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env_region.c

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996-2005
 *    Sleepycat Software.  All rights reserved.
 *
 * $Id: env_region.c,v 12.13 2005/10/21 19:13:01 bostic Exp $
 */

#include "db_config.h"

#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 <string.h>
#endif

#include "db_int.h"
#include "dbinc/db_shash.h"
#include "dbinc/crypto.h"
#include "dbinc/mp.h"

static void __db_des_destroy __P((DB_ENV *, REGION *));
static int  __db_des_get __P((DB_ENV *, REGINFO *, REGINFO *, REGION **));
static int  __db_e_remfile __P((DB_ENV *));
static int  __db_faultmem __P((DB_ENV *, void *, size_t, int));

/*
 * __db_e_attach
 *    Join/create the environment
 *
 * PUBLIC: int __db_e_attach __P((DB_ENV *, u_int32_t *));
 */
int
__db_e_attach(dbenv, init_flagsp)
      DB_ENV *dbenv;
      u_int32_t *init_flagsp;
{
      REGENV *renv;
      REGENV_REF ref;
      REGINFO *infop;
      REGION *rp, tregion;
      size_t size;
      size_t nrw;
      u_int32_t bytes, i, mbytes, nregions;
      u_int retry_cnt;
      int majver, minver, patchver, ret, segid;
      char buf[sizeof(DB_REGION_FMT) + 20];

      /* Initialization */
      retry_cnt = 0;

      /* Repeated initialization. */
loop: renv = NULL;

      /* Set up the DB_ENV's REG_INFO structure. */
      if ((ret = __os_calloc(dbenv, 1, sizeof(REGINFO), &infop)) != 0)
            return (ret);
      infop->dbenv = dbenv;
      infop->type = REGION_TYPE_ENV;
      infop->id = REGION_ID_ENV;
      infop->flags = REGION_JOIN_OK;
      if (F_ISSET(dbenv, DB_ENV_CREATE))
            F_SET(infop, REGION_CREATE_OK);

      /*
       * We have to single-thread the creation of the REGENV region.  Once
       * it exists, we can serialize using region mutexes, but until then
       * we have to be the only player in the game.
       *
       * If this is a private environment, we are only called once and there
       * are no possible race conditions.
       *
       * If this is a public environment, we use the filesystem to ensure
       * the creation of the environment file is single-threaded.
       */
      if (F_ISSET(dbenv, DB_ENV_PRIVATE)) {
            if ((ret = __os_strdup(dbenv,
                "process-private", &infop->name)) != 0)
                  goto err;
            goto creation;
      }

      /* Build the region name. */
      (void)snprintf(buf, sizeof(buf), "%s", DB_REGION_ENV);
      if ((ret = __db_appname(dbenv,
          DB_APP_NONE, buf, 0, NULL, &infop->name)) != 0)
            goto err;

      /*
       * Try to create the file, if we have the authority.  We have to ensure
       * that multiple threads/processes attempting to simultaneously create
       * the file are properly ordered.  Open using the O_CREAT and O_EXCL
       * flags so that multiple attempts to create the region will return
       * failure in all but one.  POSIX 1003.1 requires that EEXIST be the
       * errno return value -- I sure hope they're right.
       */
      if (F_ISSET(dbenv, DB_ENV_CREATE)) {
            if ((ret = __os_open(dbenv, infop->name,
                DB_OSO_CREATE | DB_OSO_EXCL | DB_OSO_REGION,
                dbenv->db_mode, &dbenv->lockfhp)) == 0)
                  goto creation;
            if (ret != EEXIST) {
                  __db_err(dbenv,
                      "%s: %s", infop->name, db_strerror(ret));
                  goto err;
            }
      }

      /*
       * If we couldn't create the file, try and open it.  (If that fails,
       * we're done.)
       */
      if ((ret = __os_open(
          dbenv, infop->name, DB_OSO_REGION, 0, &dbenv->lockfhp)) != 0)
            goto err;

      /* The region exists, it's not okay to recreate it. */
      F_CLR(infop, REGION_CREATE_OK);

      /*
       * !!!
       * The region may be in system memory not backed by the filesystem
       * (more specifically, not backed by this file), and we're joining
       * it.  In that case, the process that created it will have written
       * out a REGENV_REF structure as its only contents.  We read that
       * structure before we do anything further, e.g., we can't just map
       * that file in and then figure out what's going on.
       *
       * All of this noise is because some systems don't have a coherent VM
       * and buffer cache, and what's worse, when you mix operations on the
       * VM and buffer cache, half the time you hang the system.
       *
       * If the file is the size of an REGENV_REF structure, then we know
       * the real region is in some other memory.  (The only way you get a
       * file that size is to deliberately write it, as it's smaller than
       * any possible disk sector created by writing a file or mapping the
       * file into memory.)  In which case, retrieve the structure from the
       * file and use it to acquire the referenced memory.
       *
       * If the structure is larger than a REGENV_REF structure, then this
       * file is backing the shared memory region, and we just map it into
       * memory.
       *
       * And yes, this makes me want to take somebody and kill them.  (I
       * digress -- but you have no freakin' idea.  This is unbelievably
       * stupid and gross, and I've probably spent six months of my life,
       * now, trying to make different versions of it work.)
       */
      if ((ret = __os_ioinfo(dbenv, infop->name,
          dbenv->lockfhp, &mbytes, &bytes, NULL)) != 0) {
            __db_err(dbenv, "%s: %s", infop->name, db_strerror(ret));
            goto err;
      }

