ioperm(2) System Calls Manual ioperm(2)
NAME
ioperm - set port input/output permissions
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#include <sys/io.h>
int ioperm(unsigned long from, unsigned long num, int turn_on);
DESCRIPTION
ioperm() sets the port access permission bits for the calling thread for
num bits starting from port address from. If turn_on is nonzero, then
permission for the specified bits is enabled; otherwise it is disabled.
If turn_on is nonzero, the calling thread must be privileged
(CAP_SYS_RAWIO).
Before Linux 2.6.8, only the first 0x3ff I/O ports could be specified in
this manner. For more ports, the iopl(2) system call had to be used
(with a level argument of 3). Since Linux 2.6.8, 65,536 I/O ports can
be specified.
Permissions are inherited by the child created by fork(2) (but see
NOTES). Permissions are preserved across execve(2); this is useful for
giving port access permissions to unprivileged programs.
This call is mostly for the i386 architecture. On many other architec-
tures 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 to indicate the error.
ERRORS
EINVAL Invalid values for from or num.
EIO (on PowerPC) This call is not supported.
ENOMEM Out of memory.
EPERM The calling thread has insufficient privilege.
VERSIONS
glibc has an ioperm() prototype both in <sys/io.h> and in <sys/perm.h>.
Avoid the latter, it is available on i386 only.
STANDARDS
Linux.
HISTORY
Before Linux 2.4, permissions were not inherited by a child created by
fork(2).
NOTES
The /proc/ioports file shows the I/O ports that are currently allocated
on the system.
SEE ALSO
iopl(2), outb(2), capabilities(7)
Linux man-pages 6.9.1 2024-05-02 ioperm(2)
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