s390_sthyi(2) System Calls Manual s390_sthyi(2)
NAME
s390_sthyi - emulate STHYI instruction
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#include <asm/sthyi.h> /* Definition of STHYI_* constants */
#include <sys/syscall.h> /* Definition of SYS_* constants */
#include <unistd.h>
int syscall(SYS_s390_sthyi, unsigned long function_code,
void *resp_buffer, uint64_t *return_code,
unsigned long flags);
Note: glibc provides no wrapper for s390_sthyi(), necessitating the use
of syscall(2).
DESCRIPTION
The s390_sthyi() system call emulates the STHYI (Store Hypervisor In-
formation) 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.
The function_code argument indicates which function to perform. The
following code(s) are supported:
STHYI_FC_CP_IFL_CAP
Return CP (Central Processor) and IFL (Integrated Facility for
Linux) capacity information.
The resp_buffer argument specifies the address of a response buffer.
When the function_code is STHYI_FC_CP_IFL_CAP, 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.
The return_code argument stores the return code of the STHYI instruc-
tion, using one of the following values:
0 Success.
4 Unsupported function code.
For further details about return_code, function_code, and resp_buffer,
see the reference given in NOTES.
The flags argument is provided to allow for future extensions and cur-
rently must be set to 0.
RETURN VALUE
On success (that is: emulation succeeded), the return value of
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 *resp_buffer. A return
value of 3 indicates "unsupported function code" and the content of
*resp_buffer is unchanged. The return values 1 and 2 are reserved.
On error, -1 is returned, and errno is set to indicate the error.
ERRORS
EFAULT The value specified in resp_buffer or return_code is not a valid
address.
EINVAL The value specified in flags is nonzero.
ENOMEM Allocating memory for handling the CPU capacity information
failed.
EOPNOTSUPP
The value specified in function_code is not valid.
VERSIONS
This system call is available since Linux 4.15.
STANDARDS
This Linux-specific system call is available only on the s390 architec-
ture.
NOTES
For details of the STHYI instruction, see the documentation page
⟨https://www.ibm.com/support/knowledgecenter/SSB27U_6.3.0
/com.ibm.zvm.v630.hcpb4/hcpb4sth.htm⟩.
When the system call interface is used, the response buffer doesn't
have to fulfill alignment requirements described in the STHYI instruc-
tion definition.
The kernel caches the response (for up to one second, as of Linux
4.16). Subsequent system call invocations may return the cached re-
sponse.
SEE ALSO
syscall(2)
Linux man-pages 6.03 2022-10-30 s390_sthyi(2)
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