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[99.254.144.39]) by smtp.gmail.com with ESMTPSA id 27-20020a05620a071b00b007659935ce64sm4950952qkc.71.2023.09.26.12.05.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 26 Sep 2023 12:05:37 -0700 (PDT) Date: Tue, 26 Sep 2023 15:05:34 -0400 From: Peter Xu To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Richard Henderson , qemu-devel@nongnu.org, Juan Quintela , Fabiano Rosas , Thomas Huth , Markus Armbruster Subject: Re: [PATCH v3 4/4] migration/qapi: Drop @MigrationParameter enum Message-ID: References: <20230905162335.235619-1-peterx@redhat.com> <20230905162335.235619-5-peterx@redhat.com> <2edd3a6f-f23d-9a77-db47-4288fe3dbb44@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit 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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, T_SPF_TEMPERROR=0.01 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 Wed, Sep 06, 2023 at 11:46:16AM +0100, Daniel P. Berrangé wrote: > On Wed, Sep 06, 2023 at 12:14:54PM +0200, Philippe Mathieu-Daudé wrote: > > On 6/9/23 11:00, Daniel P. Berrangé wrote: > > > On Wed, Sep 06, 2023 at 06:42:16AM +0200, Philippe Mathieu-Daudé wrote: > > > > On 5/9/23 18:23, Peter Xu wrote: > > > > > Drop the enum in qapi because it is never used in QMP APIs. Instead making > > > > > it an internal definition for QEMU so that we can decouple it from QAPI, > > > > > and also we can deduplicate the QAPI documentations. > > > > > > > > > > Reviewed-by: Daniel P. Berrangé > > > > > Signed-off-by: Peter Xu > > > > > --- > > > > > qapi/migration.json | 179 --------------------------------- > > > > > migration/options.h | 47 +++++++++ > > > > > migration/migration-hmp-cmds.c | 3 +- > > > > > migration/options.c | 51 ++++++++++ > > > > > 4 files changed, 100 insertions(+), 180 deletions(-) > > > > > > > > > > > > > diff --git a/migration/options.h b/migration/options.h > > > > > index 124a5d450f..4591545c62 100644 > > > > > --- a/migration/options.h > > > > > +++ b/migration/options.h > > > > > @@ -66,6 +66,53 @@ bool migrate_cap_set(int cap, bool value, Error **errp); > > > > > /* parameters */ > > > > > +typedef enum { > > > > > + MIGRATION_PARAMETER_ANNOUNCE_INITIAL, > > > > > + MIGRATION_PARAMETER_ANNOUNCE_MAX, > > > > > + MIGRATION_PARAMETER_ANNOUNCE_ROUNDS, > > > > > + MIGRATION_PARAMETER_ANNOUNCE_STEP, > > > > > + MIGRATION_PARAMETER_COMPRESS_LEVEL, > > > > > + MIGRATION_PARAMETER_COMPRESS_THREADS, > > > > > + MIGRATION_PARAMETER_DECOMPRESS_THREADS, > > > > > + MIGRATION_PARAMETER_COMPRESS_WAIT_THREAD, > > > > > + MIGRATION_PARAMETER_THROTTLE_TRIGGER_THRESHOLD, > > > > > + MIGRATION_PARAMETER_CPU_THROTTLE_INITIAL, > > > > > + MIGRATION_PARAMETER_CPU_THROTTLE_INCREMENT, > > > > > + MIGRATION_PARAMETER_CPU_THROTTLE_TAILSLOW, > > > > > + MIGRATION_PARAMETER_TLS_CREDS, > > > > > + MIGRATION_PARAMETER_TLS_HOSTNAME, > > > > > + MIGRATION_PARAMETER_TLS_AUTHZ, > > > > > + MIGRATION_PARAMETER_MAX_BANDWIDTH, > > > > > + MIGRATION_PARAMETER_DOWNTIME_LIMIT, > > > > > + MIGRATION_PARAMETER_X_CHECKPOINT_DELAY, > > > > > + MIGRATION_PARAMETER_BLOCK_INCREMENTAL, > > > > > + MIGRATION_PARAMETER_MULTIFD_CHANNELS, > > > > > + MIGRATION_PARAMETER_XBZRLE_CACHE_SIZE, > > > > > + MIGRATION_PARAMETER_MAX_POSTCOPY_BANDWIDTH, > > > > > + MIGRATION_PARAMETER_MAX_CPU_THROTTLE, > > > > > + MIGRATION_PARAMETER_MULTIFD_COMPRESSION, > > > > > + MIGRATION_PARAMETER_MULTIFD_ZLIB_LEVEL, > > > > > + MIGRATION_PARAMETER_MULTIFD_ZSTD_LEVEL, > > > > > + MIGRATION_PARAMETER_BLOCK_BITMAP_MAPPING, > > > > > + MIGRATION_PARAMETER_X_VCPU_DIRTY_LIMIT_PERIOD, > > > > > + MIGRATION_PARAMETER_VCPU_DIRTY_LIMIT, > > > > > + MIGRATION_PARAMETER__MAX, > > > > > > > > MIGRATION_PARAMETER__MAX is not part of the enum, so: > > > > > > > > #define MIGRATION_PARAMETER__MAX \ > > > > (MIGRATION_PARAMETER_VCPU_DIRTY_LIMIT + 1) > > > > > > IMHO the way it currently is written is better, because the > > > __MAX value is guaranteed to always have the right max value > > > without needing to be manually changed when new params are > > > added. Note this matches the code style used by the QAPI > > > enum generator too. > > > > This concern comes from a previous discussion