kexec_load.2: New page documenting kexec_load(2)

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/kexec_load.2

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+.TH KEXEC_LOAD 2 2010-06-16 "Linux" "Linux Programmer's Manual"
+.SH NAME
+kexec_load \- Load a new kernel for later execution.
+.SH SYNOPSIS
+.b #include <linux/kexec.h>
+.br
+.BI "long kexec_load(unsigned long " entry ", unsigned long " nr_segments ","
+.br
+.BI       "struct kexec_segment *" segments ", unsigned long " flags ");"
+.SH DESCRIPTION
+.BR kexec_load 
+loads a new kernel that can be executed later
+by 
+.I reboot(2).
+An alternative approach is to specify
+.B KEXEC_ON_CRASH
+in the 
+.I flags
+argument and then the new kernel will be automatically executed on a 
+system crash. 
+.\" XXX figure out how this is really used 
+With 
+.B KEXEC_PRESERVE_CONTEXT 
+specified in 
+.I flags
+kexec will preserve the system hard and 
+software state before executing the kexec kernel. This 
+could be used for system suspend.
+
+.I flags
+also contains the architecture of the executed kernel or
+be 
+.I KEXEC_ARCH_DEFAULT
+for the current architecture.
+Valid architectures are 
+.I KEXEC_ARCH_I386,
+.I KEXEC_ARCH_X86_64,
+.I KEXEC_ARCH_PPC,
+.I KEXEC_ARCH_PPC64,
+.I KEXEC_ARCH_IA_64,
+.I KEXEC_ARCH_ARM,
+.I KEXEC_ARCH_S390,
+.I KEXEC_ARCH_SH,
+.I KEXEC_ARCH_MIPS,
+.I KEXEC_ARCH_MIPS_LE.
+The architecture must be executable on the CPU of the system.
+
+.I entry 
+is the virtual entry address in the kernel image.
+.I nr_segments
+is the number of segments pointed to by the 
+.I segments
+pointer. 
+.I segments 
+is an array of 
+.I struct kexec_segment
+structures which define the kernel layout:
+.in +4n
+.nf
+
+struct kexec_segment {
+	void   *buf;	/* Buffer in user space */
+	size_t  bufsz;	/* Buffer length in user space */
+	void   *mem;	/* Virtual address of kernel */
+	size_t  memsz;	/* Virtual address length */
+};
+.fi
+.in
+.PP
+.\" XXX elaborate on this
+The kernel image defined by
+.I segments
+is copied from the calling process into previously reserved memory.
+.SH CONFORMING TO
+This system call is Linux-specific.
+.SH NOTES
+kexec_load is currently not defined in glibc. To call it use:
+.in +4n
+.nf
+#define _GNU_SOURCE
+#include <syscall.h>
+#include <asm/unistd.h>
+#include <linux/kexec.h>
+
+ret = syscall(__NR_kexec_load, entry, nr_segments, segments, flags);
+.fi
+.in
+.PP
+.I linux/kexec.h as a exported header is only available in 2.6.38
+and later kernels, in earlier kernels the constants need to be copied
+out of the kernel source.
+.SH SEE ALSO
+.BR syscall (2),
+.BR reboot (2)