.\" Copyright IBM Corp. 2017
.\" Author: QingFeng Hao <haoqf@linux.vnet.ibm.com>
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.TH S390_STHYI 2 2018-02-02 "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 *" resp_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 resp_buffer
argument specifies the address of a response buffer.
When the
.I function_code
is 0, the buffer must be one page (4K) in size.
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 resp_buffer ,
see the reference given in NOTES.
.PP
The
.I flags
argument is provided to allow for future extensions and currently
must be set to 0.
.SH RETURN VALUE
On success (that is: emulation succeeded), the return value of
.BR s390_sthyi ()
matches the condition code of the STHYI instructions, which is a value
in the range [0..3].
A return value of 0 indicates that CPU capacity information is stored in
.IR *resp_buffer .
A return value of 3 indicates "unsupported function code" and the content of
.IR *resp_buffer
is unchanged.
The return values 1 and 2 are reserved.
.PP
On error, \-1 is returned, and
.IR errno
is set appropriately.
.SH ERRORS
.TP
.B EFAULT
The value specified in
.I resp_buffer
or
.I return_code
is not a valid address.
.TP
.B EINVAL
The value specified in
.I flags
is nonzero.
.TP
.B ENOMEM
Allocating memory for handling the CPU capacity information failed.
.TP
.B EOPNOTSUPP
The value specified in
.I function_code
is not valid.
.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.
.SH NOTES
Glibc does not provide a wrapper for this system call, use
.BR syscall (2)
to call it.
.PP
For details of the STHYI instruction, see
.UR https://www.ibm.com\:/support\:/knowledgecenter\:/SSB27U_6.3.0\:/com.ibm.zvm.v630.hcpb4\:/hcpb4sth.htm
the documentation page
.UE .
.PP
When the system call interface is used, the response buffer doesn't
have to fulfill alignment requirements described in the STHYI
instruction definition.
.PP
The kernel caches the response (for up to one second, as of Linux 4.16).
Subsequent system call invocations may return the cached response.
.SH SEE ALSO
.BR syscall (2)