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s390_sthyi(2) — Linux manual page

s390_sthyi(2)              System Calls Manuals390_sthyi(2)

NAME        top

       s390_sthyi - emulate STHYI instruction

LIBRARY        top

       Standard C library (libc,-lc)

SYNOPSIS        top

#include <asm/sthyi.h>/* Definition ofSTHYI_*constants */#include <sys/syscall.h>/* Definition ofSYS_*constants */#include <unistd.h>int syscall(SYS_s390_sthyi, unsigned longfunction_code,void *resp_buffer, uint64_t *return_code,unsigned longflags);Note: glibc provides no wrapper fors390_sthyi(), necessitating       the use ofsyscall(2).

DESCRIPTION        top

       Thes390_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.       Thefunction_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.       Theresp_buffer argument specifies the address of a response       buffer.  When thefunction_code isSTHYI_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.       Thereturn_code argument stores the return code of the STHYI       instruction, using one of the following values:       0      Success.       4      Unsupported function code.       For further details aboutreturn_code,function_code, andresp_buffer, see the reference given in NOTES.       Theflags argument is provided to allow for future extensions and       currently must be set to 0.

RETURN VALUE        top

       On success (that is: emulation succeeded), the return value ofs390_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, anderrno is set to indicate the error.

ERRORS        top

EFAULTThe value specified inresp_buffer orreturn_code is not a              valid address.EINVALThe value specified inflags is nonzero.ENOMEMAllocating memory for handling the CPU capacity information              failed.EOPNOTSUPP              The value specified infunction_code is not valid.

STANDARDS        top

       Linux on s390.

HISTORY        top

       Linux 4.15.

NOTES        top

       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 instruction definition.       The kernel caches the response (for up to one second, as of Linux       4.16).  Subsequent system call invocations may return the cached       response.

SEE ALSO        top

syscall(2)

COLOPHON        top

       This page is part of theman-pages (Linux kernel and C library       user-space interface documentation) project.  Information about       the project can be found at        ⟨https://www.kernel.org/doc/man-pages/⟩.  If you have a bug report       for this manual page, see       ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.       This page was obtained from the tarball man-pages-6.15.tar.gz       fetched from       ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on       2025-08-11.  If you discover any rendering problems in this HTML       version of the page, or you believe there is a better or more up-       to-date source for the page, or you have corrections or       improvements to the information in this COLOPHON (which isnot       part of the original manual page), send a mail to       man-pages@man7.orgLinux man-pages 6.15            2025-05-17s390_sthyi(2)

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