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

[joeyli]

Hi Baoquan, 

Thanks for your response!

On Thu, Jul 14, 2016 at 05:51:24PM +0800, Baoquan He wrote:
> On 07/14/16 at 04:45pm, 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.
> > 
> > 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.
> 
> Usually distribuition system uses script to build a framework to
> connect the kexec/kdump, makedumpfile utility chain. This can make user
> execute a very simple script command to implement kexec load or kexec
> jumping job. In this case script can do what you are trying to do.
> 

Yes, the fallback function can be implemented by script. But a new kexec
option is useful to the distro that it may not provides help scripts to
user.

> Besides, have you actually met that kexec-file failed but old kexec
> syscall works? I mean how did you test it? I am wondering when it will
> happen.
> 
> Thanks
> Baoquan
>

The currently mainline kernel allows to set CONFIG_KEXEC or CONFIG_KEXEC_FILE
individual. So if kexec found that the file based kexec syscall isn't
available then this is a case to fallback to old kexec.

Another case is when KEXEC_VERIFY_SIG is set, The fallback function is more
convenient to user to build his own kernel for using or testing. The kexec
tool can try old syscall when verification failed.


Thanks a lot!
Joey Lee
 
> > 
> > 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
> > 
> > 
> > _______________________________________________
> > kexec mailing list
> > kexec at lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/kexec