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

[Vivek Goyal]

On Thu, Jul 14, 2016 at 04:45:11PM +0800, Lee, Chun-Yi wrote:
> 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.

I think caller should switch to using different interface if need be. But
I don't see much point in providing an option for this in kexec-tools.

Vivek

> 
> 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