      /*
       * !!!
       * A size_t is OK -- regions get mapped into memory, and so can't
       * be larger than a size_t.
       */
      size = mbytes * MEGABYTE + bytes;

      /*
       * If the size is less than the size of a REGENV_REF structure, the
       * region (or, possibly, the REGENV_REF structure) has not yet been
       * completely written.  Shouldn't be possible, but there's no reason
       * not to wait awhile and try again.
       *
       * Otherwise, if the size is the size of a REGENV_REF structure,
       * read it into memory and use it as a reference to the real region.
       */
      if (size <= sizeof(ref)) {
            if (size != sizeof(ref))
                  goto retry;

            if ((ret = __os_read(dbenv, dbenv->lockfhp, &ref,
                sizeof(ref), &nrw)) != 0 || nrw < (size_t)sizeof(ref)) {
                  if (ret == 0)
                        ret = EIO;
                  __db_err(dbenv,
                "%s: unable to read system-memory information from: %s",
                      infop->name, db_strerror(ret));
                  goto err;
            }
            size = ref.size;
            segid = ref.segid;

            F_SET(dbenv, DB_ENV_SYSTEM_MEM);
      } else if (F_ISSET(dbenv, DB_ENV_SYSTEM_MEM)) {
            ret = EINVAL;
            __db_err(dbenv,
                "%s: existing environment not created in system memory: %s",
                infop->name, db_strerror(ret));
            goto err;
      } else
            segid = INVALID_REGION_SEGID;

#ifndef HAVE_MUTEX_FCNTL
      /*
       * If we're not doing fcntl locking, we can close the file handle.  We
       * no longer need it and the less contact between the buffer cache and
       * the VM, the better.
       */
       (void)__os_closehandle(dbenv, dbenv->lockfhp);
       dbenv->lockfhp = NULL;
#endif

      /* Call the region join routine to acquire the region. */
      memset(&tregion, 0, sizeof(tregion));
      tregion.size = (roff_t)size;
      tregion.segid = segid;
      if ((ret = __os_r_attach(dbenv, infop, &tregion)) != 0)
            goto err;

      /*
       * The environment's REGENV structure has to live at offset 0 instead
       * of the usual shalloc information.  Set the primary reference and
       * correct the "addr" value to reference the shalloc region.  Note,
       * this means that all of our offsets (R_ADDR/R_OFFSET) get shifted
       * as well, but that should be fine.
       */
      infop->primary = infop->addr;
      infop->addr = (u_int8_t *)infop->addr + sizeof(REGENV);
      renv = infop->primary;

      /*
       * Make sure the region matches our build.  Special case a region
       * that's all nul bytes, just treat it like any other corruption.
       *
       * !!!
       * We don't display the major/minor version from the environment,
       * because it may be in a different place in the two regions.
       */
      if (renv->majver != DB_VERSION_MAJOR ||
          renv->minver != DB_VERSION_MINOR) {
            if (renv->majver != 0 || renv->minver != 0) {
                  __db_err(dbenv,
      "Program version %d.%d doesn't match environment version %d.%d",
                      DB_VERSION_MAJOR, DB_VERSION_MINOR,
                      renv->majver, renv->minver);
                  ret = DB_VERSION_MISMATCH;
            } else
                  ret = EINVAL;
            goto err;
      }

      /*
       * Check if the environment has had a catastrophic failure.
       *
       * Check the magic number to ensure the region is initialized.  If the
       * magic number isn't set, the lock may not have been initialized, and
       * an attempt to use it could lead to random behavior.
       *
       * The panic and magic values aren't protected by any lock, so we never
       * use them in any check that's more complex than set/not-set.
       *
       * !!!
       * I'd rather play permissions games using the underlying file, but I
       * can't because Windows/NT filesystems won't open files mode 0.
       */
      if (renv->panic && !F_ISSET(dbenv, DB_ENV_NOPANIC)) {
            ret = __db_panic_msg(dbenv);
            goto err;
      }
      if (renv->magic != DB_REGION_MAGIC)
            goto retry;

      /*
       * Get a reference to the underlying REGION information for this
       * environment.
       */
      if ((ret = __db_des_get(dbenv, infop, infop, &rp)) != 0 || rp == NULL)
            goto find_err;
      infop->rp = rp;

