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 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:

       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 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 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 architecture.

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 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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