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env_region.c

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996-2003
 *    Sleepycat Software.  All rights reserved.
 */

#include "db_config.h"

#ifndef lint
static const char revid[] = "$Id: env_region.c,v 11.79 2003/10/31 01:56:10 bostic Exp $";
#endif /* not lint */

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

#include <string.h>
#endif

#include "db_int.h"
#include "dbinc/db_shash.h"
#include "dbinc/lock.h"
#include "dbinc/log.h"
#include "dbinc/mp.h"
#include "dbinc/txn.h"

static int  __db_des_destroy __P((DB_ENV *, REGION *, int));
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));
static void __db_region_destroy __P((DB_ENV *, REGINFO *));

/*
 * __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 mbytes, bytes;
      int retry_cnt, ret, segid;
      char buf[sizeof(DB_REGION_FMT) + 20];

#if !defined(HAVE_MUTEX_THREADS)
      /*
       * !!!
       * If we don't have spinlocks, we need a file descriptor for fcntl(2)
       * locking.  We use the file handle from the REGENV file for this
       * purpose.
       *
       * Since we may be using shared memory regions, e.g., shmget(2), and
       * not a mapped-in regular file, the backing file may be only a few
       * bytes in length.  So, this depends on the ability to call fcntl to
       * lock file offsets much larger than the actual physical file.  I
       * think that's safe -- besides, very few systems actually need this
       * kind of support, SunOS is the only one still in wide use of which
       * I'm aware.
       *
       * The error case is if an application lacks spinlocks and wants to be
       * threaded.  That doesn't work because fcntl may lock the underlying
       * process, including all its threads.
       */
      if (F_ISSET(dbenv, DB_ENV_THREAD)) {
            __db_err(dbenv,
"architecture lacks fast mutexes: applications cannot be threaded");
            return (EINVAL);
      }
#endif

      /* 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->type = REGION_TYPE_ENV;
      infop->id = REGION_ID_ENV;
      infop->mode = dbenv->db_mode;
      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 do locking using locks in the region, 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_DIRECT | 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 | DB_OSO_DIRECT,
          dbenv->db_mode, &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.  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;

      /*
       * If not doing thread locking, we need to save the file handle for
       * fcntl(2) locking.  Otherwise, discard the handle, we no longer
       * need it, and the less contact between the buffer cache and the VM,
       * the better.
       */
#ifdef HAVE_MUTEX_THREADS
       (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 = R_ADDR(infop, 0);
      infop->addr = (u_int8_t *)infop->addr + sizeof(REGENV);
      renv = infop->primary;

      /* Make sure the region matches our build. */
      if (renv->majver != DB_VERSION_MAJOR ||
          renv->minver != DB_VERSION_MINOR) {
            __db_err(dbenv,
      "Program version %d.%d doesn't match environment version",
                DB_VERSION_MAJOR, DB_VERSION_MINOR);
#ifndef DIAGNOSTIC
            ret = EINVAL;
            goto err;
#endif
      }

      /*
       * 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->envpanic && !F_ISSET(dbenv, DB_ENV_NOPANIC)) {
            ret = __db_panic_msg(dbenv);
            goto err;
      }
      if (renv->magic != DB_REGION_MAGIC)
            goto retry;

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

      /*
       * Finally!  We own the environment now.  Repeat the panic check, it's
       * possible that it was set while we waited for the lock.
       */
      if (renv->envpanic && !F_ISSET(dbenv, DB_ENV_NOPANIC)) {
            ret = __db_panic_msg(dbenv);
            goto err_unlock;
      }

      /*
       * Get a reference to the underlying REGION information for this
       * environment.
       */
      if ((ret = __db_des_get(dbenv, infop, infop, &rp)) != 0 || rp == NULL) {
            MUTEX_UNLOCK(dbenv, &renv->mutex);
            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 releasing the environment for us to lock.)
       */
      if (rp->size != size) {
err_unlock: MUTEX_UNLOCK(dbenv, &renv->mutex);
            goto retry;
      }

      /* Increment the reference count. */
      ++renv->refcnt;

      /*
       * If our caller wants them, return the flags this environment was
       * initialized with.
       */
      if (init_flagsp != NULL)
            *init_flagsp = renv->init_flags;

      /* Discard our lock. */
      MUTEX_UNLOCK(dbenv, &renv->mutex);

      /*
       * 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 50 REGION structures plus overhead (we're going
       * to use this space for last-ditch allocation requests), although we
       * should never need anything close to that.
       *
       * Encryption passwds are stored in the env region.  Add that in too.
       */
      memset(&tregion, 0, sizeof(tregion));
      tregion.size = (roff_t)(50 * sizeof(REGION) +
          dbenv->passwd_len + 2048);
      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 = R_ADDR(infop, 0);
      infop->addr = (u_int8_t *)infop->addr + sizeof(REGENV);
      __db_shalloc_init(infop->addr, tregion.size - sizeof(REGENV));

