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mp_bh.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_bh.c 10.45 (Sleepycat) 11/25/98";
#endif /* not lint */

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

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

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

static int __memp_upgrade __P((DB_MPOOL *, DB_MPOOLFILE *, MPOOLFILE *));

/*
 * __memp_bhwrite --
 *    Write the page associated with a given bucket header.
 *
 * PUBLIC: int __memp_bhwrite
 * PUBLIC:     __P((DB_MPOOL *, MPOOLFILE *, BH *, int *, int *));
 */
int
__memp_bhwrite(dbmp, mfp, bhp, restartp, wrotep)
      DB_MPOOL *dbmp;
      MPOOLFILE *mfp;
      BH *bhp;
      int *restartp, *wrotep;
{
      DB_MPOOLFILE *dbmfp;
      DB_MPREG *mpreg;
      int incremented, ret;

      if (restartp != NULL)
            *restartp = 0;
      if (wrotep != NULL)
            *wrotep = 0;
      incremented = 0;

      /*
       * Walk the process' DB_MPOOLFILE list and find a file descriptor for
       * the file.  We also check that the descriptor is open for writing.
       * If we find a descriptor on the file that's not open for writing, we
       * try and upgrade it to make it writeable.  If that fails, we're done.
       */
      LOCKHANDLE(dbmp, dbmp->mutexp);
      for (dbmfp = TAILQ_FIRST(&dbmp->dbmfq);
          dbmfp != NULL; dbmfp = TAILQ_NEXT(dbmfp, q))
            if (dbmfp->mfp == mfp) {
                  if (F_ISSET(dbmfp, MP_READONLY) &&
                      __memp_upgrade(dbmp, dbmfp, mfp)) {
                        UNLOCKHANDLE(dbmp, dbmp->mutexp);
                        return (0);
                  }

                  /*
                   * Increment the reference count -- see the comment in
                   * memp_fclose().
                   */
                  ++dbmfp->ref;
                  incremented = 1;
                  break;
            }
      UNLOCKHANDLE(dbmp, dbmp->mutexp);
      if (dbmfp != NULL)
            goto found;

      /*
       * It's not a page from a file we've opened.  If the file requires
       * input/output processing, see if this process has ever registered
       * information as to how to write this type of file.  If not, there's
       * nothing we can do.
       */
      if (mfp->ftype != 0) {
            LOCKHANDLE(dbmp, dbmp->mutexp);
            for (mpreg = LIST_FIRST(&dbmp->dbregq);
                mpreg != NULL; mpreg = LIST_NEXT(mpreg, q))
                  if (mpreg->ftype == mfp->ftype)
                        break;
            UNLOCKHANDLE(dbmp, dbmp->mutexp);
            if (mpreg == NULL)
                  return (0);
      }

      /*
       * Try and open the file, attaching to the underlying shared area.
       *
       * XXX
       * Don't try to attach to temporary files.  There are two problems in
       * trying to do that.  First, if we have different privileges than the
       * process that "owns" the temporary file, we might create the backing
       * disk file such that the owning process couldn't read/write its own
       * buffers, e.g., memp_trickle() running as root creating a file owned
       * as root, mode 600.  Second, if the temporary file has already been
       * created, we don't have any way of finding out what its real name is,
       * and, even if we did, it was already unlinked (so that it won't be
       * left if the process dies horribly).  This decision causes a problem,
       * however: if the temporary file consumes the entire buffer cache,
       * and the owner doesn't flush the buffers to disk, we could end up
       * with resource starvation, and the memp_trickle() thread couldn't do
       * anything about it.  That's a pretty unlikely scenario, though.
       *
       * XXX
       * There's no negative cache, so we may repeatedly try and open files
       * that we have previously tried (and failed) to open.
       *
       * Ignore any error, assume it's a permissions problem.
       */
      if (F_ISSET(mfp, MP_TEMP))
            return (0);

