s390_sthyi(2) — Linux manual page

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
       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.

       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
       instruction, 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
       currently 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.

STANDARDS

       Linux on s390.

HISTORY

       Linux 4.15.

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 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

       syscall(2)

COLOPHON

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Linux man-pages 6.9.1          2024-05-02                  s390_sthyi(2)

Pages that refer to this page: syscalls(2)

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