man2/s390_sthyi.2

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   2 .\" Author: QingFeng Hao <haoqf@linux.vnet.ibm.com>
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  25 .TH S390_STHYI 2 2020-04-11 "Linux Programmer's Manual"
  26 .SH NAME
  27 s390_sthyi \- emulate STHYI instruction
  28 .SH SYNOPSIS
  29 .nf
  30 .B #include <asm/unistd.h>
  31 .PP
  32 .BI "int s390_sthyi(unsigned long " function_code ", void *" resp_buffer ",
  33 .BI "               uint64_t *" return_code ", unsigned long " flags ");
  34 .fi
  35 .SH DESCRIPTION
  36 The
  37 .BR s390_sthyi ()
  38 system call emulates the STHYI (Store Hypervisor Information) instruction.
  39 It provides hardware resource information for the machine and its
  40 virtualization levels.
  41 This includes CPU type and capacity, as well as the machine model and
  42 other metrics.
  43 .PP
  44 The
  45 .I function_code
  46 argument indicates which function to perform.
  47 The following code(s) are supported:
  48 .TP
  49 0
  50 Return CP (Central Processor) and IFL (Integrated Facility for Linux)
  51 capacity information.
  52 .PP
  53 The
  54 .I resp_buffer
  55 argument specifies the address of a response buffer.
  56 When the
  57 .I function_code
  58 is 0, the buffer must be one page (4K) in size.
  59 If the system call returns 0,
  60 the response buffer will be filled with CPU capacity information.
  61 Otherwise, the response buffer's content is unchanged.
  62 .PP
  63 The
  64 .I return_code
  65 argument stores the return code of the STHYI instruction,
  66 using one of the following values:
  67 .TP
  68 0
  69 Success.
  70 .TP
  71 4
  72 Unsupported function code.
  73 .PP
  74 For further details about
  75 .IR return_code ,
  76 .IR function_code ,
  77 and
  78 .IR resp_buffer ,
  79 see the reference given in NOTES.
  80 .PP
  81 The
  82 .I flags
  83 argument is provided to allow for future extensions and currently
  84 must be set to 0.
  85 .SH RETURN VALUE
  86 On success (that is: emulation succeeded), the return value of
  87 .BR s390_sthyi ()
  88 matches the condition code of the STHYI instructions, which is a value
  89 in the range [0..3].
  90 A return value of 0 indicates that CPU capacity information is stored in
  91 .IR *resp_buffer .
  92 A return value of 3 indicates "unsupported function code" and the content of
  93 .IR *resp_buffer
  94 is unchanged.
  95 The return values 1 and 2 are reserved.
  96 .PP
  97 On error, \-1 is returned, and
  98 .IR errno
  99 is set appropriately.
 100 .SH ERRORS
 101 .TP
 102 .B EFAULT
 103 The value specified in
 104 .I resp_buffer
 105 or
 106 .I return_code
 107 is not a valid address.
 108 .TP
 109 .B EINVAL
 110 The value specified in
 111 .I flags
 112 is nonzero.
 113 .TP
 114 .B ENOMEM
 115 Allocating memory for handling the CPU capacity information failed.
 116 .TP
 117 .B EOPNOTSUPP
 118 The value specified in
 119 .I function_code
 120 is not valid.
 121 .SH VERSIONS
 122 This system call is available since Linux 4.15.
 123 .SH CONFORMING TO
 124 This Linux-specific system call is available only on the s390 architecture.
 125 .SH NOTES
 126 Glibc does not provide a wrapper for this system call, use
 127 .BR syscall (2)
 128 to call it.
 129 .PP
 130 For details of the STHYI instruction, see
 131 .UR https://www.ibm.com\:/support\:/knowledgecenter\:/SSB27U_6.3.0\:/com.ibm.zvm.v630.hcpb4\:/hcpb4sth.htm
 132 the documentation page
 133 .UE .
 134 .PP
 135 When the system call interface is used, the response buffer doesn't
 136 have to fulfill alignment requirements described in the STHYI
 137 instruction definition.
 138 .PP
 139 The kernel caches the response (for up to one second, as of Linux 4.16).
 140 Subsequent system call invocations may return the cached response.
 141 .SH SEE ALSO
 142 .BR syscall (2)