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 X-Spam-Level: X-Spam-Status: No, score=-13.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 07123C433E0 for ; Wed, 17 Feb 2021 15:34:14 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 4AADD64E0F for ; Wed, 17 Feb 2021 15:34:13 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4AADD64E0F Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:54114 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lCOqC-0003iS-AF for qemu-devel@archiver.kernel.org; Wed, 17 Feb 2021 10:34:12 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:45092) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lCOoc-0002mM-7e for qemu-devel@nongnu.org; Wed, 17 Feb 2021 10:32:35 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:30139) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lCOoa-0005b6-0e for qemu-devel@nongnu.org; Wed, 17 Feb 2021 10:32:33 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1613575951; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=hAPXE1Dz1+3yoNBhBwPljRyty+QSg36mk/nzA5mZX48=; b=NDUggHzpeauLclhkR+VVpdcWHlAsa9KlLVejwaZJvxGdbSTpTi8h3VnxY2vMGrYixbt7MP 8fFP+DC0L+M0WSWW2YOM8agB6dKI/UtnYeRqdLvlO8/nipqJ7VeZZfsvyfmJ4jkCWnWgO8 9RLspaf6sJN/hN7w1QhsZAWmymC7BBk= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-564-c-7mi3OFOmeZ7YY7cHBOpQ-1; Wed, 17 Feb 2021 10:32:28 -0500 X-MC-Unique: c-7mi3OFOmeZ7YY7cHBOpQ-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 89B9C6D4E8 for ; Wed, 17 Feb 2021 15:32:27 +0000 (UTC) Received: from blackfin.pond.sub.org (ovpn-115-79.ams2.redhat.com [10.36.115.79]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 07C2C10016FD; Wed, 17 Feb 2021 15:32:26 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 7BF28113860F; Wed, 17 Feb 2021 16:32:25 +0100 (CET) From: Markus Armbruster To: Kevin Wolf Subject: Re: [PATCH v2 4/6] qapi: Apply aliases in qobject-input-visitor References: <20210211183118.422036-1-kwolf@redhat.com> <20210211183118.422036-5-kwolf@redhat.com> Date: Wed, 17 Feb 2021 16:32:25 +0100 In-Reply-To: <20210211183118.422036-5-kwolf@redhat.com> (Kevin Wolf's message of "Thu, 11 Feb 2021 19:31:16 +0100") Message-ID: <871rder9py.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=armbru@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Received-SPF: pass client-ip=63.128.21.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 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_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: jsnow@redhat.com, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Kevin Wolf writes: > When looking for an object in a struct in the external representation, > check not only the currently visited struct, but also whether an alias > in the current StackObject matches and try to fetch the value from the > alias then. Providing two values for the same object through different > aliases is an error. > > Signed-off-by: Kevin Wolf Looking just at qobject_input_try_get_object() for now. > --- > qapi/qobject-input-visitor.c | 214 +++++++++++++++++++++++++++++++++-- > 1 file changed, 205 insertions(+), 9 deletions(-) > > diff --git a/qapi/qobject-input-visitor.c b/qapi/qobject-input-visitor.c > index dd04ef0027..3ea5e5abd6 100644 > --- a/qapi/qobject-input-visitor.c > +++ b/qapi/qobject-input-visitor.c > @@ -95,6 +95,8 @@ struct QObjectInputVisitor { > QObject *root; > bool keyval; /* Assume @root made with keyval_parse() */ > > + QDict *empty_qdict; /* Used for implicit objects */ > + > /* Stack of objects being visited (all entries will be either > * QDict or QList). */ > QSLIST_HEAD(, StackObject) stack; > @@ -167,9 +169,178 @@ static const char *full_name(QObjectInputVisitor *qiv, const char *name) > return full_name_so(qiv, name, false, tos); > } > > +static bool find_object_member(QObjectInputVisitor *qiv, > + StackObject **so, const char **name, > + bool *implicit_object, Error **errp); > + > +/* > + * Check whether the alias member defined by @a is present in the > + * input and can be used to obtain the value for the member @name in > + * the currently visited object. > + */ > +static bool alias_present(QObjectInputVisitor *qiv, > + InputVisitorAlias *a, const char *name) > +{ > + StackObject *so = a->alias_so; > + > + /* > + * The passed source @name is only relevant for wildcard aliases which > + * don't have a separate name, otherwise we use the alias name. > + */ > + if (a->name) { > + name = a->name; > + } > + > + /* > + * Check whether the alias member is present in the input > + * (possibly recursively because aliases are transitive). > + */ > + if (!find_object_member(qiv, &so, &name, NULL, NULL)) { > + return false; > + } > + > + /* > + * Every source can be used only once. If a value in the input would end up > + * being used twice through aliases, we'll fail the second access. > + */ > + if (!g_hash_table_contains(so->h, name)) { > + return false; > + } > + > + return true; > +} > + > +/* > + * Check