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 B154CC47077 for ; Thu, 11 Jan 2024 11:46:00 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rNtVF-000859-BS; Thu, 11 Jan 2024 06:45:41 -0500 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 1rNtVC-00084f-Dv for qemu-devel@nongnu.org; Thu, 11 Jan 2024 06:45:38 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rNtV8-00070t-LP for qemu-devel@nongnu.org; Thu, 11 Jan 2024 06:45:37 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1704973533; 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=saFR7FAncgkLBqVR1h48nLPtt+cuwotjHAGNIVD1KQQ=; b=fKGdfpITJUHCeKnbnjNtCInVXPVLacHW/KE+UFljSkN8DusLH79QoDGVQDQROf+edpv0fX +2KPDamoL2OmgLvY4JQ3nHlQJ4rzsOxcMNsgrynEN0FijKbK+wkgfqc4vRiebuPn+thmB0 DlXz+E54OTzlMV9yGz8QctTn+Gxetao= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-645-NFTyCPu4O1GnNAWYQcRfcg-1; Thu, 11 Jan 2024 06:45:31 -0500 X-MC-Unique: NFTyCPu4O1GnNAWYQcRfcg-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 9CC4585A589; Thu, 11 Jan 2024 11:45:31 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.192.71]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 613D751D5; Thu, 11 Jan 2024 11:45:31 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 75C9E21E680D; Thu, 11 Jan 2024 12:45:30 +0100 (CET) From: Markus Armbruster To: Kevin Wolf Cc: qemu-block@nongnu.org, aliang@redhat.com, stefanha@redhat.com, qemu-devel@nongnu.org Subject: Re: [PATCH] string-output-visitor: Fix (pseudo) struct handling In-Reply-To: <20240109181717.42493-1-kwolf@redhat.com> (Kevin Wolf's message of "Tue, 9 Jan 2024 19:17:17 +0100") References: <20240109181717.42493-1-kwolf@redhat.com> Date: Thu, 11 Jan 2024 12:45:30 +0100 Message-ID: <87mstcxfdx.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.5 Received-SPF: pass client-ip=170.10.129.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -45 X-Spam_score: -4.6 X-Spam_bar: ---- X-Spam_report: (-4.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-2.467, 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, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-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 Kevin Wolf writes: > Commit ff32bb53 tried to get minimal struct support into the string > output visitor by just making it return "". Unfortunately, it > forgot that the caller will still make more visitor calls for the > content of the struct. > > If the struct is contained in a list, such as IOThreadVirtQueueMapping, > in the better case its fields show up as separate list entries. In the > worse case, it contains another list, and the string output visitor > doesn't support nested lists and asserts that this doesn't happen. What it actually asserts, or rather tries to assert is this constraint from visit_end_list()'s contract: * @list must match what was passed to the paired visit_start_list(). Since it's not prepared for nested lists, it actually asserts "match what was passed the last visit_start_list() for this visitor", which is correct only as long as there is no nesting. I'm not sure whether this is relevant enough to justify tweaking your commit message. > doesn't support nested lists and asserts that this doesn't happen. So as > soon as the optional "vqs" field in IOThreadVirtQueueMapping is > specified, we get a crash. > > This can be reproduced with the following command line: > > echo "info qtree" | ./qemu-system-x86_64 \ > -object iothread,id=t0 \ > -blockdev null-co,node-name=disk \ > -device '{"driver": "virtio-blk-pci", "drive": "disk", > "iothread-vq-mapping": [{"iothread": "t0", "vqs": [0]}]}' \ > -monitor stdio Appreciate the easy reproducer. > Fix the problem by counting the nesting level of structs and ignoring > any visitor calls for values (apart from start/end_struct) while we're > not on the top level. > > Fixes: ff32bb53476539d352653f4ed56372dced73a388 > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2069 > Reported-by: Aihua Liang > Signed-off-by: Kevin Wolf > --- > qapi/string-output-visitor.c | 46 ++++++++++++++++++++++++++++++++++++ > 1 file changed, 46 insertions(+) > > diff --git a/qapi/string-output-visitor.c b/qapi/string-output-visitor.c > index f0c1dea89e..5115536b15 100644 > --- a/qapi/string-output-visitor.c > +++ b/qapi/string-output-visitor.c > @@ -65,6 +65,7 @@ struct StringOutputVisitor > } range_start, range_end; > GList *ranges; > void *list; /* Only needed for sanity checking the caller */ > + unsigned int struct_nesting; > }; > > static StringOutputVisitor *to_sov(Visitor *v) > @@ -144,6 +145,10 @@ static bool print_type_int64(Visitor *v, const char *name, int64_t *obj, > StringOutputVisitor *sov = to_sov(v); > GList *l; > > + if (sov->struct_nesting) { > + return true; > + } > + > switch (sov->list_mode) { > case LM_NONE: > string_output_append(sov, *obj); > @@ -231,6 +236,10 @@ static bool print_type_size(Visitor *v, const char *name, uint64_t *obj, > uint64_t val; > char *out, *psize; > > + if (sov->struct_nesting) { > + return true; > + } > + > if (!sov->human) { > out = g_strdup_printf("%"PRIu64, *obj); > string_output_set(sov, out); > @@ -250,6 +259,11 @@ static bool print_type_bool(Visitor *v, const char *name, bool *obj, > Error **errp) > { > StringOutputVisitor *sov = to_sov(v); > + > + if (sov->struct_nesting) { > + return true; > + } > + > string_output_set(sov, g_strdup(*obj ? "true" : "false")); > return true; > } > @@ -260,6 +274,10 @@ static bool print_type_str(Visitor *v, const char *name, char **obj, > StringOutputVisitor *sov = to_sov(v); > char *out; > > + if (sov->struct_nesting) { > + return true; > + } > + > if (sov->human) { > out = *obj ? g_strdup_printf("\"%s\"", *obj) : g_strdup(""); > } else { > @@ -273,6 +291,11 @@ static bool print_type_number(Visitor *v, const char *name, double *obj, > Error **errp) > { > StringOutputVisitor *sov = to_sov(v); > + > + if (sov->struct_nesting) { > + return true; > + } > + > string_output_set(sov, g_strdup_printf("%.17g", *obj)); > return true; > } > @@ -283,6 +306,10 @@ static bool print_type_null(Visitor *v, const char *name, QNull **obj, > StringOutputVisitor *sov = to_sov(v); > char *out; > > + if (sov->struct_nesting) { > + return true; > + } > + > if (sov->human) { > out = g_strdup(""); > } else { > @@ -295,6 +322,9 @@ static bool print_type_null(Visitor *v, const char *name, QNull **obj, > static bool start_struct(Visitor *v, const char *name, void **obj, > size_t size, Error **errp) > { > + StringOutputVisitor *sov = to_sov(v); > + > + sov->struct_nesting++; > return true; > } > > @@ -302,6 +332,10 @@ static void end_struct(Visitor *v, void **obj) > { > StringOutputVisitor *sov = to_sov(v); > > + if (--sov->struct_nesting) { > + return; > + } > + > /* TODO actually print struct fields */ > string_output_set(sov, g_strdup("")); > } > @@ -312,6 +346,10 @@ start_list(Visitor *v, const char *name, GenericList **list, size_t size, > { > StringOutputVisitor *sov = to_sov(v); > > + if (sov->struct_nesting) { > + return true; > + } > + > /* we can't traverse a list in a list */ > assert(sov->list_mode == LM_NONE); > /* We don't support visits without a list */ > @@ -329,6 +367,10 @@ static GenericList *next_list(Visitor *v, GenericList *tail, size_t size) > StringOutputVisitor *sov = to_sov(v); > GenericList *ret = tail->next; > > + if (sov->struct_nesting) { > + return ret; > + } > + > if (ret && !ret->next) { > sov->list_mode = LM_END; > } > @@ -339,6 +381,10 @@ static void end_list(Visitor *v, void **obj) > { > StringOutputVisitor *sov = to_sov(v); > > + if (sov->struct_nesting) { > + return; > + } > + > assert(sov->list == obj); > assert(sov->list_mode == LM_STARTED || > sov->list_mode == LM_END || @struct_nesting is what its name suggests: the *struct* nesting level. The patch's idea is to turn all methods into no-ops inside a struct. To make that work, start_struct() and end_struct() aren't actually no-ops; they track the nesting level. What about nested lists that are not inside any struct? Ceterum censeo: the struct visitors need to go. But I'm *not* asking you to do that now.