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[99.254.121.117]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2079473d080sm80389065ad.284.2024.09.19.06.43.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Sep 2024 06:43:18 -0700 (PDT) Date: Thu, 19 Sep 2024 09:43:08 -0400 From: Peter Xu To: "Dr. David Alan Gilbert" Cc: Fabiano Rosas , Markus Armbruster , eblake@redhat.com, qemu-devel@nongnu.org Subject: Re: [PATCH 2/3] migration: Remove unused zero-blocks capability Message-ID: References: <20240918000207.182683-1-dave@treblig.org> <20240918000207.182683-3-dave@treblig.org> <87msk54ifb.fsf@pond.sub.org> <87ttecrkqe.fsf@pond.sub.org> <87tteber7o.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Received-SPF: pass client-ip=170.10.129.124; envelope-from=peterx@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, 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: 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 On Thu, Sep 19, 2024 at 01:00:34PM +0000, Dr. David Alan Gilbert wrote: > * Fabiano Rosas (farosas@suse.de) wrote: > > Markus Armbruster writes: > > > > > Peter Xu writes: > > > > > >> On Wed, Sep 18, 2024 at 07:52:56AM +0200, Markus Armbruster wrote: > > >>> dave@treblig.org writes: > > >>> > > >>> > From: "Dr. David Alan Gilbert" > > >>> > > > >>> > migrate_zero_blocks is unused since > > >>> > eef0bae3a7 ("migration: Remove block migration") > > >>> > > > >>> > Remove it. > > >>> > That whole zero-blocks capability was just for old-school > > >>> > block migration anyway. > > >>> > > > >>> > Remove the capability as well. > > >>> > > > >>> > Signed-off-by: Dr. David Alan Gilbert > > >>> > --- > > >>> > migration/options.c | 8 -------- > > >>> > migration/options.h | 1 - > > >>> > qapi/migration.json | 10 +--------- > > >>> > 3 files changed, 1 insertion(+), 18 deletions(-) > > >>> > > > >>> > diff --git a/migration/options.c b/migration/options.c > > >>> > index 9460c5dee9..997e060612 100644 > > >>> > --- a/migration/options.c > > >>> > +++ b/migration/options.c > > >>> > @@ -177,7 +177,6 @@ Property migration_properties[] = { > > >>> > DEFINE_PROP_MIG_CAP("x-xbzrle", MIGRATION_CAPABILITY_XBZRLE), > > >>> > DEFINE_PROP_MIG_CAP("x-rdma-pin-all", MIGRATION_CAPABILITY_RDMA_PIN_ALL), > > >>> > DEFINE_PROP_MIG_CAP("x-auto-converge", MIGRATION_CAPABILITY_AUTO_CONVERGE), > > >>> > - DEFINE_PROP_MIG_CAP("x-zero-blocks", MIGRATION_CAPABILITY_ZERO_BLOCKS), > > >>> > DEFINE_PROP_MIG_CAP("x-events", MIGRATION_CAPABILITY_EVENTS), > > >>> > DEFINE_PROP_MIG_CAP("x-postcopy-ram", MIGRATION_CAPABILITY_POSTCOPY_RAM), > > >>> > DEFINE_PROP_MIG_CAP("x-postcopy-preempt", > > >>> > > >>> Property of (pseudo-)device "migration". The "x-" prefix suggests we > > >>> expect management software not to rely on it. Okay. > > >>> > > >>> [...] > > >>> > > >>> > diff --git a/qapi/migration.json b/qapi/migration.json > > >>> > index b66cccf107..82d0fc962e 100644 > > >>> > --- a/qapi/migration.json > > >>> > +++ b/qapi/migration.json > > >>> > @@ -389,13 +389,6 @@ > > >>> > # footprint is mlock()'d on demand or all at once. Refer to > > >>> > # docs/rdma.txt for usage. Disabled by default. (since 2.0) > > >>> > # > > >>> > -# @zero-blocks: During storage migration encode blocks of zeroes > > >>> > -# efficiently. This essentially saves 1MB of zeroes per block on > > >>> > -# the wire. Enabling requires source and target VM to support > > >>> > -# this feature. To enable it is sufficient to enable the > > >>> > -# capability on the source VM. The feature is disabled by > > >>> > -# default. (since 1.6) > > >>> > -# > > >>> > # @events: generate events for each migration state change (since 2.4) > > >>> > # > > >>> > # @auto-converge: If enabled, QEMU will automatically throttle down > > >>> > @@ -483,7 +476,7 @@ > > >>> > # Since: 1.2 > > >>> > ## > > >>> > { 'enum': 'MigrationCapability', > > >>> > - 'data': ['xbzrle', 'rdma-pin-all', 'auto-converge', 'zero-blocks', > > >>> > + 'data': ['xbzrle', 'rdma-pin-all', 'auto-converge', > > >>> > 'events', 'postcopy-ram', > > >>> > { 'name': 'x-colo', 'features': [ 'unstable' ] }, > > >>> > 'release-ram', > > >>> > > >>> This is used by migrate-set-capabilities and query-migrate-capabilities, > > >>> via ['MigrationCapabilityStatus']. > > >>> > > >>> query-migrate-capabilities is unaffected: it couldn't return zero-blocks > > >>> anymore even before the patch. > > >>> > > >>> migrate-set-capabilities changes incompatibly, I'm afraid. Before the > > >>> patch: > > >>> > > >>> {"execute": "migrate-set-capabilities", "arguments": {"capabilities": [{"capability": "zero-blocks", "state": true}]}} > > >>> {"return": {}} > > >>> > > >>> Afterwards: > > >>> > > >>> {"error": {"class": "GenericError", "desc": "Parameter 'capability' does not accept value 'zero-blocks'"}} > > >>> > > >>> If we had somehow rejected the capability when it made no sense, > > >>> removing it now it never makes sense would be obviously fine. > > >>> > > >>> The straight & narrow path is to deprecate now, remove later. > > >> > > >> I wonder whether we can make this one simpler, as IIUC this cap depends