Add setup_kexec method to prepare the system for a reboot with kexec

This allows the system to be rebooted faster after the installation is
complete by skipping the BIOS/Firmware and bootloader. It uses the new
kernel, initrd and kernel cmdline arguments from the newly installed
system so a kexec reboot should be indistinguishable from a cold boot.

pyanaconda/kexec.py

@@ -0,0 +1,110 @@
+# kexec.py
+#
+# Setup kexec to restart the system using the default bootloader entry
+#
+# Copyright (C) 2015 Red Hat, Inc.
+#
+# This copyrighted material is made available to anyone wishing to use,
+# modify, copy, or redistribute it subject to the terms and conditions of
+# the GNU General Public License v.2, or (at your option) any later version.
+# This program is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY expressed or implied, including the implied warranties of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General
+# Public License for more details.  You should have received a copy of the
+# GNU General Public License along with this program; if not, write to the
+# Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+# 02110-1301, USA.  Any Red Hat trademarks that are incorporated in the
+# source code or documentation are not subject to the GNU General Public
+# License and may only be used or replicated with the express permission of
+# Red Hat, Inc.
+#
+# Red Hat Author(s): Brian C. Lane <[email protected]>
+#
+import shutil
+from collections import namedtuple
+
+from pyanaconda.iutil import getSysroot, execReadlines, execWithRedirect
+from pyanaconda.simpleconfig import unquote
+
+import logging
+log = logging.getLogger("anaconda")
+
+class GrubbyInfoError(Exception):
+    pass
+
+def run_grubby(args=None):
+    """ Run grubby and retrieve the kernel, initrd and boot arguments
+
+        :param list args: Arguments to pass to grubby.
+        :returns: kernel path, initrd path, root device, kernel cmdline args.
+        :rtype: namedtuple
+        :raises: some error on failure
+
+        The returned namedtuple contains the following attributes:
+            kernel, initrd, root, args
+    """
+    attrs = ["kernel", "initrd", "root", "args"]
+    boot_info = namedtuple("boot_info", attrs)
+
+    if not args:
+        args = ["--info", "DEFAULT"]
+
+    # Run grubby and fill in the boot_info with the first values seen, exit the
+    # loop when all of the needed values have been gathered.
+    try:
+
+        for line in execReadlines("grubby", args, root=getSysroot()):
+            key, _sep, value = line.partition("=")
+            value = unquote(value)
+            if key in attrs:
+                setattr(boot_info, key, value)
+                attrs.remove(key)
+            if not attrs:
+                break
+    except OSError as e:
+        log.error("run_grubby failed: %s", e)
+        raise GrubbyInfoError(e)
+
+    if len(attrs) > 0:
+        raise GrubbyInfoError("Missing values: %s" % ", ".join(attrs))
+
+    log.info("grubby boot info for (%s): %s", args, boot_info)
+    return boot_info
+
+
+def setup_kexec(extra_args=None):
+    """ Setup kexec to use the new kernel and default bootloader entry
+
+        :param list extra_args: Extra arguments to pass to kexec
+
+        This uses grubby to determine the bootloader arguments from the default entry,
+        and then sets up kexec so that reboot will use the new kernel and initrd instead
+        of doing a full reboot.
+
+        .. note::
+            Once kexec is called there is nothing else to do, the reboot code already handles
+            having kexec setup.
+    """
+    try:
+        boot_info = run_grubby()
+    except GrubbyInfoError:
+        # grubby couldn't find a default entry, use the first one instead
+        try:
+            boot_info = run_grubby(["--info", "ALL"])
+        except GrubbyInfoError:
+            # Grubby can't get the bootloader's info, kexec won't work.
+            log.error("kexec reboot setup failed, grubby could not get bootloader info.")
+            return
+
+    # Copy the kernel and initrd to /tmp/
+    shutil.copy2(getSysroot()+boot_info.kernel, "/tmp/vmlinuz-kexec-reboot")
+    shutil.copy2(getSysroot()+boot_info.initrd, "/tmp/initrd-kexec-reboot")
+
+    append = "root=%s %s" % (boot_info.root, boot_info.args)
+    args = ["--initrd", "/tmp/initrd-kexec-reboot", "--append", append, "-l", "/tmp/vmlinuz-kexec-reboot"]
+    try:
+        rc = execWithRedirect("kexec", args)
+    except OSError as e:
+        log.error("setup_kexec failed: %s", e)
+    if rc != 0:
+        log.error("setup_kexec failed with rc=%d: See program.log for output", rc)