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# iopl() - Unix, Linux System Call

# NAME

iopl - change I/O privilege level

# SYNOPSIS

#include <sys/io.h>

int iopl(int level);

# DESCRIPTION

iopl() changes the I/O privilege level of the current process, as specified 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() 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().

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.

# RETURN VALUE

On success, zero is returned. On error, -1 is returned, and errno is set appropriately.

# ERRORS

Tag | Description
--- | ---
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.

# CONFORMING TO

iopl() is Linux specific and should not be used in processes intended to be portable.

# NOTES

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.

# SEE ALSO

- ioperm (2)

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