erlang如何打开设备文件?

> file:open("/dev/urandom", [read,raw]).
{error,eisdir}

Google了下,得到:
"The efile driver expects the file to be regular in the
sense that operations won't block (i.e. a "fast" device). If one could
open e.g a tape drive and write to it, the whole erlang machine will
block for several seconds/minutes/hours, which is not especially nice.
If one wants to operate on special files, one have to either write a
"port program" (which will spin in a separate process) or write a
loadable driver, which uses threads or the io multiplexing mechanisms to
avoid hanging the emulator."

难道操作设备文件这么麻烦 ?!

int
efile_openfile(Efile_error* errInfo, /* Where to return error codes. */
       char* name, /* Name of directory to open. */
       int flags, /* Flags to user for opening. */
       int* pfd, /* Where to store the file
   descriptor. */
       Sint64 *pSize) /* Where to store the size of the
   file. */
{
。。。。


if (stat(name, &statbuf) >= 0 && !ISREG(statbuf)) {
#if !defined(VXWORKS) && !defined(OSE)
/*
* For UNIX only, here is some ugly code to allow
* /dev/null to be opened as a file.
*
* Assumption: The i-node number for /dev/null cannot be zero.
*/
static ino_t dev_null_ino = 0;

if (dev_null_ino == 0) {
    struct stat nullstatbuf;
   
    if (stat("/dev/null", &nullstatbuf) >= 0) {
dev_null_ino = nullstatbuf.st_ino;
    }
}p den

if (!(dev_null_ino && statbuf.st_ino == dev_null_ino)) {
#endif
    errno = EISDIR;
    return check_error(-1, errInfo);
#if !defined(VXWORKS) && !defined(OSE)
}
#endif
    }

。。。
}

也就是说如果打开的不是 regular文件 或者/dev/null, 那么文件打开失败！

设计的用意就是怕设备操作block了调度器，因为之前erlang支持smp之前 只有唯一的一个调度器 阻塞了系统就挂了!