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S390_STHYI(2)                 System Calls Manual                S390_STHYI(2)

NAME
       s390_sthyi - emulate STHYI instruction

SYNOPSIS
       #include <asm/unistd.h>

       int s390_sthyi(unsigned long function_code, void *resp_buffer,
                      uint64_t *return_code, unsigned long flags);

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:

       0      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 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.

       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 appropriately.

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.

CONFORMING TO
       This Linux-specific system call is available only on the s390 architec-
       ture.

NOTES
       Glibc  does  not provide a wrapper for this system call, use syscall(2)
       to call it.

       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)

COLOPHON
       This page is part of release 5.05 of the Linux  man-pages  project.   A
       description  of  the project, information about reporting bugs, and the
       latest    version    of    this    page,    can     be     found     at
       https://www.kernel.org/doc/man-pages/.

Linux Programmer's Manual         2019-03-06                     S390_STHYI(2)
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON