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Annotated edit history of iopl(2) version 2, including all changes. View license author blame.
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1 perry 1 !!NAME
2 PerryLorier 2 iopl - change I/O privilege level
1 perry 3
4 !!SYNOPSIS
2 PerryLorier 5 __#include <sys/io.h>__
1 perry 6
2 PerryLorier 7 __int iopl(int__ ''level''__);__
1 perry 8 !!DESCRIPTION
2 PerryLorier 9 iopl(2) changes the I/O privilege level of the current process, as specified in ''level''.
1 perry 10
2 PerryLorier 11 This call is necessary to allow 8514-compatible X servers to run under Linux. Since these X servers require access to all 65536 I/O ports, the ioperm(2) call is not
1 perry 12 sufficient.
13
2 PerryLorier 14 In addition to granting unrestricted I/O port access, running at a higher I/O privilege level also allows the process to disable interrupts. This will probably crash the system, and is not recommended.
1 perry 15
16 Permissions are inherited by fork and exec.
17
2 PerryLorier 18 The I/O privilege level for a normal process is 0.
1 perry 19
20 !!RETURN VALUE
2 PerryLorier 21 On success, zero is returned. On error, -1 is returned, and ''errno'' is set appropriately.
1 perry 22 !!ERRORS
2 PerryLorier 23 ;[EINVAL]: ''level'' is greater than 3.
24 ;[EPERM]: The current user is not the super-user.
1 perry 25
26 !!NOTES FROM THE KERNEL SOURCE
2 PerryLorier 27 iopl(2) has to be used when you want to access the I/O ports beyond the 0x3ff range: to get the full 65536 ports bitmapped you'd need 8kB of bitmaps/process, which is a bit excessive.
1 perry 28
29 !!CONFORMING TO
2 PerryLorier 30 iopl(2) is Linux specific and should not be used in processes intended to be portable.
1 perry 31
32 !!COMPATIBILITY
2 PerryLorier 33 Under libc5, the prototype for __iopl__() was given in ''<unistd.h>''. Glibc1 does not have a prototype. Glibc2 has a prototype both in <sys/io.h> and in <sys/perm.h>. Avoid the latter, it is available on i386 only.
1 perry 34
35 !!SEE ALSO
36 ioperm(2)
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