db/os/os_map.c

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996, 1997, 1998
 *  Sleepycat Software.  All rights reserved.
 */

#include "config.h"

#ifndef lint
static const char sccsid[] = "@(#)os_map.c  10.24 (Sleepycat) 10/12/98";
#endif /* not lint */

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

#include "db_int.h"
#include "os_jump.h"
#include "common_ext.h"

#ifdef HAVE_MMAP
static int __os_map __P((char *, int, size_t, int, int, int, void **));
#endif
#ifdef HAVE_SHMGET
static int __os_shmget __P((REGINFO *));
#endif

/*
 * __db_mapanon_ok --
 *  Return if this OS can support anonymous memory regions.
 *
 * PUBLIC: int __db_mapanon_ok __P((int));
 */
int
__db_mapanon_ok(need_names)
    int need_names;
{
    int ret;

    ret = EINVAL;

    /*
     * If we don't have spinlocks, we have to have a file descriptor
     * for fcntl(2) locking, which implies using mmap(2) to map in a
     * regular file.  Theoretically, we could probably find ways to
     * get a file descriptor to lock other types of shared regions,
     * but I don't see any reason to do so.
     *
     * If need_names is set, the application wants to share anonymous
     * memory among multiple processes, so we have to have a way to
     * name it.  This requires shmget(2), on UNIX systems.
     */
#ifdef HAVE_SPINLOCKS
#ifdef HAVE_SHMGET
    ret = 0;
#endif
#ifdef HAVE_MMAP
#ifdef MAP_ANON
    if (!need_names)
        ret = 0;
#endif
#ifdef MAP_ANONYMOUS
    if (!need_names)
        ret = 0;
#endif
#else
    COMPQUIET(need_names, 0);
#endif /* HAVE_MMAP */
#endif /* HAVE_SPINLOCKS */

    return (ret);
}

/*
 * __db_mapinit --
 *  Return if shared regions need to be initialized.
 *
 * PUBLIC: int __db_mapinit __P((void));
 */
int
__db_mapinit()
{
    /*
     * Historically, some systems required that all of the bytes of the
     * region be written before it could be mmapped and accessed randomly.
     * We have the option of setting REGION_INIT_NEEDED at configuration
     * time if we're running on one of those systems.
     */
#ifdef REGION_INIT_NEEDED
    return (1);
#else
    return (0);
#endif
}

/*
 * __db_mapregion --
 *  Attach to a shared memory region.
 *
 * PUBLIC: int __db_mapregion __P((char *, REGINFO *));
 */
int
__db_mapregion(path, infop)
    char *path;
    REGINFO *infop;
{
    int called, ret;

    called = 0;
    ret = EINVAL;

    /* If the user replaces the map call, call through their interface. */
    if (__db_jump.j_map != NULL) {
        F_SET(infop, REGION_HOLDINGSYS);
        return (__db_jump.j_map(path, infop->fd, infop->size,
            1, F_ISSET(infop, REGION_ANONYMOUS), 0, &infop->addr));
    }

    if (F_ISSET(infop, REGION_ANONYMOUS)) {
        /*
         * !!!
         * If we're creating anonymous regions:
         *
         * If it's private, we use mmap(2).  The problem with using
         * shmget(2) is that we may be creating a region of which the
         * application isn't aware, and if the application crashes
         * we'll have no way to remove the system resources for the
         * region.
         *
         * If it's not private, we use the shmget(2) interface if it's
         * available, because it allows us to name anonymous memory.
         * If shmget(2) isn't available, use the mmap(2) calls.
         *
         * In the case of anonymous memory, using mmap(2) means the
         * memory isn't named and only the single process and its
         * threads can access the region.
         */
#ifdef  HAVE_MMAP
#ifdef  MAP_ANON
#define HAVE_MMAP_ANONYMOUS 1
#else
#ifdef  MAP_ANONYMOUS
#define HAVE_MMAP_ANONYMOUS 1
#endif
#endif
#endif
#ifdef HAVE_MMAP_ANONYMOUS
        if (!called && F_ISSET(infop, REGION_PRIVATE)) {
            called = 1;
            ret = __os_map(path,
                infop->fd, infop->size, 1, 1, 0, &infop->addr);
        }
#endif
#ifdef HAVE_SHMGET
        if (!called) {
            called = 1;
            ret = __os_shmget(infop);
        }
#endif
#ifdef HAVE_MMAP
        /*
         * If we're trying to join an unnamed anonymous region, fail --
         * that's not possible.
         */
        if (!called) {
            called = 1;

            if (!F_ISSET(infop, REGION_CREATED)) {
                __db_err(infop->dbenv,
                "cannot join region in unnamed anonymous memory");
                return (EINVAL);
            }

            ret = __os_map(path,
                infop->fd, infop->size, 1, 1, 0, &infop->addr);
        }
#endif
    } else {
        /*
         * !!!
         * If we're creating normal regions, we use the mmap(2)
         * interface if it's available because it's POSIX 1003.1
         * standard and we trust it more than we do shmget(2).
         */
#ifdef HAVE_MMAP
        if (!called) {
            called = 1;

