man-pages/man2/s390_sthyi.2

.\" Copyright IBM Corp. 2017
.\" Author: QingFeng Hao <haoqf@linux.vnet.ibm.com>
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.TH S390_STHYI 2 2017-09-21 "Linux Programmer's Manual"
.SH NAME
s390_sthyi \- emulate STHYI instruction
.SH SYNOPSIS
.nf
.B #include <asm/unistd.h>
.PP
.BI "int s390_sthyi(unsigned long " function_code ", void *" buffer ",
.BI "               uint64_t *" return_code ", unsigned long " flags ");
.fi
.SH DESCRIPTION
The
.BR s390_sthyi ()
system call emulates the STHYI (Store Hypervisor Information) instruction.
It provides hardware resource information for the machine and its virtualization
levels. This includes CPU type and capacity, as well as the machine model and
other metrics.
.PP
The
.I function_code
argument indicates which function to perform.
The following code(s) are supported:
.TP
0
Return CP (Central Processor) and IFL (Integrated Facility for Linux)
capacity information.
.PP
The
.I buffer 
argument specifies the address of a response buffer. If the system
call returns 0, the response buffer will be filled with CPU capacity
information. Otherwise, the response buffer's content is unchanged.
.PP
The
.I return_code
argument stores the return code of the STHYI instruction, using one
of the
following values:
.TP 8
0
Success.
.TP
4
Unsupported function code.
.PP
For further details about
.IR return_code ,
.IR function_code ,
and
.IR buffer ,
please see section
CONFORMING TO
below.
.PP
The
.I flags
argument is provided to allow for future extensions and currently
must be set to 0.
.SH RETURN VALUE
On success, the return value of
.BR s390_sthyi ()
matches the condition code of the STHYI instructions, which is a value
between 0-3 (that is: emulation succeeded).
Return value of 0 indicates that CPU capacity information is stored to
.IR buffer .
Return value of 3 indicates "unsupported function code" and buffer's
content is unchanged.
Return value of 1 and 2 are reserved.
.PP
On error, \-1 is returned, and
.IR errno
is set appropriately.
.SH ERRORS
.TP
.B EINVAL
The value specified in
.I flags
is non-zero.
.TP
.B EOPNOTSUPP
The value specified in
.I function_code 
is not a valid value.
.TP
.B EFAULT
The value specified in
.I buffer 
or
.I return_code
is not a valid address.
.TP
.B ENOMEM
Allocating memory for handling the CPU capacity information failed.
.SH VERSIONS
This system call is available since Linux 4.15.
.SH CONFORMING TO
This Linux-specific system call is available only on the s390 architecture.
For details about the STHYI instruction, see
https://www.ibm.com/support/knowledgecenter/SSB27U_6.3.0/com.ibm.zvm.v630.hcpb4/hcpb4sth.htm
.SH NOTES
Glibc does not provide a wrapper for this system call, use
.BR syscall (2)
to call it.
.SH SEE ALSO
.BR syscall (2)