      /*
       * There's still a possibility for inconsistent data.  When we acquired
       * the size of the region and attached to it, it might have still been
       * growing as part of its creation.  We can detect this by checking the
       * size we originally found against the region's current size.  (The
       * region's current size has to be final, the creator finished growing
       * it before setting the magic number in the region.)
       */
      if (rp->size != size)
            goto retry;

      /* Increment the reference count. */
      MUTEX_LOCK(dbenv, renv->mtx_regenv);
      ++renv->refcnt;
      MUTEX_UNLOCK(dbenv, renv->mtx_regenv);

      /*
       * Check our callers configuration flags, it's an error to configure
       * incompatible or additional subsystems in an existing environment.
       * Return the total set of flags to the caller so they initialize the
       * correct set of subsystems.
       */
      if (init_flagsp != NULL) {
            FLD_CLR(*init_flagsp, renv->init_flags);
            if (*init_flagsp != 0) {
                  __db_err(dbenv,
    "configured environment flags incompatible with existing environment");
                  ret = EINVAL;
                  goto err;
            }
            *init_flagsp = renv->init_flags;
      }

      /*
       * Fault the pages into memory.  Note, do this AFTER releasing the
       * lock, because we're only reading the pages, not writing them.
       */
      (void)__db_faultmem(dbenv, infop->primary, rp->size, 0);

      /* Everything looks good, we're done. */
      dbenv->reginfo = infop;
      return (0);

creation:
      /* Create the environment region. */
      F_SET(infop, REGION_CREATE);

      /*
       * Allocate room for REGION structures plus overhead.
       *
       * XXX
       * Overhead is so high because encryption passwds are stored in the
       * base environment region, as are replication vote arrays.  This is
       * a bug, not a feature, replication needs its own region.
       */
      memset(&tregion, 0, sizeof(tregion));
      nregions = dbenv->mp_ncache + 10;
      tregion.size =
         (roff_t)(nregions * sizeof(REGION) + dbenv->passwd_len + 16 * 1024);
      tregion.segid = INVALID_REGION_SEGID;
      if ((ret = __os_r_attach(dbenv, infop, &tregion)) != 0)
            goto err;

      /*
       * Fault the pages into memory.  Note, do this BEFORE we initialize
       * anything, because we're writing the pages, not just reading them.
       */
      (void)__db_faultmem(dbenv, infop->addr, tregion.size, 1);

      /*
       * The first object in the region is the REGENV structure.  This is
       * different from the other regions, and, from everything else in
       * this region, where all objects are allocated from the pool, i.e.,
       * there aren't any fixed locations.  The remaining space is made
       * available for later allocation.
       *
       * The allocation space must be size_t aligned, because that's what
       * the initialization routine is going to store there.  To make sure
       * that happens, the REGENV structure was padded with a final size_t.
       * No other region needs to worry about it because all of them treat
       * the entire region as allocation space.
       *
       * Set the primary reference and correct the "addr" value to reference
       * the shalloc region.  Note, this requires that we "uncorrect" it at
       * region detach, and that all of our offsets (R_ADDR/R_OFFSET) will be
       * shifted as well, but that should be fine.
       */
      infop->primary = infop->addr;
      infop->addr = (u_int8_t *)infop->addr + sizeof(REGENV);
      __db_shalloc_init(infop, tregion.size - sizeof(REGENV));

      /*
       * Initialize the rest of the REGENV structure.  (Don't set the magic
       * number to the correct value, that would validate the environment).
       */
      renv = infop->primary;
      renv->magic = 0;
      renv->panic = 0;

      (void)db_version(&majver, &minver, &patchver);
      renv->majver = (u_int32_t)majver;
      renv->minver = (u_int32_t)minver;
      renv->patchver = (u_int32_t)patchver;

      (void)time(&renv->timestamp);
      __os_unique_id(dbenv, &renv->envid);

      if ((ret = __mutex_alloc(
          dbenv, MTX_ENV_REGION, 0, &renv->mtx_regenv)) != 0)
            goto err;
      renv->refcnt = 1;

      /*
       * Initialize init_flags to store the flags that any other environment
       * handle that uses DB_JOINENV to join this environment will need.
       */
      renv->init_flags = (init_flagsp == NULL) ? 0 : *init_flagsp;

      /*
       * Set up the region array.  We use an array rather than a linked list
       * as we have to traverse this list after failure in some cases, and
       * we don't want to infinitely loop should the application fail while
       * we're manipulating the list.
       */
      renv->region_cnt = nregions;
      if ((ret =
          __db_shalloc(infop, nregions * sizeof(REGION), 0, &rp)) != 0) {
            __db_err(dbenv, "unable to create new master region array: %s",
                db_strerror(ret));
            goto err;
      }
      renv->region_off = R_OFFSET(infop, rp);
      for (i = 0; i < nregions; ++i, ++rp)
            rp->id = INVALID_REGION_ID;

      renv->cipher_off = INVALID_ROFF;

      renv->rep_off = INVALID_ROFF;
      renv->flags = 0;
      renv->op_timestamp = renv->rep_timestamp = 0;

