From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 29F60CDD56F for ; Thu, 19 Sep 2024 13:01:12 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1srGmI-0007cO-MP; Thu, 19 Sep 2024 09:00:58 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1srGm2-0007VX-Rg for qemu-devel@nongnu.org; Thu, 19 Sep 2024 09:00:44 -0400 Received: from mx.treblig.org ([2a00:1098:5b::1]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1srGly-0008H3-UN for qemu-devel@nongnu.org; Thu, 19 Sep 2024 09:00:42 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=treblig.org ; s=bytemarkmx; h=Content-Type:MIME-Version:Message-ID:Subject:From:Date:From :Subject; bh=+hFMzqNydeSJA06lUWtRksv4/SAG4KXCx6CD3FpiZQs=; b=UfHWj+R1/bwRMQpd W0RXu/eHirS4DmmvIDt4zHMiJwwQWuZQv7gvq4U4bfSmzoTlwhDlyBkW4/q/2Z+yQvaPkvoLMcEyS XJhXqXlJA5GxiketsAloCoMcoK/qB2kVYtmsg1LldJwgLeU3HcsJQlYdeST5hH38tX5v7/5OccV4p ZmsCsfcx+QpkFtcr7WmJNtOcaQUGJ9QuQgEo8FNHSy22WNWKQqn5esEdSVLY2EL7GzOqYMPtphpp/ GBqa5sA5oQij6SrtMJ8ftRLEc2N08qKwg0DbmL91TlR2KiT/gDnhZrjsRrvmO05phVc2anQHs2t7+ H7j52NItghh37o7uDw==; Received: from dg by mx.treblig.org with local (Exim 4.96) (envelope-from ) id 1srGlu-006Q4d-0O; Thu, 19 Sep 2024 13:00:34 +0000 Date: Thu, 19 Sep 2024 13:00:34 +0000 From: "Dr. David Alan Gilbert" To: Fabiano Rosas Cc: Markus Armbruster , Peter Xu , 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=iso-8859-1 Content-Disposition: inline In-Reply-To: <87tteber7o.fsf@suse.de> X-Chocolate: 70 percent or better cocoa solids preferably X-Operating-System: Linux/6.1.0-21-amd64 (x86_64) X-Uptime: 12:59:35 up 134 days, 13 min, 1 user, load average: 0.02, 0.01, 0.00 User-Agent: Mutt/2.2.12 (2023-09-09) Received-SPF: pass client-ip=2a00:1098:5b::1; envelope-from=dg@treblig.org; helo=mx.treblig.org 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, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, 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 * 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! 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 |_______/