      /*
       * Initialize the rest of the REGENV structure, except for the magic
       * number which validates the file/environment.
       */
      renv = infop->primary;
      renv->envpanic = 0;
      db_version(&renv->majver, &renv->minver, &renv->patch);
      SH_LIST_INIT(&renv->regionq);
      renv->refcnt = 1;
      renv->cipher_off = INVALID_ROFF;
      renv->rep_off = INVALID_ROFF;

      /*
       * 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;

      /*
       * Lock the environment.
       *
       * Check the lock call return.  This is the first lock we initialize
       * and acquire, and we have to know if it fails.  (It CAN fail, e.g.,
       * SunOS, when using fcntl(2) for locking and using an in-memory
       * filesystem as the database home.  But you knew that, I'm sure -- it
       * probably wasn't even worth mentioning.)
       */
      if ((ret = __db_mutex_setup(dbenv, infop, &renv->mutex,
          MUTEX_NO_RECORD | MUTEX_NO_RLOCK)) != 0) {
            __db_err(dbenv, "%s: unable to initialize environment lock: %s",
                infop->name, db_strerror(ret));
            goto err;
      }

      if (!F_ISSET(&renv->mutex, MUTEX_IGNORE) &&
          (ret = __db_mutex_lock(dbenv, &renv->mutex)) != 0) {
            __db_err(dbenv, "%s: unable to acquire environment lock: %s",
                infop->name, db_strerror(ret));
            goto err;
      }

      /*
       * 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;
            }
      }

      /*
       * If not doing thread locking, we need to save the file handle for
       * fcntl(2) locking.  Otherwise, discard the handle, we no longer
       * need it, and the less contact between the buffer cache and the VM,
       * the better.
       */
#if defined(HAVE_MUTEX_THREADS)
      if (dbenv->lockfhp != NULL) {
             (void)__os_closehandle(dbenv, dbenv->lockfhp);
             dbenv->lockfhp = NULL;
      }
#endif

      /* Validate the file. */
      renv->magic = DB_REGION_MAGIC;

      /* Discard our lock. */
      MUTEX_UNLOCK(dbenv, &renv->mutex);

      /* 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 {
                  (void)__os_sleep(dbenv, retry_cnt * 3, 0);
                  goto loop;
            }
      }

      return (ret);
}

/*
 * __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;

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

      if (F_ISSET(dbenv, DB_ENV_PRIVATE))
            destroy = 1;
      /* Lock the environment. */
      MUTEX_LOCK(dbenv, &renv->mutex);

      /* Decrement the reference count. */
      if (renv->refcnt == 0) {
            __db_err(dbenv,
                "region %lu (environment): reference count went negative",
                (u_long)infop->rp->id);
      } else
            --renv->refcnt;

      /* Release the lock. */
      MUTEX_UNLOCK(dbenv, &renv->mutex);

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

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

      /*
       * If we are destroying the environment, we need to
       * destroy any system resources backing the mutex, as well
       * as any system resources that the replication system may have
       * acquired and put in the main region.
       *
       * Do these now before we free the memory in __os_r_detach.
       */
      if (destroy) {
            (void)__rep_region_destroy(dbenv);
            __db_mutex_destroy(&renv->mutex);
            __db_mutex_destroy(&infop->rp->mutex);
      }

      /*
       * Release the region, and kill our reference.
       *
       * We set the DB_ENV->reginfo field to NULL here and discard its memory.
       * DB_ENV->remove calls __dbenv_remove to do the region remove, and
       * __dbenv_remove 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.
       */
      (void)__os_r_detach(dbenv, infop, destroy);

      if (infop->name != NULL)
            __os_free(dbenv, infop->name);
      __os_free(dbenv, dbenv->reginfo);
      dbenv->reginfo = NULL;

      return (0);
}

/*
 * __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;
      int force, ret;

      force = LF_ISSET(DB_FORCE) ? 1 : 0;
      /*
       * 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 (so it better be OK).
       *    2. If the environment is in use (reference count is non-zero),
       *       return EBUSY.
       *    3. Overwrite the magic number so that any threads of control
       *       attempting to connect will backoff and retry.
       *    4. Walk the list 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
       *       should never be looking inside the region.
       *    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.
       */
      db_env_reset = F_ISSET(dbenv, DB_ENV_NOLOCKING | DB_ENV_NOPANIC);
      if (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 (force)
                  goto remfiles;
            goto done;
      }

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

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

      /*
       * 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->envpanic == 1 || 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->envpanic = 1;
            renv->magic = 0;

