Re: [PATCH for-8.2 v2 1/2] qapi/migration: Deduplicate migration parameter field comments

[Daniel P . Berrangé]

On Fri, Aug 04, 2023 at 12:46:18PM -0400, Peter Xu wrote:
> On Fri, Aug 04, 2023 at 05:29:19PM +0100, Daniel P. Berrangé wrote:
> > On Fri, Aug 04, 2023 at 12:01:54PM -0400, Peter Xu wrote:
> > > On Fri, Aug 04, 2023 at 02:59:07PM +0100, Daniel P. Berrangé wrote:
> > > > On Fri, Aug 04, 2023 at 02:28:05PM +0200, Markus Armbruster wrote:
> > > > > Peter Xu <peterx@redhat.com> writes:
> > > > > 
> > > > > > We used to have three objects that have always the same list of 
> > > > > > parameters
> > > > > 
> > > > > We have!
> > > > > 
> > > > > > and comments are always duplicated:
> > > > > >
> > > > > >   - @MigrationParameter
> > > > > >   - @MigrationParameters
> > > > > >   - @MigrateSetParameters
> > > > > >
> > > > > > Before we can deduplicate the code, it's fairly straightforward to
> > > > > > deduplicate the comments first, so for each time we add a new 
> > > > > > migration
> > > > > > parameter we don't need to copy the same paragraphs three times.
> > > > > 
> > > > > De-duplicating the code would be nice, but we haven't done so in 
> > > > > years,
> > > > > which suggests it's hard enough not to be worth the trouble.
> > > > 
> > > > The "MigrationParameter" enumeration isn't actually used in
> > > > QMP at all.
> > > > 
> > > > It is only used in HMP for hmp_migrate_set_parameter and
> > > > hmp_info_migrate_parameters. So it is questionable documenting
> > > > that enum in the QMP reference docs at all.
> > > > 
> > > > 1c1
> > > > < { 'struct': 'MigrationParameters',
> > > > ---
> > > > > { 'struct': 'MigrateSetParameters',
> > > > 14,16c14,16
> > > > <             '*tls-creds': 'str',
> > > > <             '*tls-hostname': 'str',
> > > > <             '*tls-authz': 'str',
> > > > ---
> > > > >             '*tls-creds': 'StrOrNull',
> > > > >             '*tls-hostname': 'StrOrNull',
> > > > >             '*tls-authz': 'StrOrNull',
> > > > 
> > > > Is it not valid to use StrOrNull in both cases and thus
> > > > delete the duplication here ?
> > > 
> > > I tested removing MigrateSetParameters by replacing it with
> > > MigrationParameters and it looks all fine here... I manually tested 
> > > qmp/hmp
> > > on set/query parameters, and qtests are all happy.
> > 
> > I meant the other way around, such we would be using 'StrOrNull'
> > in all scenarios.
> 
> Yes, that should also work and even without worrying on nulls.  I just took
> a random one replacing the other.
> 
> > 
> > > 
> > > The only thing I see that may affect it is we used to logically allow
> > > taking things like '"tls-authz": null' in the json input, but now we won't
> > > allow that because we'll be asking for a string type only.
> > > 
> > > Since we have query-qmp-schema I suppose we're all fine, because logically
> > > the mgmt app (libvirt?) will still query that to understand the protocol,
> > > so now we'll have (response of query-qmp-schema):
> > > 
> > >         {
> > >             "arg-type": "144",
> > >             "meta-type": "command",
> > >             "name": "migrate-set-parameters",
> > >             "ret-type": "0"
> > >         },
> > > 
> > > Where 144 can start to point to MigrationParameters, rather than
> > > MigrateSetParameters.
> > > 
> > > Ok, then what if the mgmt app doesn't care and just used "null" in tls-*
> > > fields when setting?  Funnily I tried it and actually anything that does
> > > migrate-set-parameters with a "null" passed over to tls-* fields will
> > > already crash qemu...
> > > 
> > > ./migration/options.c:1333: migrate_params_apply: Assertion 
> > > `params->tls_authz->type == QTYPE_QSTRING' failed.
> > > 
> > > #0  0x00007f72f4b2a844 in __pthread_kill_implementation () at 
> > > /lib64/libc.so.6
> > > #1  0x00007f72f4ad9abe in raise () at /lib64/libc.so.6
> > > #2  0x00007f72f4ac287f in abort () at /lib64/libc.so.6
> > > #3  0x00007f72f4ac279b in _nl_load_domain.cold () at /lib64/libc.so.6
> > > #4  0x00007f72f4ad2147 in  () at /lib64/libc.so.6
> > > #5  0x00005573308740e6 in migrate_params_apply (params=0x7ffc74fd09d0, 
> > > errp=0x7ffc74fd0998) at ../migration/options.c:1333
> > > #6  0x0000557330874591 in qmp_migrate_set_parameters 
> > > (params=0x7ffc74fd09d0, errp=0x7ffc74fd0998) at 
> > > ../migration/options.c:1433
> > > #7  0x0000557330cb9132 in qmp_marshal_migrate_set_parameters 
> > > (args=0x7f72e00036d0, ret=0x7f72f133cd98, errp=0x7f72f133cd90) at 
> > > qapi/qapi-commands-migration.c:214
> > > #8  0x0000557330d07fab in do_qmp_dispatch_bh (opaque=0x7f72f133ce30) at 
> > > ../qapi/qmp-dispatch.c:128
> > > #9  0x0000557330d33bbb in aio_bh_call (bh=0x5573337d7920) at 
> > > ../util/async.c:169
> > > #10 0x0000557330d33cd8 in aio_bh_poll (ctx=0x55733356e7d0) at 
> > > ../util/async.c:216
> > > #11 0x0000557330d17a19 in aio_dispatch (ctx=0x55733356e7d0) at 
> > > ../util/aio-posix.c:423
> > > #12 0x0000557330d34117 in aio_ctx_dispatch (source=0x55733356e7d0, 
> > > callback=0x0, user_data=0x0) at ../util/async.c:358
> > > #13 0x00007f72f5a8848c in g_main_context_dispatch () at 
> > > /lib64/libglib-2.0.so.0
> > > #14 0x0000557330d358d4 in glib_pollfds_poll () at ../util/main-loop.c:290
> > > #15 0x0000557330d35951 in os_host_main_loop_wait (timeout=0) at 
> > > ../util/main-loop.c:313
> > > #16 0x0000557330d35a5f in main_loop_wait (nonblocking=0) at 
> > > ../util/main-loop.c:592
> > > #17 0x000055733083aee0 in qemu_main_loop () at ../softmmu/runstate.c:732
> > > #18 0x0000557330b0921b in qemu_default_main () at ../softmmu/main.c:37
> > > #19 0x0000557330b09251 in main (argc=35, argv=0x7ffc74fd0ec8) at 
> > > ../softmmu/main.c:48
> > > 
> > > Then I suppose it means all mgmt apps are not using "null" anyway, and it
> > > makes more sense to me to just remove MigrateSetParameters (by replacing 
> > > it
> > > with MigrationParameters).
> > 
> > It shouldn't be crashing,  because qmp_migrate_set_parameters()
> > is turning 'null' into  "", which means the assert ought to
> > never fire. Did you have a local modiification that caused
> > this crash perhaps ?
> 
> I think it just got overlooked when introducing tls-authz to not have added
> that special code in qmp_migrate_set_parameters(), the other two are fine.

Oh right yes, pre-existing bug.

With regards,
Daniel
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