int iopl(int level);
描述iopl() 改变当前进程的I/ O特权级别，在级别 level 指定。 .
This call is necessary to allow 8514-compatible X servers to run under Linux. Since these X servers require access to all 65536 I/O ports, the ioperm() call is not sufficient.
In addition to granting unrestricted I/O port access, running at a higher I/O privilege level also allows the process to disable interrupts. This will probably crash the system, and is not recommended.
Permissions are inherited by fork() and exec().
对于一个正常的过程I / O的优先级为0。
返回值On success, zero is returned. On error, -1 is returned, and errno is set appropriately.
|EINVAL||level is greater than 3.|
|ENOSYS||This call is unimplemented.|
|EPERM||The calling process has insufficient privilege to call iopl(); theCAP_SYS_RAWIO capability is required.|