            /*
             * Unlock the environment.  We should no longer need the lock
             * because we've poisoned the pool, but we can't continue to
             * hold it either, because other routines may want it.
             */
            MUTEX_UNLOCK(dbenv, &renv->mutex);

            /*
             * Attach to each sub-region and destroy it.
             *
             * !!!
             * 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));
            for (rp = SH_LIST_FIRST(&renv->regionq, __db_region);
                rp != NULL; rp = SH_LIST_NEXT(rp, q, __db_region)) {
                  if (rp->type == REGION_TYPE_ENV)
                        continue;

                  /*
                   * 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.
                   */
                  reginfo.id = rp->id;
                  reginfo.flags = REGION_CREATE_OK;
                  if (__db_r_attach(dbenv, &reginfo, 0) == 0) {
                        R_UNLOCK(dbenv, &reginfo);
                        (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->mutex);

            /* 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;
      u_int8_t saved_byte;
      const char *dir;
      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_byte = *p;

            dir = PATH_DOT;
      } else {
            saved_byte = *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_byte;
      __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;

            /*
             * 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_overwrite(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_overwrite(dbenv, path);
                  (void)__os_unlink(dbenv, path);
                  __os_free(dbenv, path);
            }
      __os_dirfree(dbenv, names, fcnt);

      return (0);
}

/*
 * __db_e_stat
 *    Statistics for the environment.
 *
 * PUBLIC: int __db_e_stat __P((DB_ENV *,
 * PUBLIC:       REGENV *, REGION *, int *, u_int32_t));
 */
int
__db_e_stat(dbenv, arg_renv, arg_regions, arg_regions_cnt, flags)
      DB_ENV *dbenv;
      REGENV *arg_renv;
      REGION *arg_regions;
      int *arg_regions_cnt;
      u_int32_t flags;
{
      REGENV *renv;
      REGINFO *infop;
      REGION *rp;
      int n, ret;

      infop = dbenv->reginfo;
      renv = infop->primary;
      rp = infop->rp;
      if ((ret = __db_fchk(dbenv,
          "DB_ENV->stat", flags, DB_STAT_CLEAR)) != 0)
            return (ret);

      /* Lock the environment. */
      MUTEX_LOCK(dbenv, &rp->mutex);

      *arg_renv = *renv;
      if (LF_ISSET(DB_STAT_CLEAR)) {
            renv->mutex.mutex_set_nowait = 0;
            renv->mutex.mutex_set_wait = 0;
      }

      for (n = 0, rp = SH_LIST_FIRST(&renv->regionq, __db_region);
          n < *arg_regions_cnt && rp != NULL;
          ++n, rp = SH_LIST_NEXT(rp, q, __db_region)) {
            arg_regions[n] = *rp;
            if (LF_ISSET(DB_STAT_CLEAR)) {
                  rp->mutex.mutex_set_nowait = 0;
                  rp->mutex.mutex_set_wait = 0;
            }
      }

      /* Release the lock. */
      rp = infop->rp;
      MUTEX_UNLOCK(dbenv, &rp->mutex);

      *arg_regions_cnt = n == 0 ? n : n - 1;

      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;
{
      REGENV *renv;
      REGION *rp;
      int ret;
      char buf[sizeof(DB_REGION_FMT) + 20];

      renv = ((REGINFO *)dbenv->reginfo)->primary;

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

      /*
       * 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) {
            MUTEX_UNLOCK(dbenv, &renv->mutex);
            return (ret);
      }
      infop->rp = rp;
      infop->type = rp->type;
      infop->id = rp->id;

      /* 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))
            (void)__db_shalloc_init(infop->addr, rp->size);

      /*
       * If the underlying REGION isn't the environment, acquire a lock
       * for it and release our lock on the environment.
       */
      if (infop->type != REGION_TYPE_ENV) {
            MUTEX_LOCK(dbenv, &rp->mutex);
            MUTEX_UNLOCK(dbenv, &renv->mutex);
      }

      return (0);

      /* Discard the underlying region. */
err:  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)) {
            (void)__db_des_destroy(dbenv, rp, 1);
            F_CLR(infop, REGION_CREATE);
      }

      /* Release the environment lock. */
      MUTEX_UNLOCK(dbenv, &renv->mutex);

      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;
{
      REGENV *renv;
      REGION *rp;
      int ret, t_ret;

      renv = ((REGINFO *)dbenv->reginfo)->primary;
      rp = infop->rp;
      if (F_ISSET(dbenv, DB_ENV_PRIVATE))
            destroy = 1;

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

      /* Acquire the lock for the REGION. */
      MUTEX_LOCK(dbenv, &rp->mutex);

      /*
       * We need to call destroy on per-subsystem info before
       * we free the memory associated with the region.
       */
      if (destroy)
            __db_region_destroy(dbenv, infop);

