man2/kexec_load.2

   1 .\" Copyright (C) 2010 Intel Corporation
   2 .\" Author: Andi Kleen
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  26 .TH KEXEC_LOAD 2 2014-08-19 "Linux" "Linux Programmer's Manual"
  27 .SH NAME
  28 kexec_load, kexec_file_load \- load a new kernel for later execution
  29 .SH SYNOPSIS
  30 .B #include <linux/kexec.h>
  31 .br
  32
  33 .BI "long kexec_load(unsigned long " entry ", unsigned long " nr_segments ","
  34 .br
  35 .BI "                struct kexec_segment *" segments \
  36 ", unsigned long " flags ");"
  37 .br
  38
  39 .BI "int kexec_file_load(int " kernel_fd ", int " initrd_fd ","
  40 .br
  41 .BI "                    unsigned long " cmdline_len  \
  42 ", const char *" cmdline ","
  43 .br
  44 .BI "                    unsigned long " flags ");"
  45
  46 .IR Note :
  47 There are no glibc wrappers for these system calls; see NOTES.
  48 .SH DESCRIPTION
  49 The
  50 .BR kexec_load ()
  51 system call loads a new kernel that can be executed later by
  52 .BR reboot (2).
  53 .PP
  54 The
  55 .I flags
  56 argument is a bit mask that controls the operation of the call.
  57 The following values can be specified in
  58 .IR flags :
  59 .TP
  60 .BR KEXEC_ON_CRASH " (since Linux 2.6.13)"
  61 Execute the new kernel automatically on a system crash.
  62 .\" FIXME Explain in more detail how KEXEC_ON_CRASH is actually used
  63 .TP
  64 .BR KEXEC_PRESERVE_CONTEXT " (since Linux 2.6.27)"
  65 Preserve the system hardware and
  66 software states before executing the new kernel.
  67 This could be used for system suspend.
  68 This flag is available only if the kernel was configured with
  69 .BR CONFIG_KEXEC_JUMP ,
  70 and is effective only if
  71 .I nr_segments
  72 is greater than 0.
  73 .PP
  74 The high-order bits (corresponding to the mask 0xffff0000) of
  75 .I flags
  76 contain the architecture of the to-be-executed kernel.
  77 Specify (OR) the constant
  78 .B KEXEC_ARCH_DEFAULT
  79 to use the current architecture,
  80 or one of the following architecture constants
  81 .BR KEXEC_ARCH_386 ,
  82 .BR KEXEC_ARCH_68K ,
  83 .BR KEXEC_ARCH_X86_64 ,
  84 .BR KEXEC_ARCH_PPC ,
  85 .BR KEXEC_ARCH_PPC64 ,
  86 .BR KEXEC_ARCH_IA_64 ,
  87 .BR KEXEC_ARCH_ARM ,
  88 .BR KEXEC_ARCH_S390 ,
  89 .BR KEXEC_ARCH_SH ,
  90 .BR KEXEC_ARCH_MIPS ,
  91 and
  92 .BR KEXEC_ARCH_MIPS_LE .
  93 The architecture must be executable on the CPU of the system.
  94
  95 The
  96 .I entry
  97 argument is the physical entry address in the kernel image.
  98 The
  99 .I nr_segments
 100 argument is the number of segments pointed to by the
 101 .I segments
 102 pointer;
 103 the kernel imposes an (arbitrary) limit of 16 on the number of segments.
 104 The
 105 .I segments
 106 argument is an array of
 107 .I kexec_segment
 108 structures which define the kernel layout:
 109 .in +4n
 110 .nf
 111
 112 struct kexec_segment {
 113     void   *buf;        /* Buffer in user space */
 114     size_t  bufsz;      /* Buffer length in user space */
 115     void   *mem;        /* Physical address of kernel */
 116     size_t  memsz;      /* Physical address length */
 117 };
 118 .fi
 119 .in
 120 .PP
 121 .\" FIXME Explain the details of how the kernel image defined by segments
 122 .\" is copied from the calling process into previously reserved memory.
 123 The kernel image defined by
 124 .I segments
 125 is copied from the calling process into previously reserved memory.
 126 .SS kexec_file_load()
 127 The
 128 .BR kexec_file_load ()
 129 system call is similar to
 130 .BR kexec_load (),
 131 but it takes a different set of arguments.
 132 It reads the kernel to be loaded from the file referred to by the descriptor
 133 .IR kernel_fd ,
 134 and the initrd to be loaded from file referred to by the descriptor
 135 .IR initrd_fd .
 136 It also takes the length of the kernel command line in
 137 .IR cmdline_len
 138 and a pointer to the command line in
 139 .IR cmdline .
 140
 141 The
 142 .IR flags
 143 argument is a bit mask which modifies the behavior of the call.
 144 The following values can be specified in
 145 .IR flags :
 146 .TP
 147 .BR KEXEC_FILE_UNLOAD
 148 Unload the currently loaded kernel.
 149 .TP
 150 .BR KEXEC_FILE_ON_CRASH
 151 Load the new kernel in the memory region reserved for the crash kernel.
 152 This kernel is booted if the currently running kernel crashes.
 153 .TP
 154 .BR KEXEC_FILE_NO_INITRAMFS
 155 Loading initrd/initramfs is optional.
 156 Specify this flag if no initramfs is being loaded.
 157 If this flag is set, the value passed in
 158 .IR initrd_fd
 159 is ignored.
 160 .SH RETURN VALUE
 161 On success, these system calls returns 0.
 162 On error, \-1 is returned and
 163 .I errno
 164 is set to indicate the error.
 165 .SH ERRORS
 166 .TP
 167 .B EBUSY
 168 Another crash kernel is already being loaded
 169 or a crash kernel is already in use.
 170 .TP
 171 .B EINVAL
 172 .I flags
 173 is invalid; or
 174 .IR nr_segments
 175 is too large
 176 .\" KEXEC_SEGMENT_MAX == 16
 177 .TP
 178 .B ENOEXEC
 179 .I kernel_fd
 180 does not refer to an open file, or the kernel can't load this file.
 181 .TP
 182 .B EPERM
 183 The caller does not have the
 184 .BR CAP_SYS_BOOT
 185 capability.
 186 .SH VERSIONS
 187 The
 188 .BR kexec_load ()
 189 system call first appeared in Linux 2.6.13.
 190 .SH CONFORMING TO
 191 This system call is Linux-specific.
 192 .SH NOTES
 193 Currently, there is no glibc support for these system calls.
 194 Call them using
 195 .BR syscall (2).
 196 .PP
 197 The required constants are in the Linux kernel source file
 198 .IR linux/kexec.h ,
 199 which is not currently exported to glibc.
 200 .\" FIXME . Andi submitted a patch for this.
 201 .\" Check if it got accepted later.
 202 Therefore, these constants must be defined manually.
 203
 204 This system call is available only if the kernel was configured with
 205 .BR CONFIG_KEXEC .
 206 .SH SEE ALSO
 207 .BR reboot (2),
 208 .BR syscall (2)