[RFC PATCH] Add support for grub-emu to kexec Linux menu entries

[Javier Martinez Canillas]

From: John Jolly <address@hidden>

The GRUB emulator is used as a debugging utility but it could also be used
as a user-space bootloader if there is support to boot an operating system.

The Linux kernel is already able to (re)boot another kernel via the kexec
boot mechanism. So the grub-emu tool could rely on this feature and have
linux and initrd commands that are used to pass a kernel, initramfs image
and command line parameters to kexec for booting a selected menu entry.

By default the systemctl kexec option is used so systemd can shutdown all
of the running services before doing a reboot using kexec. But if this is
not present, it fallbacks to executing the kexec user-space tool directly.

Signed-off-by: John Jolly <address@hidden>
Signed-off-by: Javier Martinez Canillas <address@hidden>


---
Hello,

This patch has been in the SUSE grub2 package for some time and we have also
included in the Fedora grub2 package now. I'm posting it as an RFC because I
think that will need some discussions before being able to merge this patch.

Best regards,
Javier

 grub-core/Makefile.am        |   1 +
 grub-core/Makefile.core.def  |   2 +-
 grub-core/kern/emu/main.c    |   4 +
 grub-core/kern/emu/misc.c    |  18 +++-
 grub-core/loader/emu/linux.c | 182 +++++++++++++++++++++++++++++++++++
 include/grub/emu/exec.h      |   4 +-
 include/grub/emu/hostfile.h  |   3 +-
 include/grub/emu/misc.h      |   3 +
 8 files changed, 213 insertions(+), 4 deletions(-)
 create mode 100644 grub-core/loader/emu/linux.c

diff --git a/grub-core/Makefile.am b/grub-core/Makefile.am
index 3ea8e7ff45f..ede59617078 100644
--- a/grub-core/Makefile.am
+++ b/grub-core/Makefile.am
@@ -303,6 +303,7 @@ KERNEL_HEADER_FILES += $(top_srcdir)/include/grub/emu/net.h
 KERNEL_HEADER_FILES += $(top_srcdir)/include/grub/emu/hostdisk.h
 KERNEL_HEADER_FILES += $(top_srcdir)/include/grub/emu/hostfile.h
 KERNEL_HEADER_FILES += $(top_srcdir)/include/grub/extcmd.h
+KERNEL_HEADER_FILES += $(top_srcdir)/include/grub/emu/exec.h
 if COND_GRUB_EMU_SDL
 KERNEL_HEADER_FILES += $(top_srcdir)/include/grub/sdl.h
 endif
diff --git a/grub-core/Makefile.core.def b/grub-core/Makefile.core.def
index 26937041756..670b1cc01ff 100644
--- a/grub-core/Makefile.core.def
+++ b/grub-core/Makefile.core.def
@@ -1801,9 +1801,9 @@ module = {
   arm64 = loader/arm64/linux.c;
   riscv32 = loader/riscv/linux.c;
   riscv64 = loader/riscv/linux.c;
+  emu = loader/emu/linux.c;
   common = loader/linux.c;
   common = lib/cmdline.c;
-  enable = noemu;
 };
 
 module = {
diff --git a/grub-core/kern/emu/main.c b/grub-core/kern/emu/main.c
index 425bb960347..27edcfc9aee 100644
--- a/grub-core/kern/emu/main.c
+++ b/grub-core/kern/emu/main.c
@@ -107,6 +107,7 @@ static struct argp_option options[] = {
    N_("use GRUB files in the directory DIR [default=%s]"), 0},
   {"verbose",     'v', 0,      0, N_("print verbose messages."), 0},
   {"hold",     'H', N_("SECS"),      OPTION_ARG_OPTIONAL, N_("wait until a 
debugger will attach"), 0},
+  {"kexec",       'X', 0,      0, N_("use kexec to boot Linux kernels."), 0},
   { 0, 0, 0, 0, 0, 0 }
 };
 
@@ -164,6 +165,9 @@ argp_parser (int key, char *arg, struct argp_state *state)
     case 'v':
       verbosity++;
       break;
+    case 'X':
+      grub_util_set_kexecute ();
+      break;
 
     case ARGP_KEY_ARG:
       {
diff --git a/grub-core/kern/emu/misc.c b/grub-core/kern/emu/misc.c
index 65db79baa10..754d0cda02f 100644
--- a/grub-core/kern/emu/misc.c
+++ b/grub-core/kern/emu/misc.c
@@ -39,6 +39,7 @@
 #include <grub/emu/misc.h>
 
 int verbosity;
+int kexecute;
 
 void
 grub_util_warn (const char *fmt, ...)
@@ -82,7 +83,7 @@ grub_util_error (const char *fmt, ...)
   vfprintf (stderr, fmt, ap);
   va_end (ap);
   fprintf (stderr, ".\n");
-  exit (1);
+  grub_exit ();
 }
 