      /*
       * Get the underlying REGION structure for this environment.  Note,
       * we created the underlying OS region before we acquired the REGION
       * structure, which is backwards from the normal procedure.  Update
       * the REGION structure.
       */
      if ((ret = __db_des_get(dbenv, infop, infop, &rp)) != 0) {
find_err:   __db_err(dbenv, "%s: unable to find environment", infop->name);
            if (ret == 0)
                  ret = EINVAL;
            goto err;
      }
      infop->rp = rp;
      rp->size = tregion.size;
      rp->segid = tregion.segid;

      /*
       * !!!
       * If we create an environment where regions are public and in system
       * memory, we have to inform processes joining the environment how to
       * attach to the shared memory segment.  So, we write the shared memory
       * identifier into the file, to be read by those other processes.
       *
       * XXX
       * This is really OS-layer information, but I can't see any easy way
       * to move it down there without passing down information that it has
       * no right to know, e.g., that this is the one-and-only REGENV region
       * and not some other random region.
       */
      if (tregion.segid != INVALID_REGION_SEGID) {
            ref.size = tregion.size;
            ref.segid = tregion.segid;
            if ((ret = __os_write(
                dbenv, dbenv->lockfhp, &ref, sizeof(ref), &nrw)) != 0) {
                  __db_err(dbenv,
                      "%s: unable to write out public environment ID: %s",
                      infop->name, db_strerror(ret));
                  goto err;
            }
      }

#ifndef HAVE_MUTEX_FCNTL
      /*
       * If we're not doing fcntl locking, we can close the file handle.  We
       * no longer need it and the less contact between the buffer cache and
       * the VM, the better.
       */
      if (dbenv->lockfhp != NULL) {
             (void)__os_closehandle(dbenv, dbenv->lockfhp);
             dbenv->lockfhp = NULL;
      }
#endif

      /* Everything looks good, we're done. */
      dbenv->reginfo = infop;
      return (0);

err:
retry:      /* Close any open file handle. */
      if (dbenv->lockfhp != NULL) {
            (void)__os_closehandle(dbenv, dbenv->lockfhp);
            dbenv->lockfhp = NULL;
      }

      /*
       * If we joined or created the region, detach from it.  If we created
       * it, destroy it.  Note, there's a path in the above code where we're
       * using a temporary REGION structure because we haven't yet allocated
       * the real one.  In that case the region address (addr) will be filled
       * in, but the REGION pointer (rp) won't.  Fix it.
       */
      if (infop->addr != NULL) {
            if (infop->rp == NULL)
                  infop->rp = &tregion;

            /* Reset the addr value that we "corrected" above. */
            infop->addr = infop->primary;
            (void)__os_r_detach(dbenv,
                infop, F_ISSET(infop, REGION_CREATE));
      }

      /* Free the allocated name and/or REGINFO structure. */
      if (infop->name != NULL)
            __os_free(dbenv, infop->name);
      __os_free(dbenv, infop);

      /* If we had a temporary error, wait awhile and try again. */
      if (ret == 0) {
            if (++retry_cnt > 3) {
                  __db_err(dbenv, "unable to join the environment");
                  ret = EAGAIN;
            } else {
                  __os_sleep(dbenv, retry_cnt * 3, 0);
                  goto loop;
            }
      }

      return (ret);
}

/*
 * __db_e_golive --
 *    Turn on the created environment.
 *
 * PUBLIC: int __db_e_golive __P((DB_ENV *));
 */
int
__db_e_golive(dbenv)
      DB_ENV *dbenv;
{
      REGENV *renv;
      REGINFO *infop;

      infop = dbenv->reginfo;
      renv = infop->primary;

      /* If we didn't create the region, there's no need for further work. */
      if (!F_ISSET(infop, REGION_CREATE))
            return (0);

      /*
       * Validate the file.  All other threads of control are waiting
       * on this value to be written -- "Let slip the hounds of war!"
       */
      renv->magic = DB_REGION_MAGIC;

      return (0);
}

/*
 * __db_e_detach --
 *    Detach from the environment.
 *
 * PUBLIC: int __db_e_detach __P((DB_ENV *, int));
 */
int
__db_e_detach(dbenv, destroy)
      DB_ENV *dbenv;
      int destroy;
{
      REGENV *renv;
      REGINFO *infop;
      REGION rp;
      int ret, t_ret;

      infop = dbenv->reginfo;
      renv = infop->primary;
      ret = 0;

      if (F_ISSET(dbenv, DB_ENV_PRIVATE))
            destroy = 1;

