IOPLSection: Linux Programmer's Manual (2)
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NAMEiopl - change I/O privilege level
DESCRIPTIONiopl() changes the I/O privilege level of the current process, as specified in level.
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 sufficient.
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.
The I/O privilege level for a normal process is 0.
RETURN VALUEOn success, zero is returned. On error, -1 is returned, and errno is set appropriately.
- level is greater than 3.
- This call is unimplemented.
- The calling process has insufficient privilege to call iopl(); the CAP_SYS_RAWIO capability is required.
CONFORMING TOiopl() is Linux specific and should not be used in processes intended to be portable.
NOTESLibc5 treats it as a system call and has a prototype 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.
SEE ALSOioperm(2), capabilities(7)