man2/kexec_load.2

   1 .\" Copyright (C) 2010 Intel Corporation
   2 .\" Author: Andi Kleen
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  25 .\"
  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 .nf
  31 .B #include <linux/kexec.h>
  32
  33 .BI "long kexec_load(unsigned long " entry ", unsigned long " nr_segments ","
  34 .BI "                struct kexec_segment *" segments \
  35 ", unsigned long " flags ");"
  36
  37 .\" FIXME(kexec_file_load):
  38 .\"     Why are the return types of kexec_laod() and kexec_file_load()
  39 .\"     different?
  40 .BI "int kexec_file_load(int " kernel_fd ", int " initrd_fd ","
  41 .br
  42 .BI "                    unsigned long " cmdline_len  \
  43 ", const char *" cmdline ","
  44 .BI "                    unsigned long " flags ");"
  45
  46 .fi
  47 .IR Note :
  48 There are no glibc wrappers for these system calls; see NOTES.
  49 .SH DESCRIPTION
  50 The
  51 .BR kexec_load ()
  52 system call loads a new kernel that can be executed later by
  53 .BR reboot (2).
  54 .PP
  55 The
  56 .I flags
  57 argument is a bit mask that controls the operation of the call.
  58 The following values can be specified in
  59 .IR flags :
  60 .TP
  61 .BR KEXEC_ON_CRASH " (since Linux 2.6.13)"
  62 Execute the new kernel automatically on a system crash.
  63 .\" FIXME Explain in more detail how KEXEC_ON_CRASH is actually used
  64 .TP
  65 .BR KEXEC_PRESERVE_CONTEXT " (since Linux 2.6.27)"
  66 Preserve the system hardware and
  67 software states before executing the new kernel.
  68 This could be used for system suspend.
  69 This flag is available only if the kernel was configured with
  70 .BR CONFIG_KEXEC_JUMP ,
  71 and is effective only if
  72 .I nr_segments
  73 is greater than 0.
  74 .PP
  75 The high-order bits (corresponding to the mask 0xffff0000) of
  76 .I flags
  77 contain the architecture of the to-be-executed kernel.
  78 Specify (OR) the constant
  79 .B KEXEC_ARCH_DEFAULT
  80 to use the current architecture,
  81 or one of the following architecture constants
  82 .BR KEXEC_ARCH_386 ,
  83 .BR KEXEC_ARCH_68K ,
  84 .BR KEXEC_ARCH_X86_64 ,
  85 .BR KEXEC_ARCH_PPC ,
  86 .BR KEXEC_ARCH_PPC64 ,
  87 .BR KEXEC_ARCH_IA_64 ,
  88 .BR KEXEC_ARCH_ARM ,
  89 .BR KEXEC_ARCH_S390 ,
  90 .BR KEXEC_ARCH_SH ,
  91 .BR KEXEC_ARCH_MIPS ,
  92 and
  93 .BR KEXEC_ARCH_MIPS_LE .
  94 The architecture must be executable on the CPU of the system.
  95
  96 The
  97 .I entry
  98 argument is the physical entry address in the kernel image.
  99 The
 100 .I nr_segments
 101 argument is the number of segments pointed to by the
 102 .I segments
 103 pointer;
 104 the kernel imposes an (arbitrary) limit of 16 on the number of segments.
 105 The
 106 .I segments
 107 argument is an array of
 108 .I kexec_segment
 109 structures which define the kernel layout:
 110 .in +4n
 111 .nf
 112
 113 struct kexec_segment {
 114     void   *buf;        /* Buffer in user space */
 115     size_t  bufsz;      /* Buffer length in user space */
 116     void   *mem;        /* Physical address of kernel */
 117     size_t  memsz;      /* Physical address length */
 118 };
 119 .fi
 120 .in
 121 .PP
 122 .\" FIXME Explain the details of how the kernel image defined by segments
 123 .\" is copied from the calling process into previously reserved memory.
