iopl - change I/O privilege level
Standard C library (
libc,
-lc)
#include <sys/io.h>
[[deprecated]] int iopl(int level);
iopl() changes the I/O privilege level of the calling thread, as
specified by the two least significant bits in
level.
The I/O privilege level for a normal thread is 0. Permissions are inherited from
parents to children.
This call is deprecated, is significantly slower than
ioperm(2), and is
only provided for older X servers which require access to all 65536 I/O ports.
It 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
to indicate the error.
- EINVAL
-
level is greater than 3.
- ENOSYS
- This call is unimplemented.
- EPERM
- The calling thread 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 portable.
glibc2 has a prototype both in
<sys/io.h> and in
<sys/perm.h>. Avoid the latter, it is available on i386 only.
Prior to Linux 5.5
iopl() allowed the thread to disable interrupts while
running at a higher I/O privilege level. This will probably crash the system,
and is not recommended.
Prior to Linux 3.7, on some architectures (such as i386), permissions
were inherited by the child produced by
fork(2) and were
preserved across
execve(2). This behavior was inadvertently changed in
Linux 3.7, and won't be reinstated.
ioperm(2),
outb(2),
capabilities(7)