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Sourcecode: db4.1 version File versions

log_put.c

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996-2002
 *    Sleepycat Software.  All rights reserved.
 */
#include "db_config.h"

#ifndef lint
static const char revid[] = "$Id: log_put.c,v 11.112 2002/09/10 02:39:26 bostic Exp $";
#endif /* not lint */

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

#if TIME_WITH_SYS_TIME
#include <sys/time.h>
#include <time.h>
#else
#if HAVE_SYS_TIME_H
#include <sys/time.h>
#else
#include <time.h>
#endif
#endif

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

#include "db_int.h"
#include "dbinc/crypto.h"
#include "dbinc/hmac.h"
#include "dbinc/log.h"
#include "dbinc/rep.h"
#include "dbinc/txn.h"

static int __log_encrypt_record __P((DB_ENV *, DBT *, HDR *, u_int32_t));
static int __log_fill __P((DB_LOG *, DB_LSN *, void *, u_int32_t));
static int __log_flush_commit __P((DB_ENV *, const DB_LSN *, u_int32_t));
static int __log_flush_int __P((DB_LOG *, const DB_LSN *, int));
static int __log_newfh __P((DB_LOG *));
static int __log_put_next __P((DB_ENV *,
    DB_LSN *, const DBT *, HDR *, DB_LSN *));
static int __log_putr __P((DB_LOG *,
    DB_LSN *, const DBT *, u_int32_t, HDR *));
static int __log_write __P((DB_LOG *, void *, u_int32_t));

/*
 * __log_put --
 *    Write a log record.  This is the public interface, DB_ENV->log_put.
 *
 * PUBLIC: int __log_put __P((DB_ENV *, DB_LSN *, const DBT *, u_int32_t));
 */
int
__log_put(dbenv, lsnp, udbt, flags)
      DB_ENV *dbenv;
      DB_LSN *lsnp;
      const DBT *udbt;
      u_int32_t flags;
{
      DB_CIPHER *db_cipher;
      DBT *dbt, t;
      DB_LOG *dblp;
      DB_LSN lsn, old_lsn;
      HDR hdr;
      LOG *lp;
      u_int32_t do_flush, op, writeonly;
      int lock_held, need_free, ret;
      u_int8_t *key;

      PANIC_CHECK(dbenv);
      ENV_REQUIRES_CONFIG(dbenv,
          dbenv->lg_handle, "DB_ENV->log_put", DB_INIT_LOG);

      /* Validate arguments. */
      op = DB_OPFLAGS_MASK & flags;
      if (op != 0 && op != DB_COMMIT)
            return (__db_ferr(dbenv, "DB_ENV->log_put", 0));

      /* Check for allowed bit-flags. */
      if (LF_ISSET(~(DB_OPFLAGS_MASK |
          DB_FLUSH | DB_NOCOPY | DB_PERMANENT | DB_WRNOSYNC)))
            return (__db_ferr(dbenv, "DB_ENV->log_put", 0));

      /* DB_WRNOSYNC and DB_FLUSH are mutually exclusive. */
      if (LF_ISSET(DB_WRNOSYNC) && LF_ISSET(DB_FLUSH))
            return (__db_ferr(dbenv, "DB_ENV->log_put", 1));

      /* Replication clients should never write log records. */
      if (F_ISSET(dbenv, DB_ENV_REP_CLIENT) ||
          F_ISSET(dbenv, DB_ENV_REP_LOGSONLY)) {
            __db_err(dbenv,
                "DB_ENV->log_put is illegal on replication clients");
            return (EINVAL);
      }

      dblp = dbenv->lg_handle;
      lp = dblp->reginfo.primary;
      db_cipher = dbenv->crypto_handle;
      dbt = &t;
      t = *udbt;
      lock_held = need_free = 0;
      do_flush = LF_ISSET(DB_FLUSH);
      writeonly = LF_ISSET(DB_WRNOSYNC);

      /*
       * If we are coming from the logging code, we use an internal
       * flag, DB_NOCOPY, because we know we can overwrite/encrypt
       * the log record in place.  Otherwise, if a user called log_put
       * then we must copy it to new memory so that we know we can
       * write it.
       *
       * We also must copy it to new memory if we are a replication
       * master so that we retain an unencrypted copy of the log
       * record to send to clients.
       */
      if (!LF_ISSET(DB_NOCOPY) || F_ISSET(dbenv, DB_ENV_REP_MASTER)) {
            if (CRYPTO_ON(dbenv))
                  t.size += db_cipher->adj_size(udbt->size);
            if ((ret = __os_calloc(dbenv, 1, t.size, &t.data)) != 0)
                  goto err;
            need_free = 1;
            memcpy(t.data, udbt->data, udbt->size);
      }
      if ((ret = __log_encrypt_record(dbenv, dbt, &hdr, udbt->size)) != 0)
            goto err;
      if (CRYPTO_ON(dbenv))
            key = db_cipher->mac_key;
      else
            key = NULL;
      /* Otherwise, we actually have a record to put.  Put it. */

      /* Before we grab the region lock, calculate the record's checksum. */
      __db_chksum(dbt->data, dbt->size, key, hdr.chksum);

      R_LOCK(dbenv, &dblp->reginfo);
      lock_held = 1;

