unix: add KexecFileLoad on linux/{amd64,ppc64x,s390x}

Add a wrapper for the kexec_file_load syscall on the architectures that
implement it (amd64, ppc64x, s390x). See
http://man7.org/linux/man-pages/man2/kexec_file_load.2.html

Change-Id: Ie29f871902176610a6ba7ed0a7bcc95c10eb172b
Reviewed-on: https://go-review.googlesource.com/c/140037
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

unix/mkerrors.sh

@@ -193,6 +193,7 @@ struct ltchars {
 #include <linux/falloc.h>
 #include <linux/filter.h>
 #include <linux/fs.h>
+#include <linux/kexec.h>
 #include <linux/keyctl.h>
 #include <linux/magic.h>
 #include <linux/memfd.h>
@@ -445,6 +446,7 @@ ccflags="$@"
 		$2 ~ /^(MS|MNT|UMOUNT)_/ ||
 		$2 ~ /^TUN(SET|GET|ATTACH|DETACH)/ ||
 		$2 ~ /^(O|F|E?FD|NAME|S|PTRACE|PT)_/ ||
+		$2 ~ /^KEXEC_/ ||
 		$2 ~ /^LINUX_REBOOT_CMD_/ ||
 		$2 ~ /^LINUX_REBOOT_MAGIC[12]$/ ||
 		$2 !~ "NLA_TYPE_MASK" &&

unix/syscall_linux_amd64.go

@@ -160,3 +160,16 @@ func Poll(fds []PollFd, timeout int) (n int, err error) {
 	}
 	return poll(&fds[0], len(fds), timeout)
 }
+
+//sys	kexecFileLoad(kernelFd int, initrdFd int, cmdlineLen int, cmdline string, flags int) (err error)
+
+func KexecFileLoad(kernelFd int, initrdFd int, cmdline string, flags int) error {
+	cmdlineLen := len(cmdline)
+	if cmdlineLen > 0 {
+		// Account for the additional NULL byte added by
+		// BytePtrFromString in kexecFileLoad. The kexec_file_load
+		// syscall expects a NULL-terminated string.
+		cmdlineLen++
+	}
+	return kexecFileLoad(kernelFd, initrdFd, cmdlineLen, cmdline, flags)
+}

unix/syscall_linux_ppc64x.go

@@ -136,3 +136,16 @@ func SyncFileRange(fd int, off int64, n int64, flags int) error {
 	// order of their arguments.
 	return syncFileRange2(fd, flags, off, n)
 }
+
+//sys	kexecFileLoad(kernelFd int, initrdFd int, cmdlineLen int, cmdline string, flags int) (err error)
+
+func KexecFileLoad(kernelFd int, initrdFd int, cmdline string, flags int) error {
+	cmdlineLen := len(cmdline)
+	if cmdlineLen > 0 {
+		// Account for the additional NULL byte added by
+		// BytePtrFromString in kexecFileLoad. The kexec_file_load
+		// syscall expects a NULL-terminated string.
+		cmdlineLen++
+	}
+	return kexecFileLoad(kernelFd, initrdFd, cmdlineLen, cmdline, flags)
+}

unix/syscall_linux_s390x.go

@@ -322,3 +322,16 @@ func Poll(fds []PollFd, timeout int) (n int, err error) {
 	}
 	return poll(&fds[0], len(fds), timeout)
 }
+
+//sys	kexecFileLoad(kernelFd int, initrdFd int, cmdlineLen int, cmdline string, flags int) (err error)
+
+func KexecFileLoad(kernelFd int, initrdFd int, cmdline string, flags int) error {
+	cmdlineLen := len(cmdline)
+	if cmdlineLen > 0 {
+		// Account for the additional NULL byte added by
+		// BytePtrFromString in kexecFileLoad. The kexec_file_load
+		// syscall expects a NULL-terminated string.
+		cmdlineLen++
+	}
+	return kexecFileLoad(kernelFd, initrdFd, cmdlineLen, cmdline, flags)
+}