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

      /* Release the REGION lock. */
      MUTEX_UNLOCK(dbenv, &rp->mutex);

      /*
       * If we destroyed the region, discard the REGION structure.  The only
       * time this routine is called with the destroy flag set is when the
       * environment is being removed, and it's likely that the only reason
       * the environment is being removed is because we crashed.  Don't do
       * any unnecessary shared memory manipulation.
       */
      if (destroy &&
          ((t_ret = __db_des_destroy(dbenv, rp, 0)) != 0) && ret == 0)
            ret = t_ret;

      /* Release the environment lock. */
      MUTEX_UNLOCK(dbenv, &renv->mutex);

      /* 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, *first_type;
      u_int32_t maxid;
      int ret;

      /*
       * !!!
       * Called with the environment already locked.
       */
      *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 maximum region ID so we can allocate a new region,
       * note that we have to start at 1 because the primary environment
       * uses ID == 1.
       */
      maxid = REGION_ID_ENV;
      for (first_type = NULL,
          rp = SH_LIST_FIRST(&renv->regionq, __db_region);
          rp != NULL; rp = SH_LIST_NEXT(rp, q, __db_region)) {
            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 (rp == NULL)
            rp = first_type;

      /*
       * If we didn't find a region and we can't create the region, fail.
       * The caller generates any error message.
       */
      if (rp == NULL && !F_ISSET(infop, REGION_CREATE_OK))
            return (ENOENT);

      /*
       * If we didn't find a region, create and initialize a REGION structure
       * for the caller.  If id was set, use that value, otherwise we use the
       * next available ID.
       */
      if (rp == NULL) {
            if ((ret = __db_shalloc(env_infop->addr,
                sizeof(REGION), MUTEX_ALIGN, &rp)) != 0)
                  return (ret);

            /* Initialize the region. */
            memset(rp, 0, sizeof(*rp));
            if ((ret = __db_mutex_setup(dbenv, env_infop, &rp->mutex,
                MUTEX_NO_RECORD | MUTEX_NO_RLOCK)) != 0) {
                  __db_shalloc_free(env_infop->addr, rp);
                  return (ret);
            }
            rp->segid = INVALID_REGION_SEGID;

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

            SH_LIST_INSERT_HEAD(&renv->regionq, rp, q, __db_region);
            F_SET(infop, REGION_CREATE);
      }

      *rpp = rp;
      return (0);
}

/*
 * __db_des_destroy --
 *    Destroy a reference to a REGION.
 */
static int
__db_des_destroy(dbenv, rp, shmem_safe)
      DB_ENV *dbenv;
      REGION *rp;
      int shmem_safe;
{
      REGINFO *infop;

      /*
       * !!!
       * Called with the environment already locked.
       */
      infop = dbenv->reginfo;

      /*
       * If we're calling during recovery, it may not be safe to access the
       * shared memory, as the shared memory may have been corrupted during
       * the crash.  If the shared memory is safe, remove the REGION entry
       * from its linked list, destroy the mutex, and free the allocated
       * memory.  On systems that require system mutex support, we don't
       * have a choice -- safe or not, we have to destroy the mutex or we'll
       * leak memory.
       */
      if (shmem_safe)
            SH_LIST_REMOVE(rp, q, __db_region);

      __db_mutex_destroy(&rp->mutex);

      if (shmem_safe)
            __db_shalloc_free(infop->addr, rp);

      return (0);
}

/*
 * __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;

      /*
       * 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.
       */
      ret = 0;
      if (F_ISSET(dbenv, DB_ENV_REGION_INIT)) {
            if (created)
                  for (p = addr, t = (u_int8_t *)addr + size;
                      p < t; p += OS_VMPAGESIZE)
                        p[0] = 0xdb;
            else
                  for (p = addr, t = (u_int8_t *)addr + size;
                      p < t; p += OS_VMPAGESIZE)
                        ret |= p[0];
      }

      return (ret);
}

/*
 * __db_region_destroy --
 *    Destroy per-subsystem region information.
 *    Called with the region already locked.
 */
static void
__db_region_destroy(dbenv, infop)
      DB_ENV *dbenv;
      REGINFO *infop;
{
      switch (infop->type) {
      case REGION_TYPE_LOCK:
            __lock_region_destroy(dbenv, infop);
            break;
      case REGION_TYPE_LOG:
            __log_region_destroy(dbenv, infop);
            break;
      case REGION_TYPE_MPOOL:
            __mpool_region_destroy(dbenv, infop);
            break;
      case REGION_TYPE_TXN:
            __txn_region_destroy(dbenv, infop);
            break;
      case REGION_TYPE_ENV:
      case REGION_TYPE_MUTEX:
            break;
      default:
            DB_ASSERT(0);
            break;
      }
}

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