os_map.c

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996-2005
 *      Sleepycat Software.  All rights reserved.
 *
 * $Id: os_map.c,v 12.3 2005/07/21 01:36:18 bostic Exp $
 */

#include "db_config.h"

#ifndef NO_SYSTEM_INCLUDES
#include <sys/types.h>
#ifdef HAVE_MMAP
#include <sys/mman.h>
#endif

#ifdef HAVE_SHMGET
#include <sys/ipc.h>
#include <sys/shm.h>
#endif

#include <string.h>
#endif

#include "db_int.h"

#ifdef HAVE_MMAP
static int __os_map __P((DB_ENV *, char *, DB_FH *, size_t, int, int, void **));
#endif
#ifndef HAVE_SHMGET
static int __db_nosystemmem __P((DB_ENV *));
#endif

/*
 * __os_r_sysattach --
 *      Create/join a shared memory region.
 *
 * PUBLIC: int __os_r_sysattach __P((DB_ENV *, REGINFO *, REGION *));
 */
int
__os_r_sysattach(dbenv, infop, rp)
        DB_ENV *dbenv;
        REGINFO *infop;
        REGION *rp;
{
        if (F_ISSET(dbenv, DB_ENV_SYSTEM_MEM)) {
                /*
                 * If the region is in system memory on UNIX, we use shmget(2).
                 *
                 * !!!
                 * There exist spinlocks that don't work in shmget memory, e.g.,
                 * the HP/UX msemaphore interface.  If we don't have locks that
                 * will work in shmget memory, we better be private and not be
                 * threaded.  If we reach this point, we know we're public, so
                 * it's an error.
                 */
#if defined(HAVE_MUTEX_HPPA_MSEM_INIT)
                __db_err(dbenv,
            "architecture does not support locks inside system shared memory");
                return (EINVAL);
#endif
#if defined(HAVE_SHMGET)
                {
                key_t segid;
                int id, mode, ret;

                /*
                 * We could potentially create based on REGION_CREATE_OK, but
                 * that's dangerous -- we might get crammed in sideways if
                 * some of the expected regions exist but others do not.  Also,
                 * if the requested size differs from an existing region's
                 * actual size, then all sorts of nasty things can happen.
                 * Basing create solely on REGION_CREATE is much safer -- a
                 * recovery will get us straightened out.
                 */
                if (F_ISSET(infop, REGION_CREATE)) {
                        /*
                         * The application must give us a base System V IPC key
                         * value.  Adjust that value based on the region's ID,
                         * and correct so the user's original value appears in
                         * the ipcs output.
                         */
                        if (dbenv->shm_key == INVALID_REGION_SEGID) {
                                __db_err(dbenv,
                            "no base system shared memory ID specified");
                                return (EINVAL);
                        }
                        segid = (key_t)(dbenv->shm_key + (infop->id - 1));

                        /*
                         * If map to an existing region, assume the application
                         * crashed and we're restarting.  Delete the old region
                         * and re-try.  If that fails, return an error, the
                         * application will have to select a different segment
                         * ID or clean up some other way.
                         */
                        if ((id = shmget(segid, 0, 0)) != -1) {
                                (void)shmctl(id, IPC_RMID, NULL);
                                if ((id = shmget(segid, 0, 0)) != -1) {
                                        __db_err(dbenv,
                "shmget: key: %ld: shared system memory region already exists",
                                            (long)segid);
                                        return (EAGAIN);
                                }
                        }

                        /*
                         * Map the DbEnv::open method file mode permissions to
                         * shmget call permissions.
                         */
                        mode = IPC_CREAT | __db_shm_mode(dbenv);
                        if ((id = shmget(segid, rp->size, mode)) == -1) {
                                ret = __os_get_errno();
                                __db_err(dbenv,
        "shmget: key: %ld: unable to create shared system memory region: %s",
                                    (long)segid, strerror(ret));
                                return (ret);
                        }
                        rp->segid = id;
                } else
                        id = rp->segid;

                if ((infop->addr = shmat(id, NULL, 0)) == (void *)-1) {
                        infop->addr = NULL;
                        ret = __os_get_errno();
                        __db_err(dbenv,
        "shmat: id %d: unable to attach to shared system memory region: %s",
                            id, strerror(ret));
                        return (ret);
                }

                return (0);
                }
#else
                return (__db_nosystemmem(dbenv));
#endif
        }

#ifdef HAVE_MMAP
        {
        DB_FH *fhp;
        int ret;

        fhp = NULL;

        /*
         * Try to open/create the shared region file.  We DO NOT need to ensure
         * that multiple threads/processes attempting to simultaneously create
         * the region are properly ordered, our caller has already taken care
         * of that.
         */
        if ((ret = __os_open(dbenv, infop->name,
            DB_OSO_REGION |
            (F_ISSET(infop, REGION_CREATE_OK) ? DB_OSO_CREATE : 0),
            dbenv->db_mode, &fhp)) != 0)
                __db_err(dbenv, "%s: %s", infop->name, db_strerror(ret));