      ZERO_LSN(old_lsn);
      if ((ret = __log_put_next(dbenv, &lsn, dbt, &hdr, &old_lsn)) != 0)
            goto err;

      if (F_ISSET(dbenv, DB_ENV_REP_MASTER)) {
            /*
             * Replication masters need to drop the lock to send
             * messages, but we want to drop and reacquire it a minimal
             * number of times.
             */
            R_UNLOCK(dbenv, &dblp->reginfo);
            lock_held = 0;

            /*
             * If we changed files and we're in a replicated
             * environment, we need to inform our clients now that
             * we've dropped the region lock.
             *
             * Note that a failed NEWFILE send is a dropped message
             * that our client can handle, so we can ignore it.  It's
             * possible that the record we already put is a commit, so
             * we don't just want to return failure.
             */
            if (!IS_ZERO_LSN(old_lsn))
                  (void)__rep_send_message(dbenv,
                      DB_EID_BROADCAST, REP_NEWFILE, &old_lsn, NULL, 0);

            /*
             * Then send the log record itself on to our clients.
             *
             * If the send fails and we're a commit or checkpoint,
             * there's nothing we can do;  the record's in the log.
             * Flush it, even if we're running with TXN_NOSYNC, on the
             * grounds that it should be in durable form somewhere.
             */
            /*
             * !!!
             * In the crypto case, we MUST send the udbt, not the
             * now-encrypted dbt.  Clients have no way to decrypt
             * without the header.
             */
            if ((__rep_send_message(dbenv,
                DB_EID_BROADCAST, REP_LOG, &lsn, udbt, flags) != 0) &&
                LF_ISSET(DB_PERMANENT))
                  do_flush |= DB_FLUSH;
      }

      /*
       * If needed, do a flush.  Note that failures at this point
       * are only permissible if we know we haven't written a commit
       * record;  __log_flush_commit is responsible for enforcing this.
       *
       * If a flush is not needed, see if WRITE_NOSYNC was set and we
       * need to write out the log buffer.
       */
      if (do_flush || writeonly) {
            if (!lock_held) {
                  R_LOCK(dbenv, &dblp->reginfo);
                  lock_held = 1;
            }
            if (do_flush)
                  ret = __log_flush_commit(dbenv, &lsn, flags);
            else if (lp->b_off != 0)
                  /*
                   * writeonly: if there's anything in the current
                   * log buffer, we need to write it out.
                   */
                  if ((ret = __log_write(dblp,
                      dblp->bufp, (u_int32_t)lp->b_off)) == 0)
                        lp->b_off = 0;
      }

err:  if (lock_held)
            R_UNLOCK(dbenv, &dblp->reginfo);
      if (need_free)
            __os_free(dbenv, dbt->data);

      if (ret == 0)
            *lsnp = lsn;

      return (ret);
}

/*
 * __log_txn_lsn --
 *
 * PUBLIC: void __log_txn_lsn
 * PUBLIC:     __P((DB_ENV *, DB_LSN *, u_int32_t *, u_int32_t *));
 */
void
__log_txn_lsn(dbenv, lsnp, mbytesp, bytesp)
      DB_ENV *dbenv;
      DB_LSN *lsnp;
      u_int32_t *mbytesp, *bytesp;
{
      DB_LOG *dblp;
      LOG *lp;

      dblp = dbenv->lg_handle;
      lp = dblp->reginfo.primary;

      R_LOCK(dbenv, &dblp->reginfo);

      /*
       * We are trying to get the LSN of the last entry in the log.  We use
       * this in two places: 1) DB_ENV->txn_checkpiont uses it as a first
       * value when trying to compute an LSN such that all transactions begun
       * before it are complete.   2) DB_ENV->txn_begin uses it as the
       * begin_lsn.
       *
       * Typically, it's easy to get the last written LSN, you simply look
       * at the current log pointer and back up the number of bytes of the
       * last log record.  However, if the last thing we did was write the
       * log header of a new log file, then, this doesn't work, so we return
       * the first log record that will be written in this new file.
       */
      *lsnp = lp->lsn;
      if (lp->lsn.offset > lp->len)
            lsnp->offset -= lp->len;

      /*
       * Since we're holding the log region lock, return the bytes put into
       * the log since the last checkpoint, transaction checkpoint needs it.
       *
       * We add the current buffer offset so as to count bytes that have not
       * yet been written, but are sitting in the log buffer.
       */
      if (mbytesp != NULL) {
            *mbytesp = lp->stat.st_wc_mbytes;
            *bytesp = (u_int32_t)(lp->stat.st_wc_bytes + lp->b_off);

            lp->stat.st_wc_mbytes = lp->stat.st_wc_bytes = 0;
      }

      R_UNLOCK(dbenv, &dblp->reginfo);
}

/*
 * __log_put_next --
 *    Put the given record as the next in the log, wherever that may
 * turn out to be.
 */
static int
__log_put_next(dbenv, lsn, dbt, hdr, old_lsnp)
      DB_ENV *dbenv;
      DB_LSN *lsn;
      const DBT *dbt;
      HDR *hdr;
      DB_LSN *old_lsnp;
{
      DB_LOG *dblp;
      DB_LSN old_lsn;
      LOG *lp;
      int newfile, ret;

      dblp = dbenv->lg_handle;
      lp = dblp->reginfo.primary;

