ioperm(2)

1ioperm(2)                     System Calls Manual                    ioperm(2)
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NAME

6       ioperm - set port input/output permissions
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LIBRARY

9       Standard C library (libc, -lc)
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SYNOPSIS

12       #include <sys/io.h>
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14       int ioperm(unsigned long from, unsigned long num, int turn_on);
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DESCRIPTION

17       ioperm()  sets  the  port access permission bits for the calling thread
18       for num bits starting from port address from.  If turn_on  is  nonzero,
19       then permission for the specified bits is enabled; otherwise it is dis‐
20       abled.  If turn_on is nonzero, the calling thread  must  be  privileged
21       (CAP_SYS_RAWIO).
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23       Before  Linux  2.6.8, only the first 0x3ff I/O ports could be specified
24       in this manner.  For more ports, the iopl(2) system call had to be used
25       (with  a level argument of 3).  Since Linux 2.6.8, 65,536 I/O ports can
26       be specified.
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28       Permissions are inherited by the child  created  by  fork(2)  (but  see
29       NOTES).  Permissions are preserved across execve(2); this is useful for
30       giving port access permissions to unprivileged programs.
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32       This call is mostly for the i386 architecture.  On many other architec‐
33       tures it does not exist or will always return an error.
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RETURN VALUE

36       On  success,  zero is returned.  On error, -1 is returned, and errno is
37       set to indicate the error.
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ERRORS

40       EINVAL Invalid values for from or num.
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42       EIO    (on PowerPC) This call is not supported.
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44       ENOMEM Out of memory.
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46       EPERM  The calling thread has insufficient privilege.
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VERSIONS

49       glibc has an ioperm() prototype both in <sys/io.h> and in <sys/perm.h>.
50       Avoid the latter, it is available on i386 only.
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STANDARDS

53       Linux.
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HISTORY

56       Before  Linux 2.4, permissions were not inherited by a child created by
57       fork(2).
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NOTES

60       The /proc/ioports file shows the I/O ports that are currently allocated
61       on the system.
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