int iopl(int level);
iopl() changes the I/O privilege level of the calling process, as spec-
ified by the two least significant bits in level.
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(2) 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 inter-
rupts. This will probably crash the system, and is not recommended.
Permissions are inherited by fork(2) and execve(2).
The I/O privilege level for a normal process is 0.
This call is mostly for the i386 architecture. On many other architec-
tures it does not exist or will always return an error.
On success, zero is returned. On error, -1 is returned, and errno is
EINVAL level is greater than 3.
ENOSYS This call is unimplemented.
EPERM The calling process has insufficient privilege to call iopl();
the CAP_SYS_RAWIO capability is required to raise the I/O privi-
lege level above its current value.
iopl() is Linux-specific and should not be used in programs that are
intended to be portable.
Libc5 treats it as a system call and has a prototype in <unistd.h>.
Glibc1 does not have a prototype. Glibc2 has a prototype both in
<sys/io.h> and in <sys/perm.h>. Avoid the latter, it is available on
ioperm(2), outb(2), capabilities(7)
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