      if (__memp_fopen(dbmp, mfp, R_ADDR(dbmp, mfp->path_off),
          0, 0, mfp->stat.st_pagesize, 0, NULL, &dbmfp) != 0)
            return (0);

found:      ret = __memp_pgwrite(dbmfp, bhp, restartp, wrotep);

      if (incremented) {
            LOCKHANDLE(dbmp, dbmp->mutexp);
            --dbmfp->ref;
            UNLOCKHANDLE(dbmp, dbmp->mutexp);
      }

      return (ret);
}

/*
 * __memp_pgread --
 *    Read a page from a file.
 *
 * PUBLIC: int __memp_pgread __P((DB_MPOOLFILE *, BH *, int));
 */
int
__memp_pgread(dbmfp, bhp, can_create)
      DB_MPOOLFILE *dbmfp;
      BH *bhp;
      int can_create;
{
      DB_IO db_io;
      DB_MPOOL *dbmp;
      MPOOLFILE *mfp;
      size_t len, pagesize;
      ssize_t nr;
      int created, ret;

      dbmp = dbmfp->dbmp;
      mfp = dbmfp->mfp;
      pagesize = mfp->stat.st_pagesize;

      F_SET(bhp, BH_LOCKED | BH_TRASH);
      LOCKBUFFER(dbmp, bhp);
      UNLOCKREGION(dbmp);

      /*
       * Temporary files may not yet have been created.  We don't create
       * them now, we create them when the pages have to be flushed.
       */
      nr = 0;
      if (dbmfp->fd == -1)
            ret = 0;
      else {
            /*
             * Ignore read errors if we have permission to create the page.
             * Assume that the page doesn't exist, and that we'll create it
             * when we write it out.
             */
            db_io.fd_io = dbmfp->fd;
            db_io.fd_lock = dbmp->reginfo.fd;
            db_io.mutexp =
                F_ISSET(dbmp, MP_LOCKHANDLE) ? dbmfp->mutexp : NULL;
            db_io.pagesize = db_io.bytes = pagesize;
            db_io.pgno = bhp->pgno;
            db_io.buf = bhp->buf;

            ret = __os_io(&db_io, DB_IO_READ, &nr);
      }

      created = 0;
      if (nr < (ssize_t)pagesize)
            if (can_create)
                  created = 1;
            else {
                  /* If we had a short read, ret may be 0. */
                  if (ret == 0)
                        ret = EIO;
                  __db_err(dbmp->dbenv,
                      "%s: page %lu doesn't exist, create flag not set",
                      __memp_fn(dbmfp), (u_long)bhp->pgno);
                  goto err;
            }

      /*
       * Clear any bytes we didn't read that need to be cleared.  If we're
       * running in diagnostic mode, smash any bytes on the page that are
       * unknown quantities for the caller.
       */
      if (nr != (ssize_t)pagesize) {
            len = mfp->clear_len == 0 ? pagesize : mfp->clear_len;
            if (nr < (ssize_t)len)
                  memset(bhp->buf + nr, 0, len - nr);
#ifdef DIAGNOSTIC
            if (nr > (ssize_t)len)
                  len = nr;
            if (len < pagesize)
                  memset(bhp->buf + len, 0xdb, pagesize - len);
#endif
      }

      /* Call any pgin function. */
      ret = mfp->ftype == 0 ? 0 : __memp_pg(dbmfp, bhp, 1);

      /* Unlock the buffer and reacquire the region lock. */
err:  UNLOCKBUFFER(dbmp, bhp);
      LOCKREGION(dbmp);

      /*
       * If no errors occurred, the data is now valid, clear the BH_TRASH
       * flag; regardless, clear the lock bit and let other threads proceed.
       */
      F_CLR(bhp, BH_LOCKED);
      if (ret == 0) {
            F_CLR(bhp, BH_TRASH);

