kexec_file_load

KEXEC_LOAD(2)               Linux Programmer's Manual              KEXEC_LOAD(2)



NAME
       kexec_load, kexec_file_load - load a new kernel for later execution

SYNOPSIS
       #include <linux/kexec.h>

       long kexec_load(unsigned long entry, unsigned long nr_segments,
                       struct kexec_segment *segments, unsigned long flags);

       long kexec_file_load(int kernel_fd, int initrd_fd,
                           unsigned long cmdline_len, const char *cmdline,
                           unsigned long flags);

       Note: There are no glibc wrappers for these system calls; see NOTES.

DESCRIPTION
       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.

   kexec_file_load()
       The kexec_file_load() system call is similar to kexec_load(), but it
       takes a different set of arguments.  It reads the kernel to be loaded
       from the file referred to by the file descriptor kernel_fd, and the
       initrd (initial RAM disk) to be loaded from file referred to by the file
       descriptor initrd_fd.  The cmdline argument is a pointer to a buffer
       containing the command line for the new kernel.  The cmdline_len argument
       specifies size of the buffer.  The last byte in the buffer must be a null
       byte ('\0').

       The flags argument is a bit mask which modifies the behavior of the call.
       The following values can be specified in flags:

       KEXEC_FILE_UNLOAD
              Unload the currently loaded kernel.

       KEXEC_FILE_ON_CRASH
              Load the new kernel in the memory region reserved for the crash
              kernel (as for KEXEC_ON_CRASH).  This kernel is booted if the
              currently running kernel crashes.

       KEXEC_FILE_NO_INITRAMFS
              Loading initrd/initramfs is optional.  Specify this flag if no
              initramfs is being loaded.  If this flag is set, the value passed
              in initrd_fd is ignored.

       The kexec_file_load() system call was added to provide support for
       systems where "kexec" loading should be restricted to only kernels that
       are signed.  This system call is available only if the kernel was
       configured with CONFIG_KEXEC_FILE.

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

ERRORS
       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.

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

CONFORMING TO
       These system calls are Linux-specific.

NOTES
       Currently, there is no glibc support for these system calls.  Call them
       using syscall(2).

SEE ALSO
       reboot(2), syscall(2), kexec(8)

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

COLOPHON
       This page is part of release 5.10 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.




Linux                              2019-03-06                      KEXEC_LOAD(2)