      /* Decrement the reference count. */
      MUTEX_LOCK(dbenv, renv->mtx_regenv);
      if (renv->refcnt == 0)
            __db_err(dbenv, "environment reference count went negative");
      else
            --renv->refcnt;
      MUTEX_UNLOCK(dbenv, renv->mtx_regenv);

      /* Close the locking file handle. */
      if (dbenv->lockfhp != NULL) {
            if ((t_ret =
                __os_closehandle(dbenv, dbenv->lockfhp)) != 0 && ret == 0)
                  ret = t_ret;
            dbenv->lockfhp = NULL;
      }

      /*
       * Release the region, and kill our reference.
       */
      if (destroy) {
#ifdef HAVE_CRYPTO
            /*
             * Destroy any system resources the crypto subsystem may have
             * acquired.
             */
            if ((t_ret = __crypto_region_destroy(dbenv)) != 0 && ret == 0)
                  ret = t_ret;
#endif
            /*
             * Destroy any system resources the replication subsystem may
             * have acquired.
             */
            if ((t_ret = __rep_region_destroy(dbenv)) != 0 && ret == 0)
                  ret = t_ret;

            /*
             * Free the REGION array.
             *
             * The actual underlying region structure is allocated from the
             * primary shared region, and we're about to free it.  Save a
             * copy on our stack for the REGINFO to reference when it calls
             * down into the OS layer to release the shared memory segment.
             */
            rp = *infop->rp;
            infop->rp = &rp;

            if (renv->region_off != INVALID_ROFF)
                  __db_shalloc_free(
                     infop, R_ADDR(infop, renv->region_off));

            /* Discard any mutex resources we may have acquired. */
            if ((t_ret =
                __mutex_free(dbenv, &renv->mtx_regenv)) != 0 && ret == 0)
                  ret = t_ret;
      }

      /*
       * Set the DB_ENV->reginfo field to NULL.  First, DB_ENV->remove calls
       * __env_remove to do the region remove, and __envremove attached and
       * then detaches from the region.  We don't want to return to
       * DB_ENV->remove with a non-NULL DB_ENV->reginfo field because it will
       * attempt to detach again as part of its cleanup.
       *
       * Second, DB code uses DB_ENV->reginfo to decide if it's OK to read
       * the underlying region.  We're about to destroy what it references,
       * so it needs to be cleared.
       */
      dbenv->reginfo = NULL;

      /* Reset the addr value that we "corrected" above. */
      infop->addr = infop->primary;

      if ((t_ret = __os_r_detach(dbenv, infop, destroy)) != 0 && ret == 0)
            ret = t_ret;
      if (infop->name != NULL)
            __os_free(dbenv, infop->name);

      /* Discard the DB_ENV->reginfo field's memory. */
      __os_free(dbenv, infop);

      return (ret);
}

/*
 * __db_e_remove --
 *    Discard an environment if it's not in use.
 *
 * PUBLIC: int __db_e_remove __P((DB_ENV *, u_int32_t));
 */
int
__db_e_remove(dbenv, flags)
      DB_ENV *dbenv;
      u_int32_t flags;
{
      REGENV *renv;
      REGINFO *infop, reginfo;
      REGION *rp;
      u_int32_t db_env_reset, i;
      int ret;

      db_env_reset = F_ISSET(dbenv, DB_ENV_NOLOCKING | DB_ENV_NOPANIC);

      /*
       * This routine has to walk a nasty line between not looking into
       * the environment (which may be corrupted after an app or system
       * crash), and removing everything that needs removing.  What we
       * do is:
       *    1. Connect to the environment.
       *    2. If the environment is in use (reference count is non-zero),
       *       return EBUSY.
       *    3. Panic it and overwrite the magic number so any threads of
       *       control attempting to connect (or racing with us) backoff
       *       and retry or just die.
       *    4. Walk the array of regions.  Connect to each region and then
       *       disconnect with the destroy flag set.  This shouldn't cause
       *       any problems, even if the region is corrupted, because we
       *       never look inside the region (with the single exception of
       *       mutex regions on systems where we have to return resources
       *       to the underlying system).
       *    5. Walk the list of files in the directory, unlinking any
       *       files that match a region name.  Unlink the environment
       *       file last.
       *
       * If the force flag is set, we do not acquire any locks during this
       * process.
       *
       * We're going to panic the environment, so we'll want to ignore that
       * flag.
       */
      if (LF_ISSET(DB_FORCE))
            F_SET(dbenv, DB_ENV_NOLOCKING);
      F_SET(dbenv, DB_ENV_NOPANIC);

      /* Join the environment. */
      if ((ret = __db_e_attach(dbenv, NULL)) != 0) {
            /*
             * If we can't join it, we assume that's because it doesn't
             * exist.  It would be better to know why we failed, but it
             * probably isn't important.
             */
            ret = 0;
            if (LF_ISSET(DB_FORCE))
                  goto remfiles;
            goto done;
      }

      infop = dbenv->reginfo;
      renv = infop->primary;

