iopl(2) - f7

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 current process, as spec‐
15       ified in level.
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17       This call is necessary to allow 8514-compatible X servers to run  under
18       Linux.   Since  these  X servers require access to all 65536 I/O ports,
19       the ioperm() call is not sufficient.
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21       In addition to granting unrestricted I/O  port  access,  running  at  a
22       higher  I/O  privilege  level also allows the process to disable inter‐
23       rupts.  This will probably crash the system, and is not recommended.
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25       Permissions are inherited by fork() and exec().
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27       The I/O privilege level for a normal process is 0.
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29       This call is mostly for the i386 architecture.  On many other architec‐
30       tures it does not exist or will always return an error.
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RETURN VALUE

33       On  success,  zero is returned.  On error, -1 is returned, and errno is
34       set appropriately.
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ERRORS

37       EINVAL level is greater than 3.
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39       ENOSYS This call is unimplemented.
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41       EPERM  The calling process has insufficient privilege to  call  iopl();
42              the CAP_SYS_RAWIO capability is required.
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CONFORMING TO

45       iopl()  is  Linux specific and should not be used in processes intended
46       to be portable.
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NOTES

49       Libc5 treats it as a system call and has  a  prototype  in  <unistd.h>.
50       Glibc1  does  not  have  a  prototype.  Glibc2  has a prototype both in
51       <sys/io.h> and in <sys/perm.h>.  Avoid the latter, it is  available  on
52       i386 only.
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