# s390_sthyi

## 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.
    


## 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.
    


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