 void *
@@ -141,6 +142,9 @@ xasprintf (const char *fmt, ...)
 void
 grub_exit (void)
 {
+#if defined (GRUB_KERNEL)
+  grub_reboot ();
+#endif
   exit (1);
 }
 #endif
@@ -202,3 +206,15 @@ grub_util_load_image (const char *path, char *buf)
 
   fclose (fp);
 }
+
+void
+grub_util_set_kexecute (void)
+{
+  kexecute++;
+}
+
+int
+grub_util_get_kexecute (void)
+{
+  return kexecute;
+}
diff --git a/grub-core/loader/emu/linux.c b/grub-core/loader/emu/linux.c
new file mode 100644
index 00000000000..020cf56cd19
--- /dev/null
+++ b/grub-core/loader/emu/linux.c
@@ -0,0 +1,182 @@
+/*
+ *  GRUB  --  GRand Unified Bootloader
+ *  Copyright (C) 2006,2007,2008,2009,2010  Free Software Foundation, Inc.
+ *
+ *  GRUB is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  GRUB is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty 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 GRUB.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <grub/loader.h>
+#include <grub/dl.h>
+#include <grub/command.h>
+#include <grub/time.h>
+
+#include <grub/emu/exec.h>
+#include <grub/emu/hostfile.h>
+#include <grub/emu/misc.h>
+
+GRUB_MOD_LICENSE ("GPLv3+");
+
+static grub_dl_t my_mod;
+
+static char *kernel_path;
+static char *initrd_path;
+static char *boot_cmdline;
+
+static grub_err_t
+grub_linux_boot (void)
+{
+  grub_err_t rc = GRUB_ERR_NONE;
+  char *initrd_param;
+  const char *kexec[] = { "kexec", "-l", kernel_path, boot_cmdline, NULL, NULL 
};
+  const char *systemctl[] = { "systemctl", "kexec", NULL };
+  int kexecute = grub_util_get_kexecute ();
+
+  if (initrd_path)
+    {
+      initrd_param = grub_xasprintf ("--initrd=%s", initrd_path);
+      kexec[3] = initrd_param;
+      kexec[4] = boot_cmdline;
+    }
+  else
+    {
+      initrd_param = grub_xasprintf ("%s", "");
+    }
+
+  grub_dprintf ("linux", "%serforming 'kexec -l %s %s %s'\n",
+                (kexecute) ? "P" : "Not p",
+                kernel_path, initrd_param, boot_cmdline);
+
+  if (kexecute)
+    rc = grub_util_exec (kexec);
+
+  grub_free(initrd_param);
+
+  if (rc != GRUB_ERR_NONE)
+    {
+      grub_error (rc, N_("Error trying to perform kexec load operation."));
+      grub_sleep (3);
+      return rc;
+    }
+
+  if (kexecute < 1)
+    grub_fatal (N_("Use '"PACKAGE"-emu --kexec' to force a system restart."));
+
+  grub_dprintf ("linux", "Performing 'systemctl kexec' (%s) ",
+               (kexecute==1) ? "do-or-die" : "just-in-case");
+  rc = grub_util_exec (systemctl);
+
+  if (rc == GRUB_ERR_NONE)
+    return rc;
+
+  grub_error (rc, N_("Error trying to perform 'systemctl kexec'"));
+
+  /* need to check read-only root before resetting hard!? */
+  grub_dprintf ("linux", "Performing 'kexec -e -x'");
+  kexec[1] = "-e";
+  kexec[2] = "-x";
+  kexec[3] = NULL;
+  rc = grub_util_exec (kexec);
+  if ( rc != GRUB_ERR_NONE )
+    grub_fatal (N_("Error trying to directly perform 'kexec -e'."));
+
+  return rc;
+}
+
+static grub_err_t
+grub_linux_unload (void)
+{
+  grub_dl_unref (my_mod);
+  if ( boot_cmdline != NULL )
+    grub_free (boot_cmdline);
+  boot_cmdline = NULL;
+  return GRUB_ERR_NONE;
+}
+
+static grub_err_t
+grub_cmd_linux (grub_command_t cmd __attribute__ ((unused)), int argc, char 
*argv[])
+{
+  int i;
+  char *tempstr;
+
+  grub_dl_ref (my_mod);
+
+  if (argc == 0)
+    return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("filename expected"));
+
+  if ( !grub_util_is_regular (argv[0]) )
+    return grub_error (GRUB_ERR_FILE_NOT_FOUND, N_("Cannot find kernel file 
%s"), argv[0]);
+
+  if ( kernel_path != NULL )
+    grub_free (kernel_path);
+
+  kernel_path = grub_xasprintf ("%s", argv[0]);
+
+  if ( boot_cmdline != NULL )
+    {
+      grub_free(boot_cmdline);
+      boot_cmdline = NULL;
+    }
+
+  if ( argc > 1 )
+    {
+      boot_cmdline = grub_xasprintf("--command-line=%s", argv[1]);
+      for ( i = 2; i < argc; i++ )
+        {
+          tempstr = grub_xasprintf("%s %s", boot_cmdline, argv[i]);
+          grub_free(boot_cmdline);
+          boot_cmdline = tempstr;
+        }
+    }
+
+  grub_loader_set (grub_linux_boot, grub_linux_unload, 0);
+
+  return GRUB_ERR_NONE;
+}
+
+static grub_err_t
+grub_cmd_initrd (grub_command_t cmd __attribute__ ((unused)), int argc, char 
*argv[])
+{
+  if (argc == 0)
+    return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("filename expected"));
+
+  if ( !grub_util_is_regular (argv[0]) )
+    return grub_error (GRUB_ERR_FILE_NOT_FOUND, N_("Cannot find initrd file 
%s"), argv[0]);
+
+  if ( initrd_path != NULL )
+    grub_free (initrd_path);
+
+  initrd_path = grub_xasprintf("%s", argv[0]);
+
+  grub_dl_unref (my_mod);
+
+  return GRUB_ERR_NONE;
+}
+
+static grub_command_t cmd_linux, cmd_initrd;
+
+GRUB_MOD_INIT (linux)
+{
+  cmd_linux = grub_register_command ("linux", grub_cmd_linux, 0, N_("Load 
Linux."));
+  cmd_initrd = grub_register_command ("initrd", grub_cmd_initrd, 0, N_("Load 
initrd."));
+  my_mod = mod;
+  kernel_path = NULL;
+  initrd_path = NULL;
+  boot_cmdline = NULL;
+}
+
+GRUB_MOD_FINI (linux)
+{
+  grub_unregister_command (cmd_linux);
+  grub_unregister_command (cmd_initrd);
+}
diff --git a/include/grub/emu/exec.h b/include/grub/emu/exec.h
index d1073ef86af..1b61b4a2e5d 100644
--- a/include/grub/emu/exec.h
+++ b/include/grub/emu/exec.h
@@ -23,6 +23,8 @@
 #include <stdarg.h>
 