whether the member @name in the object visited by @so can be > + * specified in the input by using the alias described by @a. > + * > + * If @name is only a prefix of the alias source, but doesn't match > + * immediately, false is returned and @implicit_object is set to true > + * if it is non-NULL. In all other cases, @implicit_object is left > + * unchanged. > + */ > +static bool alias_source_matches(QObjectInputVisitor *qiv, > + StackObject *so, InputVisitorAlias *a, > + const char *name, bool *implicit_object) > +{ > + if (a->src[0] == NULL) { > + assert(a->name == NULL); > + return true; > + } > + > + if (!strcmp(a->src[0], name)) { > + if (a->name && a->src[1] == NULL) { > + /* > + * We're matching an exact member, the source for this alias is > + * immediately in @so. > + */ > + return true; > + } else if (implicit_object) { > + /* > + * We're only looking at a prefix of the source path for the alias. > + * If the input contains no object of the requested name, we will > + * implicitly create an empty one so that the alias can still be > + * used. > + * > + * We want to create the implicit object only if the alias is > + * actually used, but we can't tell here for wildcard aliases (only > + * a later visitor call will determine this). This means that > + * wildcard aliases must never have optional keys in their source > + * path. > + */ > + if (!a->name || alias_present(qiv, a, a->name)) { > + *implicit_object = true; > + } > + } > + } > + > + return false; > +} > + > +/* > + * Find the place in the input where the value for the object member > + * @name in @so is specified, considering applicable aliases. > + * > + * If a value could be found, true is returned and @so and @name are > + * updated to identify the key name and StackObject where the value > + * can be found in the input. (This is either unchanged or the > + * alias_so/name of an alias.) The value of @implicit_object on > + * return is undefined in this case. > + * > + * If no value could be found in the input, false is returned. This > + * is not an error and @errp remains unchanged. If @implicit_object > + * is non-NULL, it is set to true if the given name is a prefix of the > + * source path of an alias for which a value may be present in the > + * input. It is set to false otherwise. > + * > + * If an error occurs (e.g. two values are specified for the member > + * through different names), false is returned and @errp is set. The > + * value of @implicit_object on return is undefined in this case. > + */ > +static bool find_object_member(QObjectInputVisitor *qiv, > + StackObject **so, const char **name, > + bool *implicit_object, Error **errp) > +{ > + StackObject *cur_so = *so; > + QDict *qdict = qobject_to(QDict, cur_so->obj); > + const char *found = NULL; > + bool found_is_wildcard = false; > + InputVisitorAlias *a; > + > + if (implicit_object) { > + *implicit_object = false; > + } > + > + /* Directly present in the container */ > + if (qdict_haskey(qdict, *name)) { > + found = *name; > + } > + > + /* > + * Find aliases whose source path matches @name in this StackObject. We can > + * then get the value with the key a->name from a->alias_so. > + */ > + QSLIST_FOREACH(a, &cur_so->aliases, next) { > + if (a->name == NULL && found) { > + /* > + * Skip wildcard aliases if we already have a match. This is > + * not a conflict that should result in an error. > + */ > + continue; > + } > + > + if (!alias_source_matches(qiv, cur_so, a, *name, implicit_object)) { > + continue; > + } > + > + if (!alias_present(qiv, a, *name)) { > + continue; > + } > + > + if (found && !found_is_wildcard) { > + error_setg(errp, "Value for parameter %s was already given " > + "through an alias", > + full_name_so(qiv, *name, false, *so)); > + return false; > + } else { > + found = a->name ?: *name; > + *so = a->alias_so; > + found_is_wildcard = !a->name; > + } > + } > + > + /* Chained aliases: *so/found might be the source of another alias */ > + if (found && (*so != cur_so || found != *name)) { > + find_object_member(qiv, so, &found, NULL, errp); > + } > + > + *name = found; > + return found; > +} > + > static QObject *qobject_input_try_get_object(QObjectInputVisitor *qiv, > const char *name, > - bool consume) > + bool consume, Error **errp) Reminder: * The @name parameter of visit_type_FOO() describes the relation * between this QAPI value and its parent container. When visiting * the root of a tree, @name is ignored; when visiting a member of an * object, @name is the key associated with the value; when visiting a * member of a list, @name is NULL; and when visiting the member of an * alternate, @name should equal the name used for visiting the * alternate. > { > StackObject *tos; > QObject *qobj; QObject *ret; if (QSLIST_EMPTY(&qiv->stack)) { /* Starting at root, name is ignored. */ assert(qiv->root); return qiv->root; } /* We are in a container; find the next element. */ tos = QSLIST_FIRST(&qiv->stack); qobj = tos->obj; > @@ -187,10 +358,30 @@ static QObject *qobject_input_try_get_object(QObjectInputVisitor *qiv, > assert(qobj); > > if (qobject_type(qobj) == QTYPE_QDICT) { We're visiting a member of object @qobj, which is tos->obj. > - assert(name); > - ret = qdict_get(qobject_to(QDict, qobj), name); > - if (tos->h && consume && ret) { > - bool removed = g_hash_table_remove(tos->h, name); > + StackObject *so = tos; > + const char *key = name; > + bool implicit_object; > + > + assert(key); > + if (!find_object_member(qiv, &so, &key, &implicit_object, errp)) { No input found. > + if (implicit_object) { > + /* > + * The member is not present in the input, but > + * something inside of it might still be given through > + * an alias. Pretend there was an empty object in the > + * input. > + */ Cue me scratching head. find_object_member()'s contract explains @implicit_object is true "if the given name is a prefix of the source path of an alias for which a value may be present in the input." I figure this means qiv->stack has a stack object with an alias whose src[] has a prefix that resolves to @tos (the currently visited object). Visiting the members of the currently visited object may or may not visit something where that src[] resolves completely, and that something may or may not have a member for the alias. If it does, there is input, and "something" will happen to route it to the correct place. What exactly? Should become clearer further down. If it doesn't, there is no input. > + if (!qiv->empty_qdict) { > + qiv->empty_qdict = qdict_new(); > + } > + return QOBJECT(qiv->empty_qdict); So far, I have no idea *why* we pretend there was an empty object in the input, why sharing it is safe, and why changing the return value from null to empty dict is okay. Should become clearer further down. > + } else { > + return NULL; There is definitely no input. The old code returns null then (because the qdict_get() above returns null). No change. Good. > + } > + } We get here only when find_object_member() found input. If no aliases applied, @so and @key are unchanged, i.e. @so is @tos, and @key is @name. The code below is the old code with @qobj replaced by so->obj and @name replaced by @key. No change. Good. Else, some alias (or chain of aliases) applied. Let's assume a single alias for now. It is defined for a stack object further down qiv->stack, with an alias name there, and it's src[] resolves to @tos (the currently visited object). find_object_member() found input there, i.e. the alias stack object's input has a member with the alias name. It changed @so to the alias stack object, and @key to the alias name. The code below then gets the input value from member with the alias name in the alias object. This consumes the "alias member" of the outer input object, and uses it as input for the "true member" of the inner object. Good. I figure a chain of aliases works the same; the only difference is we need more steps to find the alias stack object and name. Correct? > + ret = qdict_get(qobject_to(QDict, so->obj), key); Any particular reason why find_object_member() doesn't simply return the input it found? > + if (so->h && consume && ret) { How can @ret be null? > + bool removed = g_hash_table_remove(so->h, key); > assert(removed); > } > } else { Note that we access the parent container via tos->obj, so->obj, and qobj. Too many aliases for my taste. Let's eliminate qobj. Now let me try to figure out how the magic around @implicit_object works. Okay, I came, I saw, I ran out of brain juice. Help! Please walk me through an example that covers all the paths through this function, unless you have better ideas on how to explain it. > @@ -216,9 +407,10 @@ static QObject *qobject_input_get_object(QObjectInputVisitor *qiv, > const char *name, > bool consume, Error **errp) > { > - QObject *obj = qobject_input_try_get_object(qiv, name, consume); > + ERRP_GUARD(); > + QObject *obj = qobject_input_try_get_object(qiv, name, consume, errp); > > - if (!obj) { > + if (!obj && !*errp) { > error_setg(errp, QERR_MISSING_PARAMETER, full_name(qiv, name)); > } > return obj; > @@ -799,13 +991,16 @@ static bool qobject_input_type_size_keyval(Visitor *v, const char *name, > static void qobject_input_optional(Visitor *v, const char *name, bool *present) > { > QObjectInputVisitor *qiv = to_qiv(v); > - QObject *qobj = qobject_input_try_get_object(qiv, name, false); > + Error *local_err = NULL; > + QObject *qobj = qobject_input_try_get_object(qiv, name, false, &local_err); > > - if (!qobj) { > + /* If there was an error, let the caller try and run into the error */ > + if (!qobj && !local_err) { > *present = false; > return; > } > > + error_free(local_err); > *present = true; > } > > @@ -820,6 +1015,7 @@ static void qobject_input_free(Visitor *v) > qobject_input_stack_object_free(tos); > } > > + qobject_unref(qiv->empty_qdict); > qobject_unref(qiv->root); > if (qiv->errname) { > g_string_free(qiv->errname, TRUE);