      /*
       * Save a copy of lp->lsn before we might decide to switch log
       * files and change it.  If we do switch log files, and we're
       * doing replication, we'll need to tell our clients about the
       * switch, and they need to receive a NEWFILE message
       * with this "would-be" LSN in order to know they're not
       * missing any log records.
       */
      old_lsn = lp->lsn;
      newfile = 0;

      /*
       * If this information won't fit in the file, or if we're a
       * replication client environment and have been told to do so,
       * swap files.
       */
      if (lp->lsn.offset == 0 ||
          lp->lsn.offset + hdr->size + dbt->size > lp->log_size) {
            if (hdr->size + sizeof(LOGP) + dbt->size > lp->log_size) {
                  __db_err(dbenv,
                "DB_ENV->log_put: record larger than maximum file size");
                  return (EINVAL);
            }

            if ((ret = __log_newfile(dblp, NULL)) != 0)
                  return (ret);

            /*
             * Flag that we switched files, in case we're a master
             * and need to send this information to our clients.
             * We postpone doing the actual send until we can
             * safely release the log region lock and are doing so
             * anyway.
             */
            newfile = 1;
      }

      /*
       * The offset into the log file at this point is the LSN where
       * we're about to put this record, and is the LSN the caller wants.
       */
      *lsn = lp->lsn;

      /* If we switched log files, let our caller know where. */
      if (newfile)
            *old_lsnp = old_lsn;

      /* Actually put the record. */
      return (__log_putr(dblp, lsn, dbt, lp->lsn.offset - lp->len, hdr));
}

/*
 * __log_flush_commit --
 *    Flush a record for which the DB_FLUSH flag to log_put has been set.
 */
static int
__log_flush_commit(dbenv, lsnp, flags)
      DB_ENV *dbenv;
      const DB_LSN *lsnp;
      u_int32_t flags;
{
      DB_LOG *dblp;
      DB_LSN flush_lsn;
      LOG *lp;
      int ret;
      u_int32_t op;

      dblp = dbenv->lg_handle;
      lp = dblp->reginfo.primary;
      flush_lsn = *lsnp;
      op = DB_OPFLAGS_MASK & flags;

      if ((ret = __log_flush_int(dblp, &flush_lsn, 1)) == 0)
            return (0);

      /*
       * If a flush supporting a transaction commit fails, we must abort the
       * transaction.  (If we aren't doing a commit, return the failure; if
       * if the commit we care about made it to disk successfully, we just
       * ignore the failure, because there's no way to undo the commit.)
       */
      if (op != DB_COMMIT)
            return (ret);

      if (flush_lsn.file != lp->lsn.file || flush_lsn.offset < lp->w_off)
            return (0);

      /*
       * Else, make sure that the commit record does not get out after we
       * abort the transaction.  Do this by overwriting the commit record
       * in the buffer.  (Note that other commits in this buffer will wait
       * wait until a sucessful write happens, we do not wake them.)  We
       * point at the right part of the buffer and write an abort record
       * over the commit.  We must then try and flush the buffer again,
       * since the interesting part of the buffer may have actually made
       * it out to disk before there was a failure, we can't know for sure.
       */
      if (__txn_force_abort(dbenv,
          dblp->bufp + flush_lsn.offset - lp->w_off) == 0)
            (void)__log_flush_int(dblp, &flush_lsn, 0);

      return (ret);
}

/*
 * __log_newfile --
 *    Initialize and switch to a new log file.  (Note that this is
 * called both when no log yet exists and when we fill a log file.)
 *
 * PUBLIC: int __log_newfile __P((DB_LOG *, DB_LSN *));
 */
int
__log_newfile(dblp, lsnp)
      DB_LOG *dblp;
      DB_LSN *lsnp;
{
      DB_CIPHER *db_cipher;
      DB_ENV *dbenv;
      DB_LSN lsn;
      DBT t;
      HDR hdr;
      LOG *lp;
      int need_free, ret;
      u_int32_t lastoff;
      size_t tsize;
      u_int8_t *tmp;

      dbenv = dblp->dbenv;
      lp = dblp->reginfo.primary;

      /* If we're not at the beginning of a file already, start a new one. */
      if (lp->lsn.offset != 0) {
            /*
             * Flush the log so this file is out and can be closed.  We
             * cannot release the region lock here because we need to
             * protect the end of the file while we switch.  In
             * particular, a thread with a smaller record than ours
             * could detect that there is space in the log. Even
             * blocking that event by declaring the file full would
             * require all threads to wait here so that the lsn.file
             * can be moved ahead after the flush completes.  This
             * probably can be changed if we had an lsn for the
             * previous file and one for the curent, but it does not
             * seem like this would get much more throughput, if any.
             */
            if ((ret = __log_flush_int(dblp, NULL, 0)) != 0)
                  return (ret);

            DB_ASSERT(lp->b_off == 0);
            /*
             * Save the last known offset from the previous file, we'll
             * need it to initialize the persistent header information.
             */
            lastoff = lp->lsn.offset;

            /* Point the current LSN to the new file. */
            ++lp->lsn.file;
            lp->lsn.offset = 0;

            /* Reset the file write offset. */
            lp->w_off = 0;
      } else
            lastoff = 0;

