ioperm - set port input/output permissions
int ioperm(unsigned long from, unsigned long num, int turn_on);
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
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.
On success, zero is returned. On error, -1 is returned, and errno is set
to indicate the error.
ioperm() is Linux-specific and should not be used in programs intended to
The /proc/ioports file shows the I/O ports that are currently allocated
on the system.
- Invalid values for from or num.
- (on PowerPC) This call is not supported.
- Out of memory.
- The calling thread has insufficient privilege.
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.
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