      /* Lock the environment. */
      MUTEX_LOCK(dbenv, renv->mtx_regenv);

      /*
       * If it's in use, we're done unless we're forcing the issue or the
       * environment has panic'd.  (Presumably, if the environment panic'd,
       * the thread holding the reference count may not have cleaned up.)
       */
      if (renv->refcnt == 1 || renv->panic == 1 || LF_ISSET(DB_FORCE)) {
            /*
             * Set the panic flag and overwrite the magic number.
             *
             * !!!
             * From this point on, there's no going back, we pretty
             * much ignore errors, and just whack on whatever we can.
             */
            renv->magic = 0;
            renv->panic = 1;

            /*
             * Unlock the environment -- nobody should need this lock
             * because we've poisoned the pool.
             */
            MUTEX_UNLOCK(dbenv, renv->mtx_regenv);

            /* Attach to each sub-region and destroy it. */
            for (rp = R_ADDR(infop, renv->region_off),
                i = 0; i < renv->region_cnt; ++i, ++rp) {
                  if (rp->id == INVALID_REGION_ID ||
                      rp->type == REGION_TYPE_ENV)
                        continue;
                  /*
                   * !!!
                   * The REGION_CREATE_OK flag is set for Windows/95 --
                   * regions are zero'd out when the last reference to
                   * the region goes away, in which case the underlying
                   * OS region code requires callers be prepared to
                   * create the region in order to join it.
                   */
                  memset(&reginfo, 0, sizeof(reginfo));
                  reginfo.id = rp->id;
                  reginfo.flags = REGION_CREATE_OK;

                  /*
                   * If we get here and can't attach and/or detach to the
                   * region, it's a mess.  Ignore errors, there's nothing
                   * we can do about them.
                   */
                  if (__db_r_attach(dbenv, &reginfo, 0) != 0)
                        continue;

#ifdef  HAVE_MUTEX_SYSTEM_RESOURCES
                  /*
                   * If destroying the mutex region, return any system
                   * resources to the system.
                   */
                  if (reginfo.type == REGION_TYPE_MUTEX)
                        __mutex_resource_return(dbenv, &reginfo);
#endif
                  (void)__db_r_detach(dbenv, &reginfo, 1);
            }

            /* Destroy the environment's region. */
            (void)__db_e_detach(dbenv, 1);

            /* Discard any remaining physical files. */
remfiles:   (void)__db_e_remfile(dbenv);
      } else {
            /* Unlock the environment. */
            MUTEX_UNLOCK(dbenv, renv->mtx_regenv);

            /* Discard the environment. */
            (void)__db_e_detach(dbenv, 0);

            ret = EBUSY;
      }

done: F_CLR(dbenv, DB_ENV_NOLOCKING | DB_ENV_NOPANIC);
      F_SET(dbenv, db_env_reset);

      return (ret);
}

/*
 * __db_e_remfile --
 *    Discard any region files in the filesystem.
 */
static int
__db_e_remfile(dbenv)
      DB_ENV *dbenv;
{
      int cnt, fcnt, lastrm, ret;
      const char *dir;
      char saved_char, *p, **names, *path, buf[sizeof(DB_REGION_FMT) + 20];

      /* Get the full path of a file in the environment. */
      (void)snprintf(buf, sizeof(buf), "%s", DB_REGION_ENV);
      if ((ret = __db_appname(dbenv, DB_APP_NONE, buf, 0, NULL, &path)) != 0)
            return (ret);

      /* Get the parent directory for the environment. */
      if ((p = __db_rpath(path)) == NULL) {
            p = path;
            saved_char = *p;

            dir = PATH_DOT;
      } else {
            saved_char = *p;
            *p = '\0';

            dir = path;
      }

      /* Get the list of file names. */
      if ((ret = __os_dirlist(dbenv, dir, &names, &fcnt)) != 0)
            __db_err(dbenv, "%s: %s", dir, db_strerror(ret));

      /* Restore the path, and free it. */
      *p = saved_char;
      __os_free(dbenv, path);

      if (ret != 0)
            return (ret);

      /*
       * Remove files from the region directory.
       */
      for (lastrm = -1, cnt = fcnt; --cnt >= 0;) {
            /* Skip anything outside our name space. */
            if (strncmp(names[cnt],
                DB_REGION_PREFIX, sizeof(DB_REGION_PREFIX) - 1))
                  continue;

            /* Skip queue extent files. */
            if (strncmp(names[cnt], "__dbq.", 6) == 0)
                  continue;

            /* Skip registry files. */
            if (strncmp(names[cnt], "__db.register", 13) == 0)
                  continue;

            /* Skip replication files. */
            if (strncmp(names[cnt], "__db.rep.", 9) == 0)
                  continue;

