int memp_open(char *dir, u_int32_t flags, int mode, DB_ENV *dbenv, DB_MPOOL **regionp);
The memp_open function copies a pointer, to the "memory pool" identified by the directory dir, into the memory location referenced by regionp.
If the dir pathname argument is NULL or the DB_MPOOL_PRIVATE flag is set, any necessary temporary files are created as described for the DB_TMP_DIR value in Berkeley DB File Naming. Otherwise, the dir pathname argument is interpreted as described in Berkeley DB File Naming.
The flags and mode arguments specify how files will be opened and/or created if they do not already exist. The flags value is specified by logically OR'ing together one or more of the following values:
All files created by the memory pool subsystem (other than files created by the memp_fopen function, which are separately specified) are created with mode mode (as described in chmod(2)) and modified by the process' umask value at the time of creation (see umask(2)))). The group ownership of created files is based on the system and directory defaults, and is not further specified by Berkeley DB.
The memory pool subsystem is configured based on the dbenv argument to memp_open which is a pointer to a structure of type DB_ENV. Applications normally use the same DB_ENV structure (initialized by db_appinit) as an argument to all of the subsystems in the Berkeley DB package.
References to the DB_ENV structure are maintained by Berkeley DB, so it may not be discarded until the last close function, corresponding to an open function for which it was an argument, has returned. To ensure compatibility with future releases of Berkeley DB, all fields of the DB_ENV structure that are not explicitly set should be initialized to 0 before the first time the structure is used. Do this by declaring the structure external or static, or by calling one of the C library routines bzero(3) or memset(3).
The fields of the DB_ENV structure used by memp_open are described below. If dbenv is NULL or any of its fields are set to 0, defaults appropriate for the system are used where possible.
The following fields in the DB_ENV structure may be initialized before calling memp_open:
For information on tuning the Berkeley DB cache size, see Selecting a cache size.
The memp_open function returns the value of errno on failure, and 0 on success.
The memp_open function may fail and return errno for any of the errors specified for the following Berkeley DB and C library functions: DBmemp->pgin(3), DBmemp->pgout(3), abort(3), close(3), db_version, dbenv->db_paniccall(3), fcntl(3), fflush(3), fprintf(3), free(3), fstat(3), fsync(3), getenv(3), getpid(3), getuid(3), isdigit(3), log_compare, log_flush, lseek(3), malloc(3), memcmp(3), memcpy(3), memp_close, memp_unlink, memset(3), mmap(3), munmap(3), open(3), pread(3), pstat_getdynamic(3), pwrite(3), read(3), shmat(3), shmctl(3), shmdt(3), sigfillset(3), sigprocmask(3), stat(3), strerror(3), strlen(3), sysconf(3), time(3), unlink(3), vfprintf(3), vsnprintf(3), and write(3).
In addition, the memp_open function may fail and return errno for the following conditions:
The DB_THREAD flag was specified and spinlocks are not implemented for this architecture.
A NULL pathname was specified without the DB_MPOOL_PRIVATE flag.
The specified cache size was impossibly small.