      /*
       * Insert persistent information as the first record in every file.
       * Note that the previous length is wrong for the very first record
       * of the log, but that's okay, we check for it during retrieval.
       */
      DB_ASSERT(lp->b_off == 0);

      memset(&t, 0, sizeof(t));
      memset(&hdr, 0, sizeof(HDR));

      need_free = 0;
      tsize = sizeof(LOGP);
      db_cipher = dbenv->crypto_handle;
      if (CRYPTO_ON(dbenv))
            tsize += db_cipher->adj_size(tsize);
      if ((ret = __os_calloc(dbenv, 1, tsize, &tmp)) != 0)
            return (ret);
      lp->persist.log_size = lp->log_size = lp->log_nsize;
      memcpy(tmp, &lp->persist, sizeof(LOGP));
      t.data = tmp;
      t.size = (u_int32_t)tsize;
      need_free = 1;

      if ((ret =
          __log_encrypt_record(dbenv, &t, &hdr, (u_int32_t)tsize)) != 0)
            goto err;
      __db_chksum(t.data, t.size,
          (CRYPTO_ON(dbenv)) ? db_cipher->mac_key : NULL, hdr.chksum);
      lsn = lp->lsn;
      if ((ret = __log_putr(dblp, &lsn,
          &t, lastoff == 0 ? 0 : lastoff - lp->len, &hdr)) != 0)
            goto err;

      /* Update the LSN information returned to the caller. */
      if (lsnp != NULL)
            *lsnp = lp->lsn;

err:
      if (need_free)
            __os_free(dbenv, tmp);
      return (ret);
}

/*
 * __log_putr --
 *    Actually put a record into the log.
 */
static int
__log_putr(dblp, lsn, dbt, prev, h)
      DB_LOG *dblp;
      DB_LSN *lsn;
      const DBT *dbt;
      u_int32_t prev;
      HDR *h;
{
      DB_CIPHER *db_cipher;
      DB_ENV *dbenv;
      DB_LSN f_lsn;
      LOG *lp;
      HDR tmp, *hdr;
      int ret, t_ret;
      size_t b_off, nr;
      u_int32_t w_off;

      dbenv = dblp->dbenv;
      lp = dblp->reginfo.primary;

      /*
       * If we weren't given a header, use a local one.
       */
      db_cipher = dbenv->crypto_handle;
      if (h == NULL) {
            hdr = &tmp;
            memset(hdr, 0, sizeof(HDR));
            if (CRYPTO_ON(dbenv))
                  hdr->size = HDR_CRYPTO_SZ;
            else
                  hdr->size = HDR_NORMAL_SZ;
      } else
            hdr = h;

      /* Save our position in case we fail. */
      b_off = lp->b_off;
      w_off = lp->w_off;
      f_lsn = lp->f_lsn;

      /*
       * Initialize the header.  If we just switched files, lsn.offset will
       * be 0, and what we really want is the offset of the previous record
       * in the previous file.  Fortunately, prev holds the value we want.
       */
      hdr->prev = prev;
      hdr->len = (u_int32_t)hdr->size + dbt->size;

      /*
       * If we were passed in a nonzero checksum, our caller calculated
       * the checksum before acquiring the log mutex, as an optimization.
       *
       * If our caller calculated a real checksum of 0, we'll needlessly
       * recalculate it.  C'est la vie;  there's no out-of-bounds value
       * here.
       */
      if (hdr->chksum[0] == 0)
            __db_chksum(dbt->data, dbt->size,
                (CRYPTO_ON(dbenv)) ? db_cipher->mac_key : NULL,
                hdr->chksum);

      if ((ret = __log_fill(dblp, lsn, hdr, (u_int32_t)hdr->size)) != 0)
            goto err;

      if ((ret = __log_fill(dblp, lsn, dbt->data, dbt->size)) != 0)
            goto err;

      lp->len = (u_int32_t)(hdr->size + dbt->size);
      lp->lsn.offset += (u_int32_t)(hdr->size + dbt->size);
      return (0);
err:
      /*
       * If we wrote more than one buffer before failing, get the
       * first one back.  The extra buffers will fail the checksums
       * and be ignored.
       */
      if (w_off + lp->buffer_size < lp->w_off) {
            if ((t_ret =
                __os_seek(dbenv,
                &dblp->lfh, 0, 0, w_off, 0, DB_OS_SEEK_SET)) != 0 ||
                (t_ret = __os_read(dbenv, &dblp->lfh, dblp->bufp,
                b_off, &nr)) != 0)
                  return (__db_panic(dbenv, t_ret));
            if (nr != b_off) {
                  __db_err(dbenv, "Short read while restoring log");
                  return (__db_panic(dbenv, EIO));
            }
      }

      /* Reset to where we started. */
      lp->w_off = w_off;
      lp->b_off = b_off;
      lp->f_lsn = f_lsn;

      return (ret);
}

/*
 * __log_flush --
 *    Write all records less than or equal to the specified LSN.
 *
 * PUBLIC: int __log_flush __P((DB_ENV *, const DB_LSN *));
 */
int
__log_flush(dbenv, lsn)
      DB_ENV *dbenv;
      const DB_LSN *lsn;
{
      DB_LOG *dblp;
      int ret;

      PANIC_CHECK(dbenv);
      ENV_REQUIRES_CONFIG(dbenv,
          dbenv->lg_handle, "DB_ENV->log_flush", DB_INIT_LOG);

      dblp = dbenv->lg_handle;
      R_LOCK(dbenv, &dblp->reginfo);
      ret = __log_flush_int(dblp, lsn, 1);
      R_UNLOCK(dbenv, &dblp->reginfo);
      return (ret);
}