 124 The kernel image defined by
 125 .I segments
 126 is copied from the calling process into previously reserved memory.
 127 .SS kexec_file_load()
 128 The
 129 .BR kexec_file_load ()
 130 system call is similar to
 131 .BR kexec_load (),
 132 but it takes a different set of arguments.
 133 It reads the kernel to be loaded from the file referred to by the descriptor
 134 .IR kernel_fd ,
 135 and the initrd (initial RAM disk)
 136 to be loaded from file referred to by the descriptor
 137 .IR initrd_fd .
 138 The
 139 .IR cmdline
 140 argument is a pointer to a string containing the command line
 141 for the new kernel; the
 142 .IR cmdline_len
 143 argument specifies the length of the string in
 144 .IR cmdline .
 145
 146 The
 147 .IR flags
 148 argument is a bit mask which modifies the behavior of the call.
 149 The following values can be specified in
 150 .IR flags :
 151 .TP
 152 .BR KEXEC_FILE_UNLOAD
 153 Unload the currently loaded kernel.
 154 .TP
 155 .BR KEXEC_FILE_ON_CRASH
 156 Load the new kernel in the memory region reserved for the crash kernel.
 157 This kernel is booted if the currently running kernel crashes.
 158 .TP
 159 .BR KEXEC_FILE_NO_INITRAMFS
 160 Loading initrd/initramfs is optional.
 161 Specify this flag if no initramfs is being loaded.
 162 If this flag is set, the value passed in
 163 .IR initrd_fd
 164 is ignored.
 165 .SH RETURN VALUE
 166 On success, these system calls returns 0.
 167 On error, \-1 is returned and
 168 .I errno
 169 is set to indicate the error.
 170 .SH ERRORS
 171 .TP
 172 .B EBUSY
 173 Another crash kernel is already being loaded
 174 or a crash kernel is already in use.
 175 .TP
 176 .B EINVAL
 177 .I flags
 178 is invalid; or
 179 .IR nr_segments
 180 is too large
 181 .\" KEXEC_SEGMENT_MAX == 16
 182 .TP
 183 .B ENOEXEC
 184 .I kernel_fd
 185 does not refer to an open file, or the kernel can't load this file.
 186 .TP
 187 .B EPERM
 188 The caller does not have the
 189 .BR CAP_SYS_BOOT
 190 capability.
 191 .SH VERSIONS
 192 The
 193 .BR kexec_load ()
 194 system call first appeared in Linux 2.6.13.
 195 The
 196 .BR kexec_file_load ()
 197 system call first appeared in Linux 3.17.
 198 .SH CONFORMING TO
 199 These system calls are Linux-specific.
 200 .SH NOTES
 201 Currently, there is no glibc support for these system calls.
 202 Call them using
 203 .BR syscall (2).
 204 .PP
 205 The required constants are in the Linux kernel source file
 206 .IR linux/kexec.h ,
 207 which is not currently exported to glibc.
 208 Therefore, these constants must be defined manually.
 209
 210 .\" FIXME(kexec_file_load):
 211 .\" Is the following rationale accurate? Does it need expanding?
 212 The
 213 .BR kexec_file_load ()
 214 .\" See also http://lwn.net/Articles/603116/
 215 system call was added to provide support for systems
 216 where "kexec" loading should be restricted to
 217 only kernels that are signed.
 218
 219 The
 220 .BR kexec_load ()
 221 system call is available only if the kernel was configured with
 222 .BR CONFIG_KEXEC .
 223 The
 224 .BR kexec_file_load ()
 225 system call is available only if the kernel was configured with
 226 .BR CONFIG_KEXEC_FILE .
 227 .\" FIXME(kexec_file_load):
 228 .\"     Does kexec_file_load() need any other CONFIG_* options to be defined?
 229 .SH SEE ALSO
 230 .BR reboot (2),
 231 .BR syscall (2),
 232 .BR kexec (8)