Manpages - kexec_load.2

kexec_load, kexec_file_load - load a new kernel for later execution

  #include <linux/kexec.h> /* Definition of KEXEC_* constants */
  #include <sys/syscall.h> /* Definition of SYS_* constants */
  #include <unistd.h>

  long syscall(SYS_kexec_load, unsigned long entry,
   unsigned long nr_segments",structkexec_segment*"segments,
   unsigned long flags);
  long syscall(SYS_kexec_file_load, int kernel_fd, int initrd_fd,
   unsigned long cmdline_len, const char *cmdline,
   unsigned long flags);

Note: glibc provides no wrappers for these system calls, necessitating the use of *syscall*(2).

The *kexec_load*() system call loads a new kernel that can be executed later by *reboot*(2).

The flags argument is a bit mask that controls the operation of the call. The following values can be specified in flags:

KEXEC_ON_CRASH (since Linux 2.6.13)

Execute the new kernel automatically on a system crash. This “crash kernel” is loaded into an area of reserved memory that is determined at boot time using the crashkernel kernel command-line parameter. The location of this reserved memory is exported to user space via the /proc/iomem file, in an entry labeled “Crash kernel”. A user-space application can parse this file and prepare a list of segments (see below) that specify this reserved memory as destination. If this flag is specified, the kernel checks that the target segments specified in segments fall within the reserved region.

KEXEC_PRESERVE_CONTEXT (since Linux 2.6.27)

Preserve the system hardware and software states before executing the new kernel. This could be used for system suspend. This flag is available only if the kernel was configured with CONFIG_KEXEC_JUMP, and is effective only if nr_segments is greater than 0.

The high-order bits (corresponding to the mask 0xffff0000) of flags contain the architecture of the to-be-executed kernel. Specify (OR) the constant KEXEC_ARCH_DEFAULT to use the current architecture, or one of the following architecture constants KEXEC_ARCH_386, KEXEC_ARCH_68K, KEXEC_ARCH_X86_64, KEXEC_ARCH_PPC, KEXEC_ARCH_PPC64, KEXEC_ARCH_IA_64, KEXEC_ARCH_ARM, KEXEC_ARCH_S390, KEXEC_ARCH_SH, KEXEC_ARCH_MIPS, and KEXEC_ARCH_MIPS_LE. The architecture must be executable on the CPU of the system.

The entry argument is the physical entry address in the kernel image. The nr_segments argument is the number of segments pointed to by the segments pointer; the kernel imposes an (arbitrary) limit of 16 on the number of segments. The segments argument is an array of kexec_segment structures which define the kernel layout:

  struct kexec_segment {
      void   *buf;        /* Buffer in user space */
      size_t  bufsz;      /* Buffer length in user space */
      void   *mem;        /* Physical address of kernel */
      size_t  memsz;      /* Physical address length */
  };

The kernel image defined by segments is copied from the calling process into the kernel either in regular memory or in reserved memory (if KEXEC_ON_CRASH is set). The kernel first performs various sanity checks on the information passed in segments. If these checks pass, the kernel copies the segment data to kernel memory. Each segment specified in segments is copied as follows:

• buf and bufsz identify a memory region in the caller’s virtual address space that is the source of the copy. The value in bufsz may not exceed the value in the memsz field.
• mem and memsz specify a physical address range that is the target of the copy. The values specified in both fields must be multiples of the system page size.
• bufsz bytes are copied from the source buffer to the target kernel buffer. If bufsz is less than memsz, then the excess bytes in the kernel buffer are zeroed out.

In case of a normal kexec (i.e., the KEXEC_ON_CRASH flag is not set), the segment data is loaded in any available memory and is moved to the final destination at kexec reboot time (e.g., when the *kexec*(8) command is executed with the -e option).

In case of kexec on panic (i.e., the KEXEC_ON_CRASH flag is set), the segment data is loaded to reserved memory at the time of the call, and, after a crash, the kexec mechanism simply passes control to that kernel.

The kexec_load*() system call is available only if the kernel was configured with *CONFIG_KEXEC.

On success, these system calls returns 0. On error, -1 is returned and errno is set to indicate the error.

EADDRNOTAVAIL

The KEXEC_ON_CRASH flags was specified, but the region specified by the mem and memsz fields of one of the segments entries lies outside the range of memory reserved for the crash kernel.

EADDRNOTAVAIL

The value in a mem or memsz field in one of the segments entries is not a multiple of the system page size.

EBADF

kernel_fd or initrd_fd is not a valid file descriptor.

EBUSY

Another crash kernel is already being loaded or a crash kernel is already in use.

EINVAL

flags is invalid.

EINVAL

The value of a bufsz field in one of the segments entries exceeds the value in the corresponding memsz field.

EINVAL

nr_segments exceeds KEXEC_SEGMENT_MAX (16).

EINVAL

Two or more of the kernel target buffers overlap.

EINVAL

The value in cmdline[cmdline_len-1] is not ’\0’.

EINVAL

The file referred to by kernel_fd or initrd_fd is empty (length zero).

ENOEXEC

kernel_fd does not refer to an open file, or the kernel can’t load this file. Currently, the file must be a bzImage and contain an x86 kernel that is loadable above 4 GiB in memory (see the kernel source file Documentation/x86/boot.txt).

ENOMEM

Could not allocate memory.

EPERM

The caller does not have the CAP_SYS_BOOT capability.

The *kexec_load*() system call first appeared in Linux 2.6.13. The *kexec_file_load*() system call first appeared in Linux 3.17.

These system calls are Linux-specific.

*reboot*(2), *syscall*(2), *kexec*(8)

The kernel source files Documentation/kdump/kdump.txt and Documentation/admin-guide/kernel-parameters.txt

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