/*
 * __log_flush_int --
 *    Write all records less than or equal to the specified LSN; internal
 *    version.
 */
static int
__log_flush_int(dblp, lsnp, release)
      DB_LOG *dblp;
      const DB_LSN *lsnp;
      int release;
{
      DB_ENV *dbenv;
      DB_LSN flush_lsn, f_lsn;
      DB_MUTEX *flush_mutexp;
      LOG *lp;
      int current, do_flush, first, ret;
      size_t b_off;
      struct __db_commit *commit;
      u_int32_t ncommit, w_off;

      ret = 0;
      ncommit = 0;
      dbenv = dblp->dbenv;
      lp = dblp->reginfo.primary;
      flush_mutexp = R_ADDR(&dblp->reginfo, lp->flush_mutex_off);

      /*
       * If no LSN specified, flush the entire log by setting the flush LSN
       * to the last LSN written in the log.  Otherwise, check that the LSN
       * isn't a non-existent record for the log.
       */
      if (lsnp == NULL) {
            flush_lsn.file = lp->lsn.file;
            flush_lsn.offset = lp->lsn.offset - lp->len;
      } else if (lsnp->file > lp->lsn.file ||
          (lsnp->file == lp->lsn.file &&
          lsnp->offset > lp->lsn.offset - lp->len)) {
            __db_err(dbenv,
                "DB_ENV->log_flush: LSN past current end-of-log");
            return (EINVAL);
      } else {
            /*
             * See if we need to wait.  s_lsn is not locked so some
             * care is needed.  The sync point can only move forward.
             * If the file we want is in the past we are done.
             * If the file numbers are the same check the offset.
             * If this fails check the file numbers again since the
             * offset might have changed while we were looking.
             * This all assumes we can read an integer in one
             * state or the other, not in transition.
             */
            if (lp->s_lsn.file > lsnp->file)
                  return (0);

            if (lp->s_lsn.file == lsnp->file &&
                lp->s_lsn.offset > lsnp->offset)
                  return (0);

            if (lp->s_lsn.file > lsnp->file)
                  return (0);

            flush_lsn = *lsnp;
      }

      /*
       * If a flush is in progress and we're allowed to do so, drop
       * the region lock and block waiting for the next flush.
       */
      if (release && lp->in_flush != 0) {
            if ((commit = SH_TAILQ_FIRST(
                &lp->free_commits, __db_commit)) == NULL) {
                  if ((ret =
                      __db_shalloc(dblp->reginfo.addr,
                      sizeof(struct __db_commit),
                      MUTEX_ALIGN, &commit)) != 0)
                        goto flush;
                  memset(commit, 0, sizeof(*commit));
                  if ((ret = __db_mutex_setup(dbenv, &dblp->reginfo,
                      &commit->mutex, MUTEX_SELF_BLOCK |
                      MUTEX_NO_RLOCK)) != 0) {
                        __db_shalloc_free(dblp->reginfo.addr, commit);
                        return (ret);
                  }
                  MUTEX_LOCK(dbenv, &commit->mutex);
            } else
                  SH_TAILQ_REMOVE(
                      &lp->free_commits, commit, links, __db_commit);

            lp->ncommit++;

            /*
             * Flushes may be requested out of LSN order;  be
             * sure we only move lp->t_lsn forward.
             */
            if (log_compare(&lp->t_lsn, &flush_lsn) < 0)
                  lp->t_lsn = flush_lsn;

            commit->lsn = flush_lsn;
            SH_TAILQ_INSERT_HEAD(
                &lp->commits, commit, links, __db_commit);
            R_UNLOCK(dbenv, &dblp->reginfo);
            /* Wait here for the in-progress flush to finish. */
            MUTEX_LOCK(dbenv, &commit->mutex);
            R_LOCK(dbenv, &dblp->reginfo);

            lp->ncommit--;
            /*
             * Grab the flag before freeing the struct to see if
             * we need to flush the log to commit.  If so,
             * use the maximal lsn for any committing thread.
             */
            do_flush = F_ISSET(commit, DB_COMMIT_FLUSH);
            F_CLR(commit, DB_COMMIT_FLUSH);
            SH_TAILQ_INSERT_HEAD(
                &lp->free_commits, commit, links, __db_commit);
            if (do_flush) {
                  lp->in_flush--;
                  flush_lsn = lp->t_lsn;
            } else
                  return (0);
      }

      /*
       * Protect flushing with its own mutex so we can release
       * the region lock except during file switches.
       */
flush:      MUTEX_LOCK(dbenv, flush_mutexp);

      /*
       * If the LSN is less than or equal to the last-sync'd LSN, we're done.
       * Note, the last-sync LSN saved in s_lsn is the LSN of the first byte
       * after the byte we absolutely know was written to disk, so the test
       * is <, not <=.
       */
      if (flush_lsn.file < lp->s_lsn.file ||
          (flush_lsn.file == lp->s_lsn.file &&
          flush_lsn.offset < lp->s_lsn.offset)) {
            MUTEX_UNLOCK(dbenv, flush_mutexp);
            goto done;
      }