            /* Update the statistics. */
            if (created) {
                  ++dbmp->mp->stat.st_page_create;
                  ++mfp->stat.st_page_create;
            } else {
                  ++dbmp->mp->stat.st_page_in;
                  ++mfp->stat.st_page_in;
            }
      }

      return (ret);
}

/*
 * __memp_pgwrite --
 *    Write a page to a file.
 *
 * PUBLIC: int __memp_pgwrite __P((DB_MPOOLFILE *, BH *, int *, int *));
 */
int
__memp_pgwrite(dbmfp, bhp, restartp, wrotep)
      DB_MPOOLFILE *dbmfp;
      BH *bhp;
      int *restartp, *wrotep;
{
      DB_ENV *dbenv;
      DB_IO db_io;
      DB_LOG *lg_info;
      DB_LSN lsn;
      DB_MPOOL *dbmp;
      MPOOL *mp;
      MPOOLFILE *mfp;
      ssize_t nw;
      int callpgin, dosync, ret, syncfail;
      const char *fail;

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

      if (restartp != NULL)
            *restartp = 0;
      if (wrotep != NULL)
            *wrotep = 0;
      callpgin = 0;

      /*
       * Check the dirty bit -- this buffer may have been written since we
       * decided to write it.
       */
      if (!F_ISSET(bhp, BH_DIRTY)) {
            if (wrotep != NULL)
                  *wrotep = 1;
            return (0);
      }

      LOCKBUFFER(dbmp, bhp);

      /*
       * If there were two writers, we may have just been waiting while the
       * other writer completed I/O on this buffer.  Check the dirty bit one
       * more time.
       */
      if (!F_ISSET(bhp, BH_DIRTY)) {
            UNLOCKBUFFER(dbmp, bhp);

            if (wrotep != NULL)
                  *wrotep = 1;
            return (0);
      }

      F_SET(bhp, BH_LOCKED);
      UNLOCKREGION(dbmp);

      if (restartp != NULL)
            *restartp = 1;

      /* Copy the LSN off the page if we're going to need it. */
      lg_info = dbenv->lg_info;
      if (lg_info != NULL || F_ISSET(bhp, BH_WRITE))
            memcpy(&lsn, bhp->buf + mfp->lsn_off, sizeof(DB_LSN));

      /* Ensure the appropriate log records are on disk. */
      if (lg_info != NULL && (ret = log_flush(lg_info, &lsn)) != 0)
            goto err;

      /*
       * Call any pgout function.  We set the callpgin flag so that we flag
       * that the contents of the buffer will need to be passed through pgin
       * before they are reused.
       */
      if (mfp->ftype == 0)
            ret = 0;
      else {
            callpgin = 1;
            if ((ret = __memp_pg(dbmfp, bhp, 0)) != 0)
                  goto err;
      }

      /* Temporary files may not yet have been created. */
      if (dbmfp->fd == -1) {
            LOCKHANDLE(dbmp, dbmfp->mutexp);
            if (dbmfp->fd == -1 && ((ret = __db_appname(dbenv,
                DB_APP_TMP, NULL, NULL, DB_CREATE | DB_EXCL | DB_TEMPORARY,
                &dbmfp->fd, NULL)) != 0 || dbmfp->fd == -1)) {
                  UNLOCKHANDLE(dbmp, dbmfp->mutexp);
                  __db_err(dbenv,
                      "unable to create temporary backing file");
                  goto err;
            }
            UNLOCKHANDLE(dbmp, dbmfp->mutexp);
      }

