloc:  /* Allocate new buffer header and data space. */
        if ((ret = __memp_ralloc(dbmp, sizeof(BH) -
            sizeof(u_int8_t) + mfp->stat.st_pagesize, NULL, &bhp)) != 0)
                goto err;

#ifdef DIAGNOSTIC
        if ((ALIGNTYPE)bhp->buf & (sizeof(size_t) - 1)) {
                __db_err(dbmp->dbenv,
                    "Internal error: BH data NOT size_t aligned.");
                ret = EINVAL;
                goto err;
        }
#endif
        /* Initialize the BH fields. */
        memset(bhp, 0, sizeof(BH));
        LOCKINIT(dbmp, &bhp->mutex);
        bhp->ref = 1;
        bhp->pgno = *pgnoaddr;
        bhp->mf_offset = mf_offset;

        /*
         * Prepend the bucket header to the head of the appropriate MPOOL
         * bucket hash list.  Append the bucket header to the tail of the
         * MPOOL LRU chain.
         */
        SH_TAILQ_INSERT_HEAD(&dbmp->htab[bucket], bhp, hq, __bh);
        SH_TAILQ_INSERT_TAIL(&mp->bhq, bhp, q);

        /*
         * If we created the page, zero it out and continue.
         *
         * !!!
         * Note: DB_MPOOL_NEW specifically doesn't call the pgin function.
         * If DB_MPOOL_CREATE is used, then the application's pgin function
         * has to be able to handle pages of 0's -- if it uses DB_MPOOL_NEW,
         * it can detect all of its page creates, and not bother.
         *
         * Otherwise, read the page into memory, optionally creating it if
         * DB_MPOOL_CREATE is set.
         */
        if (LF_ISSET(DB_MPOOL_NEW)) {
                if (mfp->clear_len == 0)
                        memset(bhp->buf, 0, mfp->stat.st_pagesize);
                else {
                        memset(bhp->buf, 0, mfp->clear_len);
#ifdef DIAGNOSTIC
                        memset(bhp->buf + mfp->clear_len, 0xff,
                            mfp->stat.st_pagesize - mfp->clear_len);
#endif
                }

                ++mp->stat.st_page_create;
                ++mfp->stat.st_page_create;
        } else {
                /*
                 * It's possible for the read function to fail, which means
                 * that we fail as well.  Note, the __memp_pgread() function
                 * discards the region lock, so the buffer must be pinned
                 * down so that it cannot move and its contents are unchanged.
                 */
reread:         if ((ret = __memp_pgread(dbmfp,
                    bhp, LF_ISSET(DB_MPOOL_CREATE))) != 0) {
                        /*
                         * !!!
                         * Discard the buffer unless another thread is waiting
                         * on our I/O to complete.  Regardless, the header has
                         * the BH_TRASH flag set.
                         */
                        if (bhp->ref == 1)
                                __memp_bhfree(dbmp, mfp, bhp, 1);
                        goto err;
                }

                ++mp->stat.st_cache_miss;
                ++mfp->stat.st_cache_miss;
        }

        /*
         * If we're returning a page after our current notion of the last-page,
         * update our information.  Note, there's no way to un-instantiate this
         * page, it's going to exist whether it's returned to us dirty or not.
         */
        if (bhp->pgno > mfp->last_pgno)
                mfp->last_pgno = bhp->pgno;

        ++mp->stat.st_page_clean;
        *(void **)addrp = bhp->buf;

done:   /* Update the chain search statistics. */
        if (st_hsearch) {
                ++mp->stat.st_hash_searches;
                if (st_hsearch > mp->stat.st_hash_longest)
                        mp->stat.st_hash_longest = st_hsearch;
                mp->stat.st_hash_examined += st_hsearch;
        }

        UNLOCKREGION(dbmp);

        LOCKHANDLE(dbmp, dbmfp->mutexp);
        ++dbmfp->pinref;
        UNLOCKHANDLE(dbmp, dbmfp->mutexp);

        return (0);

err:    /* Discard our reference. */
        if (b_incr)
                --bhp->ref;
        UNLOCKREGION(dbmp);

        *(void **)addrp = NULL;
        return (ret);
}