iopl
Section: System Calls (2)
Updated: 202-0-08
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NAME
iopl - change I/O privilege level
LIBRARY
Standard C library
(
libc,~
-lc)
SYNOPSIS
#include <sys/io.h>
[[deprecated]] int iopl(int level);
DESCRIPTION
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.
RETURN VALUE
On success, zero is returned.
On error, -1 is returned, and
errno
is set to indicate the error.
ERRORS
- 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.
VERSIONS
glibc2 has a prototype both in
<sys/io.h>
and in
<sys/perm.h>.
Avoid the latter, it is available on i386 only.
STANDARDS
Linux.
HISTORY
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.
SEE ALSO
ioperm(2),
outb(2),
capabilities(7)
Index
- NAME
-
- LIBRARY
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- VERSIONS
-
- STANDARDS
-
- HISTORY
-
- SEE ALSO
-
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