        /*
         * If we created the file, grow it to its full size before mapping
         * it in.  We really want to avoid touching the buffer cache after
         * mmap(2) is called, doing anything else confuses the hell out of
         * systems without merged VM/buffer cache systems, or, more to the
         * point, *badly* merged VM/buffer cache systems.
         */
        if (ret == 0 && F_ISSET(infop, REGION_CREATE)) {
                if (F_ISSET(dbenv, DB_ENV_REGION_INIT))
                        ret = __db_file_write(dbenv, "region file", fhp,
                            rp->size / MEGABYTE, rp->size % MEGABYTE, 0x00);
                else
                        ret = __db_file_extend(dbenv, fhp, rp->size);
        }

        /* Map the file in. */
        if (ret == 0)
                ret = __os_map(dbenv,
                    infop->name, fhp, rp->size, 1, 0, &infop->addr);

        if (fhp != NULL)
                (void)__os_closehandle(dbenv, fhp);

        return (ret);
        }
#else
        COMPQUIET(infop, NULL);
        COMPQUIET(rp, NULL);
        __db_err(dbenv,
            "architecture lacks mmap(2), shared environments not possible");
        return (DB_OPNOTSUP);
#endif
}

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

        rp = infop->rp;

        if (F_ISSET(dbenv, DB_ENV_SYSTEM_MEM)) {
#ifdef HAVE_SHMGET
                int ret, segid;

                /*
                 * We may be about to remove the memory referenced by rp,
                 * save the segment ID, and (optionally) wipe the original.
                 */
                segid = rp->segid;
                if (destroy)
                        rp->segid = INVALID_REGION_SEGID;

                if (shmdt(infop->addr) != 0) {
                        ret = __os_get_errno();
                        __db_err(dbenv, "shmdt: %s", strerror(ret));
                        return (ret);
                }

                if (destroy && shmctl(segid, IPC_RMID,
                    NULL) != 0 && (ret = __os_get_errno()) != EINVAL) {
                        __db_err(dbenv,
            "shmctl: id %d: unable to delete system shared memory region: %s",
                            segid, strerror(ret));
                        return (ret);
                }

                return (0);
#else
                return (__db_nosystemmem(dbenv));
#endif
        }

#ifdef HAVE_MMAP
#ifdef HAVE_MUNLOCK
        if (F_ISSET(dbenv, DB_ENV_LOCKDOWN))
                (void)munlock(infop->addr, rp->size);
#endif
        if (munmap(infop->addr, rp->size) != 0) {
                int ret;

                ret = __os_get_errno();
                __db_err(dbenv, "munmap: %s", strerror(ret));
                return (ret);
        }

        if (destroy && __os_region_unlink(dbenv, infop->name) != 0)
                return (__os_get_errno());

        return (0);
#else
        COMPQUIET(destroy, 0);
        return (EINVAL);
#endif
}

/*
 * __os_mapfile --
 *      Map in a shared memory file.
 *
 * PUBLIC: int __os_mapfile __P((DB_ENV *,
 * PUBLIC:     char *, DB_FH *, size_t, int, void **));
 */
int
__os_mapfile(dbenv, path, fhp, len, is_rdonly, addrp)
        DB_ENV *dbenv;
        char *path;
        DB_FH *fhp;
        int is_rdonly;
        size_t len;
        void **addrp;
{
#if defined(HAVE_MMAP) && !defined(HAVE_QNX)
        return (__os_map(dbenv, path, fhp, len, 0, is_rdonly, addrp));
#else
        COMPQUIET(dbenv, NULL);
        COMPQUIET(path, NULL);
        COMPQUIET(fhp, NULL);
        COMPQUIET(is_rdonly, 0);
        COMPQUIET(len, 0);
        COMPQUIET(addrp, NULL);
        return (EINVAL);
#endif
}

/*
 * __os_unmapfile --
 *      Unmap the shared memory file.
 *
 * PUBLIC: int __os_unmapfile __P((DB_ENV *, void *, size_t));
 */
int
__os_unmapfile(dbenv, addr, len)
        DB_ENV *dbenv;
        void *addr;
        size_t len;
{
        int ret;

        /* If the user replaced the map call, call through their interface. */
        if (DB_GLOBAL(j_unmap) != NULL)
                return (DB_GLOBAL(j_unmap)(addr, len));