            /*
             * Remove the primary environment region last, because it's
             * the key to this whole mess.
             */
            if (strcmp(names[cnt], DB_REGION_ENV) == 0) {
                  lastrm = cnt;
                  continue;
            }

            /* Remove the file. */
            if (__db_appname(dbenv,
                DB_APP_NONE, names[cnt], 0, NULL, &path) == 0) {
                  /*
                   * Overwrite region files.  Temporary files would have
                   * been maintained in encrypted format, so there's no
                   * reason to overwrite them.  This is not an exact
                   * check on the file being a region file, but it's
                   * not likely to be wrong, and the worst thing that can
                   * happen is we overwrite a file that didn't need to be
                   * overwritten.
                   */
                  if (F_ISSET(dbenv, DB_ENV_OVERWRITE) &&
                      strlen(names[cnt]) == DB_REGION_NAME_LENGTH)
                        (void)__db_file_multi_write(dbenv, path);
                  (void)__os_unlink(dbenv, path);
                  __os_free(dbenv, path);
            }
      }

      if (lastrm != -1)
            if (__db_appname(dbenv,
                DB_APP_NONE, names[lastrm], 0, NULL, &path) == 0) {
                  if (F_ISSET(dbenv, DB_ENV_OVERWRITE))
                        (void)__db_file_multi_write(dbenv, path);
                  (void)__os_unlink(dbenv, path);
                  __os_free(dbenv, path);
            }
      __os_dirfree(dbenv, names, fcnt);

      return (0);
}

/*
 * __db_r_attach
 *    Join/create a region.
 *
 * PUBLIC: int __db_r_attach __P((DB_ENV *, REGINFO *, size_t));
 */
int
__db_r_attach(dbenv, infop, size)
      DB_ENV *dbenv;
      REGINFO *infop;
      size_t size;
{
      REGION *rp;
      int ret;
      char buf[sizeof(DB_REGION_FMT) + 20];

      /*
       * Find or create a REGION structure for this region.  If we create
       * it, the REGION_CREATE flag will be set in the infop structure.
       */
      F_CLR(infop, REGION_CREATE);
      if ((ret = __db_des_get(dbenv, dbenv->reginfo, infop, &rp)) != 0)
            return (ret);
      infop->dbenv = dbenv;
      infop->rp = rp;
      infop->type = rp->type;
      infop->id = rp->id;

      /*
       * __db_des_get may have created the region and reset the create
       * flag.  If we're creating the region, set the desired size.
       */
      if (F_ISSET(infop, REGION_CREATE))
            rp->size = (roff_t)size;

      /* Join/create the underlying region. */
      (void)snprintf(buf, sizeof(buf), DB_REGION_FMT, infop->id);
      if ((ret = __db_appname(dbenv,
          DB_APP_NONE, buf, 0, NULL, &infop->name)) != 0)
            goto err;
      if ((ret = __os_r_attach(dbenv, infop, rp)) != 0)
            goto err;

      /*
       * Fault the pages into memory.  Note, do this BEFORE we initialize
       * anything because we're writing pages in created regions, not just
       * reading them.
       */
      (void)__db_faultmem(dbenv,
          infop->addr, rp->size, F_ISSET(infop, REGION_CREATE));

      /*
       * !!!
       * The underlying layer may have just decided that we are going
       * to create the region.  There are various system issues that
       * can result in a useless region that requires re-initialization.
       *
       * If we created the region, initialize it for allocation.
       */
      if (F_ISSET(infop, REGION_CREATE))
            __db_shalloc_init(infop, rp->size);

      return (0);

err:  /* Discard the underlying region. */
      if (infop->addr != NULL)
            (void)__os_r_detach(dbenv,
                infop, F_ISSET(infop, REGION_CREATE));
      infop->rp = NULL;
      infop->id = INVALID_REGION_ID;

      /* Discard the REGION structure if we created it. */
      if (F_ISSET(infop, REGION_CREATE)) {
            __db_des_destroy(dbenv, rp);
            F_CLR(infop, REGION_CREATE);
      }

      return (ret);
}

/*
 * __db_r_detach --
 *    Detach from a region.
 *
 * PUBLIC: int __db_r_detach __P((DB_ENV *, REGINFO *, int));
 */
int
__db_r_detach(dbenv, infop, destroy)
      DB_ENV *dbenv;
      REGINFO *infop;
      int destroy;
{
      REGION *rp;
      int ret;

      rp = infop->rp;
      if (F_ISSET(dbenv, DB_ENV_PRIVATE))
            destroy = 1;

      /*
       * When discarding the regions as we shut down a database environment,
       * discard any allocated shared memory segments.  This is the last time
       * we use them, and db_region_destroy is the last region-specific call
       * we make.
       */
      if (F_ISSET(dbenv, DB_ENV_PRIVATE) && infop->primary != NULL)
            __db_shalloc_free(infop, infop->primary);

      /* Detach from the underlying OS region. */
      ret = __os_r_detach(dbenv, infop, destroy);