on > > >> the block migration feature, which properly went through the deprecation > > >> process and got removed in the previous release. > > >> > > >> IOW, currently QEMU behaves the same with this cap on/off, ignoring it > > >> completely. I think it means the deprecation message (even if we provide > > >> some for two extra releases..) wouldn't be anything helpful as anyone who > > >> uses this feature already got affected before this patch.. this feature, > > >> together with block migration, are simply all gone already? > > > > > > We break compatibility for users who supply capability @zero-blocks even > > > though they are not using block migration. > > > > > > Before this patch, the capability is silently ignored. > > > > > > Afterwards, we reject it. > > > > > > This harmless misuse was *not* affected by our prior removal of block > > > migration. > > > > > > It *is* affected by the proposed removal of the capability. > > > > How does this policy_skip thing works? Could we automatically warn > > whenever a capability has the 'deprecated' feature in migration.json? > > > > Also, some of the incompatibility errors in migrate_caps_check() could > > be simplified with something like a new: > > 'features': [ 'conflicts': [ 'cap1', 'cap2' ] ] > > to indicate which caps are incompatible between themselves. > > > > > > > > We either treat this in struct accordance to our rules: deprecate now, > > > remove later. Or we bend our them: > > > > > >>> If we believe nothing relies on it, we can bend the rules and remove > > >>> right away. > > > > > > Not for me to decide. > > > > > > > I'm fine either way, but in any case: > > OK, so I'll split my code to just remove the dead function rather than the > actual capability; Thanks for Fabiano for doing the Deprecation stuff! I'll wait for a final ACK from Markus, then I can queue below patch directly into migration-next. Thanks all! > > Dave > > > -- >8 -- > > >From 3ff313a52e37b8cb407c900d7a1aa266560aebb7 Mon Sep 17 00:00:00 2001 > > From: Fabiano Rosas > > Date: Thu, 19 Sep 2024 09:49:44 -0300 > > Subject: [PATCH] migration: Deprecate zero-blocks capability > > > > The zero-blocks capability was meant to be used along with the block > > migration, which has been removed already in commit eef0bae3a7 > > ("migration: Remove block migration"). > > > > Setting zero-blocks is currently a noop, but the outright removal of > > the capability would cause and error in case some users are still > > setting it. Put the capability through the deprecation process. > > > > Signed-off-by: Fabiano Rosas > > --- > > docs/about/deprecated.rst | 6 ++++++ > > migration/options.c | 4 ++++ > > qapi/migration.json | 5 ++++- > > 3 files changed, 14 insertions(+), 1 deletion(-) > > > > diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst > > index ed31d4b0b2..47cabb6fcc 100644 > > --- a/docs/about/deprecated.rst > > +++ b/docs/about/deprecated.rst > > @@ -476,3 +476,9 @@ usage of providing a file descriptor to a plain file has been > > deprecated in favor of explicitly using the ``file:`` URI with the > > file descriptor being passed as an ``fdset``. Refer to the ``add-fd`` > > command documentation for details on the ``fdset`` usage. > > + > > +``zero-blocks`` capability (since 9.2) > > +'''''''''''''''''''''''''''''''''''''' > > + > > +The ``zero-blocks`` capability was part of the block migration which > > +doesn't exist anymore since it was removed in QEMU v9.1. > > diff --git a/migration/options.c b/migration/options.c > > index 147cd2b8fd..b828bad0d9 100644 > > --- a/migration/options.c > > +++ b/migration/options.c > > @@ -457,6 +457,10 @@ bool migrate_caps_check(bool *old_caps, bool *new_caps, Error **errp) > > ERRP_GUARD(); > > MigrationIncomingState *mis = migration_incoming_get_current(); > > > > + if (new_caps[MIGRATION_CAPABILITY_ZERO_BLOCKS]) { > > + warn_report("zero-blocks capability is deprecated"); > > + } > > + > > #ifndef CONFIG_REPLICATION > > if (new_caps[MIGRATION_CAPABILITY_X_COLO]) { > > error_setg(errp, "QEMU compiled without replication module" > > diff --git a/qapi/migration.json b/qapi/migration.json > > index b66cccf107..3af6aa1740 100644 > > --- a/qapi/migration.json > > +++ b/qapi/migration.json > > @@ -479,11 +479,14 @@ > > # Features: > > # > > # @unstable: Members @x-colo and @x-ignore-shared are experimental. > > +# @deprecated: Member @zero-blocks is deprecated as being part of > > +# block migration which was already removed. > > # > > # Since: 1.2 > > ## > > { 'enum': 'MigrationCapability', > > - 'data': ['xbzrle', 'rdma-pin-all', 'auto-converge', 'zero-blocks', > > + 'data': ['xbzrle', 'rdma-pin-all', 'auto-converge', > > + { 'name': 'zero-blocks', 'features': [ 'deprecated' ] }, > > 'events', 'postcopy-ram', > > { 'name': 'x-colo', 'features': [ 'unstable' ] }, > > 'release-ram', > > -- > > 2.35.3 > > > -- > -----Open up your eyes, open up your mind, open up your code ------- > / Dr. David Alan Gilbert | Running GNU/Linux | Happy \ > \ dave @ treblig.org | | In Hex / > \ _________________________|_____ http://www.treblig.org |_______/ > -- Peter Xu