      /*
       * We may need to write the current buffer.  We have to write the
       * current buffer if the flush LSN is greater than or equal to the
       * buffer's starting LSN.
       */
      current = 0;
      if (lp->b_off != 0 && log_compare(&flush_lsn, &lp->f_lsn) >= 0) {
            if ((ret = __log_write(dblp,
                dblp->bufp, (u_int32_t)lp->b_off)) != 0) {
                  MUTEX_UNLOCK(dbenv, flush_mutexp);
                  goto done;
            }

            lp->b_off = 0;
            current = 1;
      }

      /*
       * It's possible that this thread may never have written to this log
       * file.  Acquire a file descriptor if we don't already have one.
       * One last check -- if we're not writing anything from the current
       * buffer, don't bother.  We have nothing to write and nothing to
       * sync.
       */
      if (!F_ISSET(&dblp->lfh, DB_FH_VALID) || dblp->lfname != lp->lsn.file)
            if (!current || (ret = __log_newfh(dblp)) != 0) {
                  MUTEX_UNLOCK(dbenv, flush_mutexp);
                  goto done;
            }

      /*
       * We are going to flush, release the region.
       * First get the current state of the buffer since
       * another write may come in, but we may not flush it.
       */
      b_off = lp->b_off;
      w_off = lp->w_off;
      f_lsn = lp->f_lsn;
      lp->in_flush++;
      if (release)
            R_UNLOCK(dbenv, &dblp->reginfo);

      /* Sync all writes to disk. */
      if ((ret = __os_fsync(dbenv, &dblp->lfh)) != 0) {
            MUTEX_UNLOCK(dbenv, flush_mutexp);
            if (release)
                  R_LOCK(dbenv, &dblp->reginfo);
            ret = __db_panic(dbenv, ret);
            return (ret);
      }

      /*
       * Set the last-synced LSN.
       * This value must be set to the LSN past the last complete
       * record that has been flushed.  This is at least the first
       * lsn, f_lsn.  If the buffer is empty, b_off == 0, then
       * we can move up to write point since the first lsn is not
       * set for the new buffer.
       */
      lp->s_lsn = f_lsn;
      if (b_off == 0)
            lp->s_lsn.offset = w_off;

      MUTEX_UNLOCK(dbenv, flush_mutexp);
      if (release)
            R_LOCK(dbenv, &dblp->reginfo);

      lp->in_flush--;
      ++lp->stat.st_scount;

      /*
       * How many flush calls (usually commits) did this call actually sync?
       * At least one, if it got here.
       */
      ncommit = 1;
done:
      if (lp->ncommit != 0) {
            first = 1;
            for (commit = SH_TAILQ_FIRST(&lp->commits, __db_commit);
                commit != NULL;
                commit = SH_TAILQ_NEXT(commit, links, __db_commit))
                  if (log_compare(&lp->s_lsn, &commit->lsn) > 0) {
                        MUTEX_UNLOCK(dbenv, &commit->mutex);
                        SH_TAILQ_REMOVE(
                            &lp->commits, commit, links, __db_commit);
                        ncommit++;
                  } else if (first == 1) {
                        F_SET(commit, DB_COMMIT_FLUSH);
                        MUTEX_UNLOCK(dbenv, &commit->mutex);
                        SH_TAILQ_REMOVE(
                            &lp->commits, commit, links, __db_commit);
                        /*
                         * This thread will wake and flush.
                         * If another thread commits and flushes
                         * first we will waste a trip trough the
                         * mutex.
                         */
                        lp->in_flush++;
                        first = 0;
                  }
      }
      if (lp->stat.st_maxcommitperflush < ncommit)
            lp->stat.st_maxcommitperflush = ncommit;
      if (lp->stat.st_mincommitperflush > ncommit ||
          lp->stat.st_mincommitperflush == 0)
            lp->stat.st_mincommitperflush = ncommit;

      return (ret);
}

/*
 * __log_fill --
 *    Write information into the log.
 */
static int
__log_fill(dblp, lsn, addr, len)
      DB_LOG *dblp;
      DB_LSN *lsn;
      void *addr;
      u_int32_t len;
{
      LOG *lp;
      u_int32_t bsize, nrec;
      size_t nw, remain;
      int ret;

      lp = dblp->reginfo.primary;
      bsize = lp->buffer_size;

      while (len > 0) {             /* Copy out the data. */
            /*
             * If we're beginning a new buffer, note the user LSN to which
             * the first byte of the buffer belongs.  We have to know this
             * when flushing the buffer so that we know if the in-memory
             * buffer needs to be flushed.
             */
            if (lp->b_off == 0)
                  lp->f_lsn = *lsn;

            /*
             * If we're on a buffer boundary and the data is big enough,
             * copy as many records as we can directly from the data.
             */
            if (lp->b_off == 0 && len >= bsize) {
                  nrec = len / bsize;
                  if ((ret = __log_write(dblp, addr, nrec * bsize)) != 0)
                        return (ret);
                  addr = (u_int8_t *)addr + nrec * bsize;
                  len -= nrec * bsize;
                  ++lp->stat.st_wcount_fill;
                  continue;
            }

            /* Figure out how many bytes we can copy this time. */
            remain = bsize - lp->b_off;
            nw = remain > len ? len : remain;
            memcpy(dblp->bufp + lp->b_off, addr, nw);
            addr = (u_int8_t *)addr + nw;
            len -= (u_int32_t)nw;
            lp->b_off += nw;