      /* If we destroyed the region, discard the REGION structure. */
      if (destroy)
            __db_des_destroy(dbenv, rp);

      /* Destroy the structure. */
      if (infop->name != NULL)
            __os_free(dbenv, infop->name);

      return (ret);
}

/*
 * __db_des_get --
 *    Return a reference to the shared information for a REGION,
 *    optionally creating a new entry.
 */
static int
__db_des_get(dbenv, env_infop, infop, rpp)
      DB_ENV *dbenv;
      REGINFO *env_infop, *infop;
      REGION **rpp;
{
      REGENV *renv;
      REGION *rp, *empty_slot, *first_type;
      u_int32_t i, maxid;

      *rpp = NULL;
      renv = env_infop->primary;

      /*
       * If the caller wants to join a region, walk through the existing
       * regions looking for a matching ID (if ID specified) or matching
       * type (if type specified).  If we return based on a matching type
       * return the "primary" region, that is, the first region that was
       * created of this type.
       *
       * Track the first empty slot and maximum region ID for new region
       * allocation.
       *
       * MaxID starts at REGION_ID_ENV, the ID of the primary environment.
       */
      maxid = REGION_ID_ENV;
      empty_slot = first_type = NULL;
      for (rp = R_ADDR(env_infop, renv->region_off),
          i = 0; i < renv->region_cnt; ++i, ++rp) {
            if (rp->id == INVALID_REGION_ID) {
                  if (empty_slot == NULL)
                        empty_slot = rp;
                  continue;
            }
            if (infop->id != INVALID_REGION_ID) {
                  if (infop->id == rp->id)
                        break;
                  continue;
            }
            if (infop->type == rp->type &&
                F_ISSET(infop, REGION_JOIN_OK) &&
                (first_type == NULL || first_type->id > rp->id))
                  first_type = rp;

            if (rp->id > maxid)
                  maxid = rp->id;
      }

      /* If we found a matching ID (or a matching type), return it. */
      if (i >= renv->region_cnt)
            rp = first_type;
      if (rp != NULL) {
            *rpp = rp;
            return (0);
      }

      /*
       * If we didn't find a region and we don't have permission to create
       * the region, fail.  The caller generates any error message.
       */
      if (!F_ISSET(infop, REGION_CREATE_OK))
            return (ENOENT);

      /*
       * If we didn't find a region and don't have room to create the region
       * fail with an error message, there's a sizing problem.
       */
      if (empty_slot == NULL) {
            __db_err(dbenv, "no room remaining for additional REGIONs");
            return (ENOENT);
      }

      /*
       * Initialize a REGION structure for the caller.  If id was set, use
       * that value, otherwise we use the next available ID.
       */
      memset(empty_slot, 0, sizeof(REGION));
      empty_slot->segid = INVALID_REGION_SEGID;

      /*
       * Set the type and ID; if no region ID was specified,
       * allocate one.
       */
      empty_slot->type = infop->type;
      empty_slot->id = infop->id == INVALID_REGION_ID ? maxid + 1 : infop->id;

      F_SET(infop, REGION_CREATE);

      *rpp = empty_slot;
      return (0);
}

/*
 * __db_des_destroy --
 *    Destroy a reference to a REGION.
 */
static void
__db_des_destroy(dbenv, rp)
      DB_ENV *dbenv;
      REGION *rp;
{
      COMPQUIET(dbenv, NULL);

      rp->id = INVALID_REGION_ID;
}

/*
 * __db_faultmem --
 *    Fault the region into memory.
 */
static int
__db_faultmem(dbenv, addr, size, created)
      DB_ENV *dbenv;
      void *addr;
      size_t size;
      int created;
{
      int ret;
      u_int8_t *p, *t;

      /* Ignore heap regions. */
      if (F_ISSET(dbenv, DB_ENV_PRIVATE))
            return (0);

      /*
       * It's sometimes significantly faster to page-fault in all of the
       * region's pages before we run the application, as we see nasty
       * side-effects when we page-fault while holding various locks, i.e.,
       * the lock takes a long time to acquire because of the underlying
       * page fault, and the other threads convoy behind the lock holder.
       *
       * If we created the region, we write a non-zero value so that the
       * system can't cheat.  If we're just joining the region, we can
       * only read the value and try to confuse the compiler sufficiently
       * that it doesn't figure out that we're never really using it.
       *
       * Touch every page (assuming pages are 512B, the smallest VM page
       * size used in any general purpose processor).
       */
      ret = 0;
      if (F_ISSET(dbenv, DB_ENV_REGION_INIT)) {
            if (created)
                  for (p = addr,
                      t = (u_int8_t *)addr + size; p < t; p += 512)
                        p[0] = 0xdb;
            else
                  for (p = addr,
                      t = (u_int8_t *)addr + size; p < t; p += 512)
                        ret |= p[0];
      }

      return (ret);
}

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