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Tsirkin" , Markus Armbruster , Eric Blake , "Maciej S. Szmigiero" , Jason Wang , Ben Chaney , Vladimir Sementsov-Ogievskiy Subject: Re: [PATCH RFC 1/2] migration/vl: Allow set parameters with -incoming config:* In-Reply-To: <20260528212947.368132-2-peterx@redhat.com> References: <20260528212947.368132-1-peterx@redhat.com> <20260528212947.368132-2-peterx@redhat.com> Date: Thu, 28 May 2026 19:16:57 -0300 Message-ID: <87pl2ftc12.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Rspamd-Action: no action X-Rspamd-Queue-Id: 63AD066D77 X-Spamd-Result: default: False [-4.51 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RCVD_VIA_SMTP_AUTH(0.00)[]; MISSING_XM_UA(0.00)[]; ARC_NA(0.00)[]; RCPT_COUNT_TWELVE(0.00)[12]; MIME_TRACE(0.00)[0:+]; RCVD_TLS_ALL(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:mid,suse.de:dkim]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DKIM_TRACE(0.00)[suse.de:+] Received-SPF: pass client-ip=195.135.223.131; envelope-from=farosas@suse.de; helo=smtp-out2.suse.de X-Spam_score_int: -43 X-Spam_score: -4.4 X-Spam_bar: ---- X-Spam_report: (-4.4 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_MED=-2.3, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Peter Xu writes: > QEMU doesn't yet have a good way to specify migration parameters so that > they can be available even during early stage of QEMU boots. It is because > the migration object (who owns the migration parameters) will only be > created after PHASE_LATE_BACKENDS_CREATED. It means anything before it > reading migration parameters is illegal. > > However, QEMU does have special use cases for such, namely only-migratable > flag, and cpr-transfer. Recently, we have one more possible user to read a > to-be-introduced new migration parameters during backend initialization > phase. We can introduce yet another global variable (or per-device > parameter) to bypass this limitation, but we can also seek for a generic > solution that we can setup migration parameters very early, even during > backend initializations. > > See this discussion for more details on the context of the problem: > > https://lore.kernel.org/r/ahdI7Vl5KraK566D@x1.local > > This patch wants to take the latter approach. > > As a start, introduce a new way to specify migration parameters in QEMU > boot commandline, as proposed in the above discussion: > > -incoming config:key1=value1,key2=value2,... > > When specified, QEMU will parse a string formatted MigrationParameters and > keep it. When migration object is created, it will apply all the settings > as initial value. > > Since the application of boot parameters will be after object_new() > completes, it means it happens after all machine compat properties or > -global settings (which should be done during instance_post_init()). > > So far, it's still only a way to specify parameters. All parameters are > not visible before migration object created, like before. Any parameter > that needs to be visible during boot will need to opt-in this feature. > Follow up patches will switch the current users to use this model. > > Signed-off-by: Peter Xu > --- > include/migration/misc.h | 5 ++++ > migration/migration.c | 54 ++++++++++++++++++++++++++++++++++++++++ > system/vl.c | 7 ++++++ > qemu-options.hx | 18 ++++++++++++-- > 4 files changed, 82 insertions(+), 2 deletions(-) > > diff --git a/include/migration/misc.h b/include/migration/misc.h > index 3159a5e53c..aff79b1380 100644 > --- a/include/migration/misc.h > +++ b/include/migration/misc.h > @@ -133,6 +133,11 @@ bool migrate_is_uri(const char *uri); > /* Parse @uri and return @channel, returning true on success */ > bool migrate_uri_parse(const char *uri, MigrationChannel **channel, > Error **errp); > +/* > + * Parse @config_str in form of "config:key1=value1,..." to initialize > + * migration parameters. > + */ > +bool migration_parameters_boot_parse(const char *config_str, Error **errp); > 'boot' is not the right word. Maybe 'early'? > /* migration/multifd-device-state.c */ > typedef struct SaveCompletePrecopyThreadData { > diff --git a/migration/migration.c b/migration/migration.c > index 074d3f2c69..d918be7a44 100644 > --- a/migration/migration.c > +++ b/migration/migration.c > @@ -41,6 +41,7 @@ > #include "qapi/qapi-commands-migration.h" > #include "qapi/qapi-events-migration.h" > #include "qapi/qmp/qerror.h" > +#include "qapi/qobject-input-visitor.h" > #include "qobject/qnull.h" > #include "qemu/rcu.h" > #include "postcopy-ram.h" > @@ -94,6 +95,9 @@ enum mig_rp_message_type { > static MigrationState *current_migration; > static MigrationIncomingState *current_incoming; > > +/* Only used during boot, destroyed after migration object initialized */ > +static MigrationParameters *mig_boot_params; > + > static GSList *migration_blockers[MIG_MODE__MAX]; > > static bool migration_object_check(MigrationState *ms, Error **errp); > @@ -102,6 +106,45 @@ static bool stop_return_path_thread_on_source(MigrationState *s); > static void migration_release_dst_files(MigrationState *ms); > static void migration_completion_end(MigrationState *s); > > +bool migration_parameters_boot_parse(const char *config_str, Error **errp) > +{ > + Visitor *v; > + > + if (mig_boot_params) { > + error_setg(errp, "Only one -incoming config:* is allowed."); > + return false; > + } > + > + v = qobject_input_visitor_new_str(config_str, NULL, errp); > + if (!v) { > + goto fail; > + } > + > + if (!visit_type_MigrationParameters(v, NULL, &mig_boot_params, errp)) { > + goto fail; > + } > + > + visit_free(v); > + return true; > + > +fail: > + visit_free(v); > + return false; > +} > + > +static void migration_parameters_boot_apply(void) > +{ > + if (mig_boot_params) { > + /* > + * This can fail, because qobject visitor doesn't do sanity check > + * on values while parsing. It's not too late; we're still in boot > + * phase. > + */ > + qmp_migrate_set_parameters(mig_boot_params, &error_abort); > + g_clear_pointer(&mig_boot_params, qapi_free_MigrationParameters); > + } > +} > + > static void migration_downtime_start(MigrationState *s) > { > trace_vmstate_downtime_checkpoint("src-downtime-start"); > @@ -322,6 +365,17 @@ void migration_object_init(void) > > current_incoming->exit_on_error = INMIGRATE_DEFAULT_EXIT_ON_ERROR; > > + /* > + * Apply boot migration parameters in case the user specified some via > + * command line "-incoming config:*". NOTE: this will overwrite machine > + * type compat properties and -global settings! > + */ Hmm, but then it's exactly the same as -global migration.* ? Why do we need to extend -incoming? Also, I don't see how qmp_migrate_set_parameters can overwrite compat properties. They're not part of MigrationParameters. > + migration_parameters_boot_apply(); > + > + /* > + * The boot parameters should have been verified already, but leave it > + * after applying boot parameters to do one check for everything. > + */ Will it get expensive? We do that for every QEMU start. > migration_object_check(current_migration, &error_fatal); > > ram_mig_init(); > diff --git a/system/vl.c b/system/vl.c > index da36b2c6e1..49f5fa0c7b 100644 > --- a/system/vl.c > +++ b/system/vl.c > @@ -1838,6 +1838,13 @@ static void incoming_option_parse(const char *str) > > if (!strcmp(str, "defer")) { > channel = NULL; > + } else if (!strncmp(str, "config:", 7)) { > + /* > + * This is not a channel setup, but configuration to incoming > + * migration parameters to make them available during early boot. > + */ > + migration_parameters_boot_parse(str + 7, &error_fatal); > + return; > } else if (migrate_is_uri(str)) { > migrate_uri_parse(str, &channel, &error_fatal); > } else { > diff --git a/qemu-options.hx b/qemu-options.hx > index 96ae41f787..1fc92a409a 100644 > --- a/qemu-options.hx > +++ b/qemu-options.hx > @@ -5366,11 +5366,15 @@ DEF("incoming", HAS_ARG, QEMU_OPTION_incoming, \ > "-incoming \n" \ > " accept incoming migration on the migration channel\n" \ > "-incoming defer\n" \ > - " wait for the URI to be specified via migrate_incoming\n", > + " wait for the URI to be specified via migrate_incoming\n" > + "-incoming config:key1=value1,key2=value2,...\n" \ > + " specify migration parameters valid even during boot\n", > QEMU_ARCH_ALL) > SRST > + > The -incoming option specifies the migration channel for an incoming > -migration. It may be used multiple times to specify multiple > +migration, or can also be used to setup migration parameters for the > +incoming migration. It may be used multiple times to specify multiple > migration channel types. The channel type is specified in , > or is 'main' for all other forms of -incoming. If multiple -incoming > options are specified for a channel type, the last one takes precedence. > @@ -5411,6 +5415,16 @@ options are specified for a channel type, the last one takes precedence. > Wait for the URI to be specified via migrate\_incoming. The monitor > can be used to change settings (such as migration parameters) prior > to issuing the migrate\_incoming to allow the migration to begin. > + > +``-incoming config:key1=value1[,key2=value2,...]`` > + > + Specify migration parameters in QEMU commandlines, so that these command line > + parameters will be available even during very early boot of QEMU. > + They will be applied properly after QEMU boots and when the migration The "applied properly" part is implementation detail. > + core is initialized. From that POV, it has similar effect as setting > + these parameters using QMP command ``migrate-set-parameters`` or HMP > + command ``migrate_set_parameter``. > + > ERST > > DEF("only-migratable", 0, QEMU_OPTION_only_migratable, \