            /* Mmap(2) regions that aren't anonymous can grow. */
            F_SET(infop, REGION_CANGROW);

            ret = __os_map(path,
                infop->fd, infop->size, 1, 0, 0, &infop->addr);
        }
#endif
#ifdef HAVE_SHMGET
        if (!called) {
            called = 1;
            ret = __os_shmget(infop);
        }
#endif
    }
    return (ret);
}

/*
 * __db_unmapregion --
 *  Detach from the shared memory region.
 *
 * PUBLIC: int __db_unmapregion __P((REGINFO *));
 */
int
__db_unmapregion(infop)
    REGINFO *infop;
{
    int called, ret;

    called = 0;
    ret = EINVAL;

    if (__db_jump.j_unmap != NULL)
        return (__db_jump.j_unmap(infop->addr, infop->size));

#ifdef HAVE_SHMGET
    if (infop->segid != INVALID_SEGID) {
        called = 1;
        ret = shmdt(infop->addr) ? errno : 0;
    }
#endif
#ifdef HAVE_MMAP
    if (!called) {
        called = 1;
        ret = munmap(infop->addr, infop->size) ? errno : 0;
    }
#endif
    return (ret);
}

/*
 * __db_unlinkregion --
 *  Remove the shared memory region.
 *
 * PUBLIC: int __db_unlinkregion __P((char *, REGINFO *));
 */
int
__db_unlinkregion(name, infop)
    char *name;
    REGINFO *infop;
{
    int called, ret;

    called = 0;
    ret = EINVAL;

    if (__db_jump.j_runlink != NULL)
        return (__db_jump.j_runlink(name));

#ifdef HAVE_SHMGET
    if (infop->segid != INVALID_SEGID) {
        called = 1;
        ret = shmctl(infop->segid, IPC_RMID, NULL) ? errno : 0;
    }
#endif
#ifdef HAVE_MMAP
    COMPQUIET(infop, NULL);
    if (!called) {
        called = 1;
        ret = 0;
    }
#endif
    return (ret);
}

/*
 * __db_mapfile --
 *  Map in a shared memory file.
 *
 * PUBLIC: int __db_mapfile __P((char *, int, size_t, int, void **));
 */
int
__db_mapfile(path, fd, len, is_rdonly, addr)
    char *path;
    int fd, is_rdonly;
    size_t len;
    void **addr;
{
    if (__db_jump.j_map != NULL)
        return (__db_jump.j_map(path, fd, len, 0, 0, is_rdonly, addr));

#ifdef HAVE_MMAP
    return (__os_map(path, fd, len, 0, 0, is_rdonly, addr));
#else
    return (EINVAL);
#endif
}

/*
 * __db_unmapfile --
 *  Unmap the shared memory file.
 *
 * PUBLIC: int __db_unmapfile __P((void *, size_t));
 */
int
__db_unmapfile(addr, len)
    void *addr;
    size_t len;
{
    if (__db_jump.j_unmap != NULL)
        return (__db_jump.j_unmap(addr, len));

#ifdef HAVE_MMAP
    return (munmap(addr, len) ? errno : 0);
#else
    return (EINVAL);
#endif
}

#ifdef HAVE_MMAP
/*
 * __os_map --
 *  Call the mmap(2) function.
 */
static int
__os_map(path, fd, len, is_region, is_anonymous, is_rdonly, addr)
    char *path;
    int fd, is_region, is_anonymous, is_rdonly;
    size_t len;
    void **addr;
{
    void *p;
    int flags, prot;

    COMPQUIET(path, NULL);

    /*
     * 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;

    if (is_region && is_anonymous) {
        /*
         * BSD derived systems use MAP_ANON; Digital Unix and HP/UX
         * use MAP_ANONYMOUS.
         */
#ifdef MAP_ANON
        flags |= MAP_ANON;
#endif
#ifdef MAP_ANONYMOUS
        flags |= MAP_ANONYMOUS;
#endif
        fd = -1;
    }
#ifdef MAP_FILE
    if (!is_region || !is_anonymous) {
        /*
         * 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_rdonly)
        flags |= MAP_HASSEMAPHORE;
#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(fd) == -1)
        return(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, fd, (off_t)0)) == (void *)MAP_FAILED)
        return (errno);

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

#ifdef HAVE_SHMGET
/*
 * __os_shmget --
 *  Call the shmget(2) family of functions.
 */
static int
__os_shmget(infop)
    REGINFO *infop;
{
    if (F_ISSET(infop, REGION_CREATED) &&
       (infop->segid = shmget(0, infop->size, IPC_PRIVATE | 0600)) == -1)
        return (errno);

    if ((infop->addr = shmat(infop->segid, NULL, 0)) == (void *)-1) {
        /*
         * If we're trying to join the region and failing, assume
         * that there was a reboot and the region no longer exists.
         */
        if (!F_ISSET(infop, REGION_CREATED))
            errno = EAGAIN;
        return (errno);
    }

    F_SET(infop, REGION_HOLDINGSYS);
    return (0);
}
#endif