mkmap_db.c

[詳解]

/*++
/* NAME
/*  mkmap_db 3
/* SUMMARY
/*  create or open database, DB style
/* SYNOPSIS
/*  #include <mkmap.h>
/*
/*  MKMAP   *mkmap_hash_open(path)
/*  const char *path;
/*
/*  MKMAP   *mkmap_btree_open(path)
/*  const char *path;
/* DESCRIPTION
/*  This module implements support for creating DB databases.
/*
/*  mkmap_hash_open() and mkmap_btree_open() take a file name,
/*  append the ".db" suffix, and do whatever initialization is
/*  required before the Berkeley DB open routine is called.
/*
/*  All errors are fatal.
/* SEE ALSO
/*  dict_db(3), DB dictionary interface.
/* LICENSE
/* .ad
/* .fi
/*  The Secure Mailer license must be distributed with this software.
/* AUTHOR(S)
/*  Wietse Venema
/*  IBM T.J. Watson Research
/*  P.O. Box 704
/*  Yorktown Heights, NY 10598, USA
/*--*/

/* System library. */

#include <sys_defs.h>
#include <sys/stat.h>
#include <unistd.h>
#include <errno.h>

/* Utility library. */

#include <msg.h>
#include <mymalloc.h>
#include <stringops.h>
#include <dict.h>
#include <dict_db.h>
#include <myflock.h>
#include <warn_stat.h>

/* Global library. */

#include <mail_params.h>

/* Application-specific. */

#include "mkmap.h"

#ifdef HAS_DB
#ifdef PATH_DB_H
#include PATH_DB_H
#else
#include <db.h>
#endif

typedef struct MKMAP_DB {
    MKMAP   mkmap;          /* parent class */
    char   *lock_file;          /* path name */
    int     lock_fd;            /* -1 or open locked file */
} MKMAP_DB;

/* mkmap_db_after_close - clean up after closing database */

static void mkmap_db_after_close(MKMAP *mp)
{
    MKMAP_DB *mkmap = (MKMAP_DB *) mp;

    if (mkmap->lock_fd >= 0 && close(mkmap->lock_fd) < 0)
    msg_warn("close %s: %m", mkmap->lock_file);
    myfree(mkmap->lock_file);
}

/* mkmap_db_after_open - lock newly created database */

static void mkmap_db_after_open(MKMAP *mp)
{
    MKMAP_DB *mkmap = (MKMAP_DB *) mp;

    if (mkmap->lock_fd < 0) {
    if ((mkmap->lock_fd = open(mkmap->lock_file, O_RDWR, 0644)) < 0)
        msg_fatal("open lockfile %s: %m", mkmap->lock_file);
    if (myflock(mkmap->lock_fd, INTERNAL_LOCK, MYFLOCK_OP_EXCLUSIVE) < 0)
        msg_fatal("lock %s: %m", mkmap->lock_file);
    }
}

/* mkmap_db_before_open - lock existing database */

static MKMAP *mkmap_db_before_open(const char *path,
                      DICT *(*db_open) (const char *, int, int))
{
    MKMAP_DB *mkmap = (MKMAP_DB *) mymalloc(sizeof(*mkmap));
    struct stat st;

    /*
     * Override the default per-table cache size for map (re)builds.
     * 
     * db_cache_size" is defined in util/dict_db.c and defaults to 128kB, which
     * works well for the lookup code.
     * 
     * We use a larger per-table cache when building ".db" files. For "hash"
     * files performance degrades rapidly unless the memory pool is O(file
     * size).
     * 
     * For "btree" files performance is good with sorted input even for small
     * memory pools, but with random input degrades rapidly unless the memory
     * pool is O(file size).
     * 
     * XXX This should be specified via the DICT interface so that the buffer
     * size becomes an object property, instead of being specified by poking
     * a global variable so that it becomes a class property.
     */
    dict_db_cache_size = var_db_create_buf;

    /*
     * Fill in the generic members.
     */
    mkmap->lock_file = concatenate(path, ".db", (char *) 0);
    mkmap->mkmap.open = db_open;
    mkmap->mkmap.after_open = mkmap_db_after_open;
    mkmap->mkmap.after_close = mkmap_db_after_close;

    /*
     * Unfortunately, not all systems that might support db databases do
     * support locking on open(), so we open the file before updating it.
     * 
     * XXX Berkeley DB 4.1 refuses to open a zero-length file. This means we can
     * open and lock only an existing file, and that we must not truncate it.
     */
    if ((mkmap->lock_fd = open(mkmap->lock_file, O_RDWR, 0644)) < 0) {
    if (errno != ENOENT)
        msg_fatal("open %s: %m", mkmap->lock_file);
    }

    /*
     * Get an exclusive lock - we're going to change the database so we can't
     * have any spectators.
     * 
     * XXX Horror. Berkeley DB 4.1 refuses to open a zero-length file. This
     * means that we must examine the size while the file is locked, and that
     * we must unlink a zero-length file while it is locked. Avoid a race
     * condition where two processes try to open the same zero-length file
     * and where the second process ends up deleting the wrong file.
     */
    else {
    if (myflock(mkmap->lock_fd, INTERNAL_LOCK, MYFLOCK_OP_EXCLUSIVE) < 0)
        msg_fatal("lock %s: %m", mkmap->lock_file);
    if (fstat(mkmap->lock_fd, &st) < 0)
        msg_fatal("fstat %s: %m", mkmap->lock_file);
    if (st.st_size == 0) {
        if (st.st_nlink > 0) {
        if (unlink(mkmap->lock_file) < 0)
            msg_fatal("cannot remove zero-length database file %s: %m",
                  mkmap->lock_file);
        msg_warn("removing zero-length database file: %s",
             mkmap->lock_file);
        }
        close(mkmap->lock_fd);
        mkmap->lock_fd = -1;
    }
    }

    return (&mkmap->mkmap);
}

/* mkmap_hash_open - create or open hashed DB file */

MKMAP  *mkmap_hash_open(const char *path)
{
    return (mkmap_db_before_open(path, dict_hash_open));
}

/* mkmap_btree_open - create or open btree DB file */

MKMAP  *mkmap_btree_open(const char *path)
{
    return (mkmap_db_before_open(path, dict_btree_open));
}

#endif