[PATCH] kexec: Add option to fallback to old kexec syscall when kexec file based syscall failed

[Lee, Chun-Yi]

This patch adds a new "--fallback-kexec" option to give a chance to
fallback to old kexec syscall when file based kexec syscall operation
failed.

This option works with --kexec-file-syscall to provide more flexible
way to adapt to different kernels that those kernels built with
different kexec syscall config or have different verification policy.

Cc: Simon Horman <horms at verge.net.au>
Cc: Petr Tesarik <ptesarik at suse.com>
Cc: Vivek Goyal <vgoyal at redhat.com>
Signed-off-by: Lee, Chun-Yi <jlee at suse.com>
---
 kexec/kexec.c | 13 +++++++++++++
 kexec/kexec.h |  4 +++-
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/kexec/kexec.c b/kexec/kexec.c
index 500e5a9..e05b43f 100644
--- a/kexec/kexec.c
+++ b/kexec/kexec.c
@@ -969,6 +969,7 @@ void usage(void)
 	       "                      preserve context)\n"
 	       "                      to original kernel.\n"
 	       " -s, --kexec-file-syscall Use file based syscall for kexec operation\n"
+	       "     --fallback-kexec     Fallback to old kexec when file based syscall failed\n"
 	       " -d, --debug           Enable debugging to help spot a failure.\n"
 	       "\n"
 	       "Supported kernel file types and options: \n");
@@ -1204,6 +1205,7 @@ int main(int argc, char *argv[])
 	int do_unload = 0;
 	int do_reuse_initrd = 0;
 	int do_kexec_file_syscall = 0;
+	int do_fallback_kexec_syscall = 0;
 	void *entry = 0;
 	char *type = 0;
 	char *endptr;
@@ -1226,9 +1228,13 @@ int main(int argc, char *argv[])
 		case OPT_KEXEC_FILE_SYSCALL:
 			do_kexec_file_syscall = 1;
 			break;
+		case OPT_FALLBACK_KEXEC:
+			do_fallback_kexec_syscall = 1;
+			break;
 		}
 	}
 
+fallback:
 	/* Reset getopt for the next pass. */
 	opterr = 1;
 	optind = 1;
@@ -1407,6 +1413,13 @@ int main(int argc, char *argv[])
 			result = my_load(type, fileind, argc, argv,
 						kexec_flags, entry);
 	}
+	/* fallback to old kexec syscall */
+	if (do_kexec_file_syscall && result != 0 && do_fallback_kexec_syscall) {
+		fprintf(stderr, "Fallback to kexec syscall\n");
+		do_kexec_file_syscall = 0;
+		do_fallback_kexec_syscall = 0;
+		goto fallback;
+	}
 	/* Don't shutdown unless there is something to reboot to! */
 	if ((result == 0) && (do_shutdown || do_exec) && !kexec_loaded()) {
 		die("Nothing has been loaded!\n");
diff --git a/kexec/kexec.h b/kexec/kexec.h
index 9194f1c..65dbd56 100644
--- a/kexec/kexec.h
+++ b/kexec/kexec.h
@@ -225,7 +225,8 @@ extern int file_types;
 #define OPT_LOAD_PRESERVE_CONTEXT 259
 #define OPT_LOAD_JUMP_BACK_HELPER 260
 #define OPT_ENTRY		261
-#define OPT_MAX			262
+#define OPT_FALLBACK_KEXEC	262
+#define OPT_MAX			263
 #define KEXEC_OPTIONS \
 	{ "help",		0, 0, OPT_HELP }, \
 	{ "version",		0, 0, OPT_VERSION }, \
@@ -244,6 +245,7 @@ extern int file_types;
 	{ "mem-max",		1, 0, OPT_MEM_MAX }, \
 	{ "reuseinitrd",	0, 0, OPT_REUSE_INITRD }, \
 	{ "kexec-file-syscall",	0, 0, OPT_KEXEC_FILE_SYSCALL }, \
+	{ "fallback-kexec",     0, 0, OPT_FALLBACK_KEXEC }, \
 	{ "debug",		0, 0, OPT_DEBUG }, \
 
 #define KEXEC_OPT_STR "h?vdfxyluet:ps"
-- 
2.6.6