 #include <sys/types.h>
+#include <grub/symbol.h>
+
 pid_t
 grub_util_exec_pipe (const char *const *argv, int *fd);
 pid_t
@@ -32,7 +34,7 @@ int
 grub_util_exec_redirect_all (const char *const *argv, const char *stdin_file,
                             const char *stdout_file, const char *stderr_file);
 int
-grub_util_exec (const char *const *argv);
+EXPORT_FUNC(grub_util_exec) (const char *const *argv);
 int
 grub_util_exec_redirect (const char *const *argv, const char *stdin_file,
                         const char *stdout_file);
diff --git a/include/grub/emu/hostfile.h b/include/grub/emu/hostfile.h
index cfb1e2b5661..a61568e36e9 100644
--- a/include/grub/emu/hostfile.h
+++ b/include/grub/emu/hostfile.h
@@ -22,6 +22,7 @@
 #include <grub/disk.h>
 #include <grub/partition.h>
 #include <sys/types.h>
+#include <grub/symbol.h>
 #include <grub/osdep/hostfile.h>
 
 int
@@ -29,7 +30,7 @@ grub_util_is_directory (const char *path);
 int
 grub_util_is_special_file (const char *path);
 int
-grub_util_is_regular (const char *path);
+EXPORT_FUNC(grub_util_is_regular) (const char *path);
 
 char *
 grub_util_path_concat (size_t n, ...);
diff --git a/include/grub/emu/misc.h b/include/grub/emu/misc.h
index ce464cfd007..5ef4f79e689 100644
--- a/include/grub/emu/misc.h
+++ b/include/grub/emu/misc.h
@@ -56,6 +56,9 @@ void EXPORT_FUNC(grub_util_warn) (const char *fmt, ...) 
__attribute__ ((format (
 void EXPORT_FUNC(grub_util_info) (const char *fmt, ...) __attribute__ ((format 
(GNU_PRINTF, 1, 2)));
 void EXPORT_FUNC(grub_util_error) (const char *fmt, ...) __attribute__ 
((format (GNU_PRINTF, 1, 2), noreturn));
 
+void EXPORT_FUNC(grub_util_set_kexecute) (void);
+int EXPORT_FUNC(grub_util_get_kexecute) (void) WARN_UNUSED_RESULT;
+
 grub_uint64_t EXPORT_FUNC (grub_util_get_cpu_time_ms) (void);
 
 #ifdef HAVE_DEVICE_MAPPER
-- 
2.21.0