      /* Write the page. */
      db_io.fd_io = dbmfp->fd;
      db_io.fd_lock = dbmp->reginfo.fd;
      db_io.mutexp = F_ISSET(dbmp, MP_LOCKHANDLE) ? dbmfp->mutexp : NULL;
      db_io.pagesize = db_io.bytes = mfp->stat.st_pagesize;
      db_io.pgno = bhp->pgno;
      db_io.buf = bhp->buf;
      if ((ret = __os_io(&db_io, DB_IO_WRITE, &nw)) != 0) {
            __db_panic(dbenv, ret);
            fail = "write";
            goto syserr;
      }
      if (nw != (ssize_t)mfp->stat.st_pagesize) {
            ret = EIO;
            fail = "write";
            goto syserr;
      }

      if (wrotep != NULL)
            *wrotep = 1;

      /* Unlock the buffer and reacquire the region lock. */
      UNLOCKBUFFER(dbmp, bhp);
      LOCKREGION(dbmp);

      /*
       * Clean up the flags based on a successful write.
       *
       * If we rewrote the page, it will need processing by the pgin
       * routine before reuse.
       */
      if (callpgin)
            F_SET(bhp, BH_CALLPGIN);
      F_CLR(bhp, BH_DIRTY | BH_LOCKED);

      /*
       * If we write a buffer for which a checkpoint is waiting, update
       * the count of pending buffers (both in the mpool as a whole and
       * for this file).  If the count for this file goes to zero, set a
       * flag so we flush the writes.
       */
      if (F_ISSET(bhp, BH_WRITE)) {
            F_CLR(bhp, BH_WRITE);

            --mp->lsn_cnt;
            dosync = --mfp->lsn_cnt == 0 ? 1 : 0;
      } else
            dosync = 0;

      /* Update the page clean/dirty statistics. */
      ++mp->stat.st_page_clean;
      --mp->stat.st_page_dirty;

      /* Update I/O statistics. */
      ++mp->stat.st_page_out;
      ++mfp->stat.st_page_out;

      /*
       * Do the sync after everything else has been updated, so any incoming
       * checkpoint doesn't see inconsistent information.
       *
       * XXX:
       * Don't lock the region around the sync, fsync(2) has no atomicity
       * issues.
       *
       * XXX:
       * We ignore errors from the sync -- it makes no sense to return an
       * error to the calling process, so set a flag causing the checkpoint
       * to be retried later.  There is a possibility, of course, that a
       * subsequent checkpoint was started and that we're going to force it
       * to fail.  That should be unlikely, and fixing it would be difficult.
       */
      if (dosync) {
            UNLOCKREGION(dbmp);
            syncfail = __os_fsync(dbmfp->fd) != 0;
            LOCKREGION(dbmp);
            if (syncfail)
                  F_SET(mp, MP_LSN_RETRY);
      }

      return (0);

syserr:     __db_err(dbenv, "%s: %s failed for page %lu",
          __memp_fn(dbmfp), fail, (u_long)bhp->pgno);

err:  /* Unlock the buffer and reacquire the region lock. */
      UNLOCKBUFFER(dbmp, bhp);
      LOCKREGION(dbmp);

      /*
       * Clean up the flags based on a failure.
       *
       * The page remains dirty but we remove our lock.  If we rewrote the
       * page, it will need processing by the pgin routine before reuse.
       */
      if (callpgin)
            F_SET(bhp, BH_CALLPGIN);
      F_CLR(bhp, BH_LOCKED);

      return (ret);
}

/*
 * __memp_pg --
 *    Call the pgin/pgout routine.
 *
 * PUBLIC: int __memp_pg __P((DB_MPOOLFILE *, BH *, int));
 */
int
__memp_pg(dbmfp, bhp, is_pgin)
      DB_MPOOLFILE *dbmfp;
      BH *bhp;
      int is_pgin;
{
      DBT dbt, *dbtp;
      DB_MPOOL *dbmp;
      DB_MPREG *mpreg;
      MPOOLFILE *mfp;
      int ftype, ret;