            /* If we fill the buffer, flush it. */
            if (lp->b_off == bsize) {
                  if ((ret = __log_write(dblp, dblp->bufp, bsize)) != 0)
                        return (ret);
                  lp->b_off = 0;
                  ++lp->stat.st_wcount_fill;
            }
      }
      return (0);
}

/*
 * __log_write --
 *    Write the log buffer to disk.
 */
static int
__log_write(dblp, addr, len)
      DB_LOG *dblp;
      void *addr;
      u_int32_t len;
{
      DB_ENV *dbenv;
      LOG *lp;
      size_t nw;
      int ret;

      dbenv = dblp->dbenv;
      lp = dblp->reginfo.primary;

      /*
       * If we haven't opened the log file yet or the current one
       * has changed, acquire a new log file.
       */
      if (!F_ISSET(&dblp->lfh, DB_FH_VALID) || dblp->lfname != lp->lsn.file)
            if ((ret = __log_newfh(dblp)) != 0)
                  return (ret);

      /*
       * Seek to the offset in the file (someone may have written it
       * since we last did).
       */
      if ((ret =
          __os_seek(dbenv,
          &dblp->lfh, 0, 0, lp->w_off, 0, DB_OS_SEEK_SET)) != 0 ||
          (ret = __os_write(dbenv, &dblp->lfh, addr, len, &nw)) != 0)
            return (ret);

      /* Reset the buffer offset and update the seek offset. */
      lp->w_off += len;

      /* Update written statistics. */
      if ((lp->stat.st_w_bytes += len) >= MEGABYTE) {
            lp->stat.st_w_bytes -= MEGABYTE;
            ++lp->stat.st_w_mbytes;
      }
      if ((lp->stat.st_wc_bytes += len) >= MEGABYTE) {
            lp->stat.st_wc_bytes -= MEGABYTE;
            ++lp->stat.st_wc_mbytes;
      }
      ++lp->stat.st_wcount;

      return (0);
}

/*
 * __log_file --
 *    Map a DB_LSN to a file name.
 *
 * PUBLIC: int __log_file __P((DB_ENV *, const DB_LSN *, char *, size_t));
 */
int
__log_file(dbenv, lsn, namep, len)
      DB_ENV *dbenv;
      const DB_LSN *lsn;
      char *namep;
      size_t len;
{
      DB_LOG *dblp;
      int ret;
      char *name;

      PANIC_CHECK(dbenv);
      ENV_REQUIRES_CONFIG(dbenv,
          dbenv->lg_handle, "DB_ENV->log_file", DB_INIT_LOG);

      dblp = dbenv->lg_handle;
      R_LOCK(dbenv, &dblp->reginfo);
      ret = __log_name(dblp, lsn->file, &name, NULL, 0);
      R_UNLOCK(dbenv, &dblp->reginfo);
      if (ret != 0)
            return (ret);

      /* Check to make sure there's enough room and copy the name. */
      if (len < strlen(name) + 1) {
            *namep = '\0';
            __db_err(dbenv, "DB_ENV->log_file: name buffer is too short");
            return (EINVAL);
      }
      (void)strcpy(namep, name);
      __os_free(dbenv, name);

      return (0);
}

/*
 * __log_newfh --
 *    Acquire a file handle for the current log file.
 */
static int
__log_newfh(dblp)
      DB_LOG *dblp;
{
      DB_ENV *dbenv;
      LOG *lp;
      int ret;
      char *name;

      dbenv = dblp->dbenv;
      lp = dblp->reginfo.primary;

      /* Close any previous file descriptor. */
      if (F_ISSET(&dblp->lfh, DB_FH_VALID))
            (void)__os_closehandle(dbenv, &dblp->lfh);

      /*
       * Get the path of the new file and open it.
       *
       * Adding DB_OSO_LOG to the flags may add additional platform-specific
       * optimizations.  On WinNT, the logfile is preallocated, which may
       * have a time penalty at startup, but have better overall throughput.
       * We are not certain that this works reliably, so enable at your own
       * risk.
       *
       * XXX:
       * Initialize the log file size.  This is a hack to push the log's
       * maximum size down into the Windows __os_open routine, because it
       * wants to pre-allocate it.
       */
      dblp->lfname = lp->lsn.file;
      dblp->lfh.log_size = lp->log_size;
      if ((ret = __log_name(dblp, dblp->lfname,
          &name, &dblp->lfh,
          DB_OSO_CREATE |/* DB_OSO_LOG |*/ DB_OSO_SEQ |
          (F_ISSET(dbenv, DB_ENV_DIRECT_LOG) ? DB_OSO_DIRECT : 0))) != 0)
            __db_err(dbenv,
                "DB_ENV->log_put: %s: %s", name, db_strerror(ret));

      __os_free(dbenv, name);
      return (ret);
}

/*
 * __log_name --
 *    Return the log name for a particular file, and optionally open it.
 *
 * PUBLIC: int __log_name __P((DB_LOG *,
 * PUBLIC:     u_int32_t, char **, DB_FH *, u_int32_t));
 */
int
__log_name(dblp, filenumber, namep, fhp, flags)
      DB_LOG *dblp;
      u_int32_t filenumber, flags;
      char **namep;
      DB_FH *fhp;
{
      DB_ENV *dbenv;
      LOG *lp;
      int ret;
      char *oname;
      char old[sizeof(LFPREFIX) + 5 + 20], new[sizeof(LFPREFIX) + 10 + 20];

      dbenv = dblp->dbenv;
      lp = dblp->reginfo.primary;

