2. System calls (functions provided by the kernel)
IOPLSection: Linux Programmer's Manual (2)
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NAMEiopl - change I/O privilege level
DESCRIPTIONiopl() 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 VALUEOn success, zero is returned. On error, -1 is returned, and errno is set appropriately.
- level is greater than 3.
- This call is unimplemented.
- 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.
CONFORMING TOiopl() is Linux-specific and should not be used in programs that are intended to be portable.
NOTESGlibc2 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.
SEE ALSOioperm(2), outb(2), capabilities(7)
COLOPHONThis page is part of release 5.10 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
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