2. System calls (functions provided by the kernel)
IOPERMSection: Linux Programmer's Manual (2)
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NAMEioperm - set port input/output permissions
SYNOPSIS#include <sys/io.h> /* for glibc */
int ioperm(unsigned long from, unsigned long num, int turn_on);
DESCRIPTIONioperm() 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 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.
- Invalid values for from or num.
- (on PowerPC) This call is not supported.
- Out of memory.
- The calling thread has insufficient privilege.
CONFORMING TOioperm() is Linux-specific and should not be used in programs intended to be portable.
NOTESThe /proc/ioports file shows the I/O ports that are currently allocated on the system.
Before Linux 2.4, permissions were not inherited by a child created by fork(2).
Glibc has an ioperm() prototype both in <sys/io.h> and in <sys/perm.h>. Avoid the latter, it is available on i386 only.
SEE ALSOiopl(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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