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IOPL(2) Linux Programmer's Manual IOPL(2)
iopl - change I/O privilege level
int iopl(int level);
iopl() changes the I/O privilege level of the calling process, as specified 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 interrupts. 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 architectures it does not
exist or will always return an error.
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(); the CAP_SYS_RAWIO
capability is required to raise the I/O privilege level above its current value.
iopl() is Linux-specific and should not be used in programs that are intended to be porta-
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 i386 only.
ioperm(2), outb(2), capabilities(7)
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Linux 2013-03-15 IOPL(2)
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