      /*
       * !!!
       * The semantics of this routine are bizarre.
       *
       * The reason for all of this is that we need a place where we can
       * intercept requests for log files, and, if appropriate, check for
       * both the old-style and new-style log file names.  The trick is
       * that all callers of this routine that are opening the log file
       * read-only want to use an old-style file name if they can't find
       * a match using a new-style name.  The only down-side is that some
       * callers may check for the old-style when they really don't need
       * to, but that shouldn't mess up anything, and we only check for
       * the old-style name when we've already failed to find a new-style
       * one.
       *
       * Create a new-style file name, and if we're not going to open the
       * file, return regardless.
       */
      (void)snprintf(new, sizeof(new), LFNAME, filenumber);
      if ((ret = __db_appname(dbenv,
          DB_APP_LOG, new, 0, NULL, namep)) != 0 || fhp == NULL)
            return (ret);

      /* Open the new-style file -- if we succeed, we're done. */
      if ((ret = __os_open(dbenv, *namep, flags, lp->persist.mode, fhp)) == 0)
            return (0);

      /*
       * The open failed... if the DB_RDONLY flag isn't set, we're done,
       * the caller isn't interested in old-style files.
       */
      if (!LF_ISSET(DB_OSO_RDONLY)) {
            __db_err(dbenv,
                "%s: log file open failed: %s", *namep, db_strerror(ret));
            return (__db_panic(dbenv, ret));
      }

      /* Create an old-style file name. */
      (void)snprintf(old, sizeof(old), LFNAME_V1, filenumber);
      if ((ret = __db_appname(dbenv, DB_APP_LOG, old, 0, NULL, &oname)) != 0)
            goto err;

      /*
       * Open the old-style file -- if we succeed, we're done.  Free the
       * space allocated for the new-style name and return the old-style
       * name to the caller.
       */
      if ((ret = __os_open(dbenv,
          oname, flags, lp->persist.mode, fhp)) == 0) {
            __os_free(dbenv, *namep);
            *namep = oname;
            return (0);
      }

      /*
       * Couldn't find either style of name -- return the new-style name
       * for the caller's error message.  If it's an old-style name that's
       * actually missing we're going to confuse the user with the error
       * message, but that implies that not only were we looking for an
       * old-style name, but we expected it to exist and we weren't just
       * looking for any log file.  That's not a likely error.
       */
err:  __os_free(dbenv, oname);
      return (ret);
}

/*
 * __log_rep_put --
 *    Short-circuit way for replication clients to put records into the
 * log.  Replication clients' logs need to be laid out exactly their masters'
 * are, so we let replication take responsibility for when the log gets
 * flushed, when log switches files, etc.  This is just a thin PUBLIC wrapper
 * for __log_putr with a slightly prettier interface.
 *
 * Note that the log region mutex should be held when this is called.
 *
 * PUBLIC: int __log_rep_put __P((DB_ENV *, DB_LSN *, const DBT *));
 */
int
__log_rep_put(dbenv, lsnp, rec)
      DB_ENV *dbenv;
      DB_LSN *lsnp;
      const DBT *rec;
{
      DB_CIPHER *db_cipher;
      DB_LOG *dblp;
      HDR hdr;
      DBT *dbt, t;
      LOG *lp;
      int need_free, ret;

      dblp = dbenv->lg_handle;
      lp = dblp->reginfo.primary;

      memset(&hdr, 0, sizeof(HDR));
      t = *rec;
      dbt = &t;
      need_free = 0;
      db_cipher = (DB_CIPHER *)dbenv->crypto_handle;
      if (CRYPTO_ON(dbenv))
            t.size += db_cipher->adj_size(rec->size);
      if ((ret = __os_calloc(dbenv, 1, t.size, &t.data)) != 0)
            goto err;
      need_free = 1;
      memcpy(t.data, rec->data, rec->size);

      if ((ret = __log_encrypt_record(dbenv, dbt, &hdr, rec->size)) != 0)
            goto err;
      __db_chksum(t.data, t.size,
          (CRYPTO_ON(dbenv)) ? db_cipher->mac_key : NULL, hdr.chksum);

      DB_ASSERT(log_compare(lsnp, &lp->lsn) == 0);
      ret = __log_putr(dblp, lsnp, dbt, lp->lsn.offset - lp->len, &hdr);
err:
      if (need_free)
            __os_free(dbenv, t.data);
      return (ret);
}

static int
__log_encrypt_record(dbenv, dbt, hdr, orig)
      DB_ENV *dbenv;
      DBT *dbt;
      HDR *hdr;
      u_int32_t orig;
{
      DB_CIPHER *db_cipher;
      int ret;

      if (CRYPTO_ON(dbenv)) {
            db_cipher = (DB_CIPHER *)dbenv->crypto_handle;
            hdr->size = HDR_CRYPTO_SZ;
            hdr->orig_size = orig;
            if ((ret = db_cipher->encrypt(dbenv, db_cipher->data,
                hdr->iv, dbt->data, dbt->size)) != 0)
                  return (ret);
      } else {
            hdr->size = HDR_NORMAL_SZ;
      }
      return (0);
}

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