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

      LOCKHANDLE(dbmp, dbmp->mutexp);

      ftype = mfp->ftype;
      for (mpreg = LIST_FIRST(&dbmp->dbregq);
          mpreg != NULL; mpreg = LIST_NEXT(mpreg, q)) {
            if (ftype != mpreg->ftype)
                  continue;
            if (mfp->pgcookie_len == 0)
                  dbtp = NULL;
            else {
                  dbt.size = mfp->pgcookie_len;
                  dbt.data = R_ADDR(dbmp, mfp->pgcookie_off);
                  dbtp = &dbt;
            }
            UNLOCKHANDLE(dbmp, dbmp->mutexp);

            if (is_pgin) {
                  if (mpreg->pgin != NULL && (ret =
                      mpreg->pgin(bhp->pgno, bhp->buf, dbtp)) != 0)
                        goto err;
            } else
                  if (mpreg->pgout != NULL && (ret =
                      mpreg->pgout(bhp->pgno, bhp->buf, dbtp)) != 0)
                        goto err;
            break;
      }

      if (mpreg == NULL)
            UNLOCKHANDLE(dbmp, dbmp->mutexp);

      return (0);

err:  UNLOCKHANDLE(dbmp, dbmp->mutexp);
      __db_err(dbmp->dbenv, "%s: %s failed for page %lu",
          __memp_fn(dbmfp), is_pgin ? "pgin" : "pgout", (u_long)bhp->pgno);
      return (ret);
}

/*
 * __memp_bhfree --
 *    Free a bucket header and its referenced data.
 *
 * PUBLIC: void __memp_bhfree __P((DB_MPOOL *, MPOOLFILE *, BH *, int));
 */
void
__memp_bhfree(dbmp, mfp, bhp, free_mem)
      DB_MPOOL *dbmp;
      MPOOLFILE *mfp;
      BH *bhp;
      int free_mem;
{
      size_t off;

      /* Delete the buffer header from the hash bucket queue. */
      off = BUCKET(dbmp->mp, R_OFFSET(dbmp, mfp), bhp->pgno);
      SH_TAILQ_REMOVE(&dbmp->htab[off], bhp, hq, __bh);

      /* Delete the buffer header from the LRU queue. */
      SH_TAILQ_REMOVE(&dbmp->mp->bhq, bhp, q, __bh);

      /*
       * If we're not reusing it immediately, free the buffer header
       * and data for real.
       */
      if (free_mem) {
            __db_shalloc_free(dbmp->addr, bhp);
            --dbmp->mp->stat.st_page_clean;
      }
}

/*
 * __memp_upgrade --
 *    Upgrade a file descriptor from readonly to readwrite.
 */
static int
__memp_upgrade(dbmp, dbmfp, mfp)
      DB_MPOOL *dbmp;
      DB_MPOOLFILE *dbmfp;
      MPOOLFILE *mfp;
{
      int fd, ret;
      char *rpath;

      /*
       * !!!
       * We expect the handle to already be locked.
       */

      /* Check to see if we've already upgraded. */
      if (F_ISSET(dbmfp, MP_UPGRADE))
            return (0);

      /* Check to see if we've already failed. */
      if (F_ISSET(dbmfp, MP_UPGRADE_FAIL))
            return (1);

      /*
       * Calculate the real name for this file and try to open it read/write.
       * We know we have a valid pathname for the file because it's the only
       * way we could have gotten a file descriptor of any kind.
       */
      if ((ret = __db_appname(dbmp->dbenv, DB_APP_DATA,
          NULL, R_ADDR(dbmp, mfp->path_off), 0, NULL, &rpath)) != 0)
            return (ret);
      if (__db_open(rpath, 0, 0, 0, &fd) != 0) {
            F_SET(dbmfp, MP_UPGRADE_FAIL);
            ret = 1;
      } else {
            /* Swap the descriptors and set the upgrade flag. */
            (void)__os_close(dbmfp->fd);
            dbmfp->fd = fd;
            F_SET(dbmfp, MP_UPGRADE);
            ret = 0;
      }
      __os_freestr(rpath);
      return (ret);
}

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