with Richard (which I > > can't find now in the archives) where he explained to me __MAX is not > > part of the enum set, thus reduces the coverage of compiler sanitizers > > / optimizers, and could introduce subtle bugs. > > > > This motivated this series: > > https://lore.kernel.org/qemu-devel/20230315112811.22355-4-philmd@linaro.org/ > > which should have changed that generated QAPI enum. > > > > (I didn't respin that series because I couldn't find an easy way to > > handle conditionals, see > > https://lore.kernel.org/qemu-devel/87sfdyaq0m.fsf@pond.sub.org/) > > Oh, I completely forgot about that series. > > So the original problem is that with '-Wswitch' present, if the > switched variable is an enum type, the compiler complains if you > don't list all possible enum values, or have a default: clause. > > Thus the existance of __MAX forces use to add case ...__MAX, or > have a default, and you wanted to eliminate that requirement. > > Or the surface that sounds reasonable, but I actually think that > is the conceptually wrong approach from a robustness POV. > > C (and some other languages) are terrible wrt enum declared > constants vs actual stored values. > > You can have a variable declared KeyValueKind and it can store > absolutely any integer value at all, whether intentionally, > or by a code mistake or by data corruption. > > In your example you modified: > > switch (key->key->type) { > case KEY_VALUE_KIND_NUMBER: > qcode = qemu_input_key_number_to_qcode(key->key->u.number.data); > name = QKeyCode_str(qcode); > trace_input_event_key_number(idx, key->key->u.number.data, > name, key->down); > break; > case KEY_VALUE_KIND_QCODE: > name = QKeyCode_str(key->key->u.qcode.data); > trace_input_event_key_qcode(idx, name, key->down); > break; > case KEY_VALUE_KIND__MAX: > /* keep gcc happy */ > break; > } > > to remove KEY_VALUE_KIND__MAX. > > What we should actually do IMHO is to either change it to > > default: > g_assert_not_reached(); > > Or get extra paranoid and -Wswitch-enum too and list both > together > > case KEY_VALUE_KIND__MAX: > default: > g_assert_not_reached(); > > This forces us to validate every enum case, and also protect > against out of range values. > > This is a little more verbose to code, but I can't say it > has been a maint problem in libvirt where we've followed > this approach with -Wswitch-enum and _MAX constants. > > > Back to this patch, I don't object to having MIGRATION_PARAMETER__MAX > > in the enum, but I'd rather have the suggestion below considered. > > I just prefer to see consistency in approach across the codebase, and > currently we use __MAX approach. Personally I prefer the same. I'll squash below change into the patch (with Phil's R-b): =============== diff --git a/migration/options.h b/migration/options.h index 4591545c62..2e4fa17351 100644 --- a/migration/options.h +++ b/migration/options.h @@ -99,8 +99,7 @@ typedef enum { MIGRATION_PARAMETER__MAX, } MigrationParameter; -extern const char *MigrationParameter_string[MIGRATION_PARAMETER__MAX]; -#define MigrationParameter_str(p) MigrationParameter_string[p] +const char *MigrationParameter_str(MigrationParameter p); /** * @MigrationParameter_from_str(): Parse string into a MigrationParameter diff --git a/migration/options.c b/migration/options.c index c9b90d932d..e87c9667d1 100644 --- a/migration/options.c +++ b/migration/options.c @@ -84,7 +84,7 @@ #define DEFAULT_MIGRATE_VCPU_DIRTY_LIMIT_PERIOD 1000 /* milliseconds */ #define DEFAULT_MIGRATE_VCPU_DIRTY_LIMIT 1 /* MB/s */ -const char *MigrationParameter_string[MIGRATION_PARAMETER__MAX] = { +static const char *const MigrationParameter_string[MIGRATION_PARAMETER__MAX] = { [MIGRATION_PARAMETER_ANNOUNCE_INITIAL] = "announce-initial", [MIGRATION_PARAMETER_ANNOUNCE_MAX] = "announce-max", [MIGRATION_PARAMETER_ANNOUNCE_ROUNDS] = "announce-rounds", @@ -116,6 +116,11 @@ const char *MigrationParameter_string[MIGRATION_PARAMETER__MAX] = { [MIGRATION_PARAMETER_VCPU_DIRTY_LIMIT] = "vcpu-dirty-limit", }; +const char *MigrationParameter_str(MigrationParameter p) +{ + return MigrationParameter_string[p]; +} + int MigrationParameter_from_str(const char *param, Error **errp) { int i; =============== Thanks, -- Peter Xu