Hi Petr,

On 02/23/18 at 09:29am, Petr Tesarik wrote:
> Hi Baoquan,
> 
> On Fri, 23 Feb 2018 07:20:43 +0800
> Baoquan He <b...@redhat.com> wrote:
> 
> > Hi Michal,
> > 
> > On 02/22/18 at 11:24pm, Michal Suchanek wrote:
> > > The new KEXEC_FILE_LOAD is preferred in the case the platform supports
> > > it because it allows kexec in locked down secure boot mode.
> > > 
> > > However, some platforms do not support it so fall back to the old
> > > syscall there.  
> > 
> > I didn't read code change, just from patch log, I tend to not agree. There
> > are two options KEXEC_FILE_LOAD and KEXEC_LOAD, some platforms do not
> > support, why does some platforms not choose KEXEC_LOAD, the working one?
> > Why bother to make change in code? I believe there's returned message
> > telling if KEXEC_FILE_LOAD works or not.
> 
> Well... let me give a bit of background. As you have probably noticed,
> this syscall was originally available only for x86_64, but more and
> more architectures are also adding it now.
> 
> Next, kexec is actually called by a script (which locates a suitable
> kernel and initrd, constructs the kernel command line, etc.). The
> script must either:
> 
>   A. know somehow if the currently running kernel implements
>      kexec_file_load(2), or
> 
>   B. try one method first, and if it fails, retry with the other.
> 
> I agree that kexec(1) should probably allow the user to force a
> specific method, but I don't see the benefit of implementing fallback
> in an external script and not in kexec-tools itself.
> 
> OTOH if you want to push the fallback logic out of kexec-tools, then I
> would like to get better diagnostic at least. Letting my script parse
> kexec output is, um, suboptimal.

Thanks for the details!

Firstly, this patch is very ugly. It mixs the falling back issue, doc
adding, code cleanup in one patch. It's not easy to see how many lines
of code change involved.

Secondly, I personally like better the A or B two options. For A,
checking ARCH in script might be a easier thing. And for B, just check
if "syscall kexec_file_load not available" is printed, then retry the
KEXEC_LOAD.

And the falling back may give people a feeling that that ARCH support
the file mode loading. Besides, if fall back to KEXEC_LOAD when
KEXEC_FILE_LOAD is tried but not supported this time, next time people
may want to do fall back when KEXEC_FILE_LOAD is tried but failed,
since there has been a precedent. This might be not good for keeping
code logic simple, add complexity to maintaining.

My personal opinion.