#ifdef HAVE_MMAP
#ifdef HAVE_MUNLOCK
        if (F_ISSET(dbenv, DB_ENV_LOCKDOWN))
                RETRY_CHK((munlock(addr, len)), ret);
#else
        COMPQUIET(dbenv, NULL);
#endif
        RETRY_CHK((munmap(addr, len)), ret);
        return (ret);
#else
        COMPQUIET(dbenv, NULL);

        return (EINVAL);
#endif
}

#ifdef HAVE_MMAP
/*
 * __os_map --
 *      Call the mmap(2) function.
 */
static int
__os_map(dbenv, path, fhp, len, is_region, is_rdonly, addrp)
        DB_ENV *dbenv;
        char *path;
        DB_FH *fhp;
        int is_region, is_rdonly;
        size_t len;
        void **addrp;
{
        void *p;
        int flags, prot, ret;

        /* If the user replaced the map call, call through their interface. */
        if (DB_GLOBAL(j_map) != NULL)
                return (DB_GLOBAL(j_map)
                    (path, len, is_region, is_rdonly, addrp));

        /* Check for illegal usage. */
        DB_ASSERT(F_ISSET(fhp, DB_FH_OPENED) && fhp->fd != -1);

        /*
         * If it's read-only, it's private, and if it's not, it's shared.
         * Don't bother with an additional parameter.
         */
        flags = is_rdonly ? MAP_PRIVATE : MAP_SHARED;

#ifdef MAP_FILE
        /*
         * Historically, MAP_FILE was required for mapping regular files,
         * even though it was the default.  Some systems have it, some
         * don't, some that have it set it to 0.
         */
        flags |= MAP_FILE;
#endif

        /*
         * I know of no systems that implement the flag to tell the system
         * that the region contains semaphores, but it's not an unreasonable
         * thing to do, and has been part of the design since forever.  I
         * don't think anyone will object, but don't set it for read-only
         * files, it doesn't make sense.
         */
#ifdef MAP_HASSEMAPHORE
        if (is_region && !is_rdonly)
                flags |= MAP_HASSEMAPHORE;
#else
        COMPQUIET(is_region, 0);
#endif

        /*
         * FreeBSD:
         * Causes data dirtied via this VM map to be flushed to physical media
         * only when necessary (usually by the pager) rather then gratuitously.
         * Typically this prevents the update daemons from flushing pages
         * dirtied through such maps and thus allows efficient sharing of
         * memory across unassociated processes using a file-backed shared
         * memory map.
         */
#ifdef MAP_NOSYNC
        flags |= MAP_NOSYNC;
#endif

        prot = PROT_READ | (is_rdonly ? 0 : PROT_WRITE);

        /*
         * XXX
         * Work around a bug in the VMS V7.1 mmap() implementation.  To map
         * a file into memory on VMS it needs to be opened in a certain way,
         * originally.  To get the file opened in that certain way, the VMS
         * mmap() closes the file and re-opens it.  When it does this, it
         * doesn't flush any caches out to disk before closing.  The problem
         * this causes us is that when the memory cache doesn't get written
         * out, the file isn't big enough to match the memory chunk and the
         * mmap() call fails.  This call to fsync() fixes the problem.  DEC
         * thinks this isn't a bug because of language in XPG5 discussing user
         * responsibility for on-disk and in-memory synchronization.
         */
#ifdef VMS
        if (__os_fsync(dbenv, fhp) == -1)
                return (__os_get_errno());
#endif

        /* MAP_FAILED was not defined in early mmap implementations. */
#ifndef MAP_FAILED
#define MAP_FAILED      -1
#endif
        if ((p = mmap(NULL,
            len, prot, flags, fhp->fd, (off_t)0)) == (void *)MAP_FAILED) {
                ret = __os_get_errno();
                __db_err(dbenv, "mmap: %s", strerror(ret));
                return (ret);
        }

#ifdef HAVE_MLOCK
        /*
         * If it's a region, we want to make sure that the memory isn't paged.
         * For example, Solaris will page large mpools because it thinks that
         * I/O buffer memory is more important than we are.  The mlock system
         * call may or may not succeed (mlock is restricted to the super-user
         * on some systems).  Currently, the only other use of mmap in DB is
         * to map read-only databases -- we don't want them paged, either, so
         * the call isn't conditional.
         */
        if (F_ISSET(dbenv, DB_ENV_LOCKDOWN) && mlock(p, len) != 0) {
                ret = __os_get_errno();
                (void)munmap(p, len);
                __db_err(dbenv, "mlock: %s", strerror(ret));
                return (ret);
        }
#else
        COMPQUIET(dbenv, NULL);
#endif

        *addrp = p;
        return (0);
}
#endif

#ifndef HAVE_SHMGET
/*
 * __db_nosystemmem --
 *      No system memory environments error message.
 */
static int
__db_nosystemmem(dbenv)
        DB_ENV *dbenv;
{
        __db_err(dbenv,
            "architecture doesn't support environments in system memory");
        return (DB_OPNOTSUP);
}
#endif

---