1IOPL(2)                    Linux Programmer's Manual                   IOPL(2)
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NAME

6       iopl - change I/O privilege level
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SYNOPSIS

9       #include <sys/io.h>
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11       int iopl(int level);
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DESCRIPTION

14       iopl() changes the I/O privilege level of the calling thread, as speci‐
15       fied by the two least significant bits in level.
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17       The I/O privilege level for a normal thread is 0.  Permissions are  in‐
18       herited from parents to children.
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20       This call is deprecated, is significantly slower than ioperm(2), and is
21       only provided for older X servers which require access to all 65536 I/O
22       ports.   It  is mostly for the i386 architecture.  On many other archi‐
23       tectures it does not exist or will always return an error.
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RETURN VALUE

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

30       EINVAL level is greater than 3.
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32       ENOSYS This call is unimplemented.
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34       EPERM  The  calling  thread  has insufficient privilege to call iopl();
35              the CAP_SYS_RAWIO capability is required to raise the I/O privi‐
36              lege level above its current value.
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CONFORMING TO

39       iopl()  is  Linux-specific  and should not be used in programs that are
40       intended to be portable.
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NOTES

43       Glibc2 has a prototype both in <sys/io.h> and in  <sys/perm.h>.   Avoid
44       the latter, it is available on i386 only.
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46       Prior  to  Linux  5.5  iopl()  allowed the thread to disable interrupts
47       while running at a higher I/O  privilege  level.   This  will  probably
48       crash the system, and is not recommended.
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50       Prior  to  Linux 3.7, on some architectures (such as i386), permissions
51       were inherited by the child produced  by  fork(2)  and  were  preserved
52       across  execve(2).   This  behavior  was inadvertently changed in Linux
53       3.7, and won't be reinstated.
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SEE ALSO

56       ioperm(2), outb(2), capabilities(7)
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COLOPHON

59       This page is part of release 5.13 of the Linux  man-pages  project.   A
60       description  of  the project, information about reporting bugs, and the
61       latest    version    of    this    page,    can     be     found     at
62       https://www.kernel.org/doc/man-pages/.
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66Linux                             2021-03-22                           IOPL(2)
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