Thanks
Baoquan

> > > Also provide an option to call the old syscall in case the new syscall
> > > fails with other reason than ENOSYS.
> > > 
> > > Also document the options.
> > > 
> > > Signed-off-by: Michal Suchanek <msucha...@suse.de>
> > > ---
> > >  kexec/kexec.8 |  9 +++++++++
> > >  kexec/kexec.c | 41 +++++++++++++++--------------------------
> > >  kexec/kexec.h |  2 ++
> > >  3 files changed, 26 insertions(+), 26 deletions(-)
> > > 
> > > diff --git a/kexec/kexec.8 b/kexec/kexec.8
> > > index e0131b4ea827..7e4df723251d 100644
> > > --- a/kexec/kexec.8
> > > +++ b/kexec/kexec.8
> > > @@ -144,6 +144,15 @@ Load the new kernel for use on panic.
> > >  Specify that the new kernel is of this
> > >  .I type.
> > >  .TP
> > > +.BI \-s\ (\-\-kexec-file-syscall)
> > > +Specify that the new KEXEC_FILE_LOAD syscall should be used exclusively.
> > > +Otherwise KEXEC_FILE_LOAD is tried and when not supported KEXEC_LOAD is 
> > > used.
> > > +.I type.
> > > +.TP
> > > +.BI \-c\ (\-\-kexec-syscall)
> > > +Specify that the old KEXEC_LOAD syscall should be used exclusively.
> > > +.I type.
> > > +.TP
> > >  .B \-u\ (\-\-unload)
> > >  Unload the current
> > >  .B kexec
> > > diff --git a/kexec/kexec.c b/kexec/kexec.c
> > > index cfd837c1b6bb..25328c02b508 100644
> > > --- a/kexec/kexec.c
> > > +++ b/kexec/kexec.c
> > > @@ -1166,7 +1166,7 @@ static int do_kexec_file_load(int fileind, int 
> > > argc, char **argv,
> > >  
> > >   if (!is_kexec_file_load_implemented()) {
> > >           fprintf(stderr, "syscall kexec_file_load not available.\n");
> > > -         return -1;
> > > +         return -ENOSYS;
> > >   }
> > >  
> > >   if (argc - fileind <= 0) {
> > > @@ -1243,6 +1243,7 @@ int main(int argc, char *argv[])
> > >   int do_unload = 0;
> > >   int do_reuse_initrd = 0;
> > >   int do_kexec_file_syscall = 0;
> > > + int do_kexec_syscall = 0;
> > >   int do_status = 0;
> > >   void *entry = 0;
> > >   char *type = 0;
> > > @@ -1256,19 +1257,6 @@ int main(int argc, char *argv[])
> > >   };
> > >   static const char short_options[] = KEXEC_ALL_OPT_STR;
> > >  
> > > - /*
> > > -  * First check if --use-kexec-file-syscall is set. That changes lot of
> > > -  * things
> > > -  */
> > > - while ((opt = getopt_long(argc, argv, short_options,
> > > -                           options, 0)) != -1) {
> > > -         switch(opt) {
> > > -         case OPT_KEXEC_FILE_SYSCALL:
> > > -                 do_kexec_file_syscall = 1;
> > > -                 break;
> > > -         }
> > > - }
> > > -
> > >   /* Reset getopt for the next pass. */
> > >   opterr = 1;
> > >   optind = 1;
> > > @@ -1310,8 +1298,7 @@ int main(int argc, char *argv[])
> > >                   do_shutdown = 0;
> > >                   do_sync = 0;
> > >                   do_unload = 1;
> > > -                 if (do_kexec_file_syscall)
> > > -                         kexec_file_flags |= KEXEC_FILE_UNLOAD;
> > > +                 kexec_file_flags |= KEXEC_FILE_UNLOAD;
> > >                   break;
> > >           case OPT_EXEC:
> > >                   do_load = 0;
> > > @@ -1354,11 +1341,8 @@ int main(int argc, char *argv[])
> > >                   do_exec = 0;
> > >                   do_shutdown = 0;
> > >                   do_sync = 0;
> > > -                 if (do_kexec_file_syscall)
> > > -                         kexec_file_flags |= KEXEC_FILE_ON_CRASH;
> > > -                 else
> > > -                         kexec_flags = KEXEC_ON_CRASH;
> > > -                 break;
> > > +                 kexec_file_flags |= KEXEC_FILE_ON_CRASH;
> > > +                 kexec_flags = KEXEC_ON_CRASH;
> > >           case OPT_MEM_MIN:
> > >                   mem_min = strtoul(optarg, &endptr, 0);
> > >                   if (*endptr) {
> > > @@ -1383,7 +1367,12 @@ int main(int argc, char *argv[])
> > >                   do_reuse_initrd = 1;
> > >                   break;
> > >           case OPT_KEXEC_FILE_SYSCALL:
> > > -                 /* We already parsed it. Nothing to do. */
> > > +                 do_kexec_file_syscall = 1;
> > > +                 do_kexec_syscall = 0;
> > > +                 break;
> > > +         case OPT_KEXEC_SYSCALL:
> > > +                 do_kexec_file_syscall = 0;
> > > +                 do_kexec_syscall = 1;
> > >                   break;
> > >           case OPT_STATUS:
> > >                   do_status = 1;
> > > @@ -1456,16 +1445,16 @@ int main(int argc, char *argv[])
> > >           result = k_status(kexec_flags);
> > >   }
> > >   if (do_unload) {
> > > -         if (do_kexec_file_syscall)
> > > +         if (!do_kexec_syscall)
> > >                   result = kexec_file_unload(kexec_file_flags);
> > > -         else
> > > +         if ((result == -ENOSYS) || !do_kexec_file_syscall)
> > >                   result = k_unload(kexec_flags);
> > >   }
> > >   if (do_load && (result == 0)) {
> > > -         if (do_kexec_file_syscall)
> > > +         if (!do_kexec_syscall)
> > >                   result = do_kexec_file_load(fileind, argc, argv,
> > >                                            kexec_file_flags);
> > > -         else
> > > +         if ((result == -ENOSYS) || !do_kexec_file_syscall)
> > >                   result = my_load(type, fileind, argc, argv,
> > >                                           kexec_flags, entry);
> > >   }
> > > diff --git a/kexec/kexec.h b/kexec/kexec.h
> > > index 26225d2c002a..7abcec796cae 100644
> > > --- a/kexec/kexec.h
> > > +++ b/kexec/kexec.h
> > > @@ -219,6 +219,7 @@ extern int file_types;
> > >  #define OPT_TYPE         't'
> > >  #define OPT_PANIC                'p'
> > >  #define OPT_KEXEC_FILE_SYSCALL   's'
> > > +#define OPT_KEXEC_SYSCALL        'c'
> > >  #define OPT_STATUS               'S'
> > >  #define OPT_MEM_MIN             256
> > >  #define OPT_MEM_MAX             257
> > > @@ -246,6 +247,7 @@ 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 }, \
> > > + { "kexec-syscall",      0, 0, OPT_KEXEC_SYSCALL }, \
> > >   { "debug",              0, 0, OPT_DEBUG }, \
> > >   { "status",             0, 0, OPT_STATUS }, \
> > >   { "print-ckr-size",     0, 0, OPT_PRINT_CKR_SIZE }, \
> > > -- 
> > > 2.13.6
> > > 
> > > 
> > > _______________________________________________
> > > kexec mailing list
> > > kexec@lists.infradead.org
> > > http://lists.infradead.org/mailman/listinfo/kexec  
> > 
> > _______________________________________________
> > kexec mailing list
> > kexec@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/kexec
> 
> 
> _______________________________________________
> kexec mailing list
> kexec@lists.infradead.org
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