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=-10.2 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 76CE7C433E0 for ; Fri, 12 Feb 2021 19:49:09 +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 D798964E02 for ; Fri, 12 Feb 2021 19:49:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D798964E02 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]:47348 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lAeR9-0000yN-Rp for qemu-devel@archiver.kernel.org; Fri, 12 Feb 2021 14:49:07 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:51636) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lAeMo-00076j-RJ for qemu-devel@nongnu.org; Fri, 12 Feb 2021 14:44:38 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:45038) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lAeMm-0006Ax-Nx for qemu-devel@nongnu.org; Fri, 12 Feb 2021 14:44:38 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1613159075; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=RQfcDJJCNsLHUbWKDd2jINmjvknOg/j8CsgUY9osG6Y=; b=Q71KvEZVvD5PegEcIa5jApNexafiT0E59A+0KW6qr2DUjhi4YAEw1ngz2pQODG2oHQR6Ck Rh9olqyF6LqyAeXN752+yRjfvHBt+iaq2McYpdAs+Ic1xYhKSiR4NWLXA8IDJHLDmUcry1 wJIbvccaMXuT8WwL8WhDZKVtjok/Zlg= 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-36-qIBUekLzPCW6Y_uIZkfzWg-1; Fri, 12 Feb 2021 14:44:28 -0500 X-MC-Unique: qIBUekLzPCW6Y_uIZkfzWg-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id B27D3107ACF2; Fri, 12 Feb 2021 19:44:25 +0000 (UTC) Received: from [10.3.114.150] (ovpn-114-150.phx2.redhat.com [10.3.114.150]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 14E3F60BE5; Fri, 12 Feb 2021 19:44:20 +0000 (UTC) To: Vladimir Sementsov-Ogievskiy , Alberto Garcia , qemu-block@nongnu.org References: <20210202124956.63146-1-vsementsov@virtuozzo.com> <20210202124956.63146-9-vsementsov@virtuozzo.com> From: Eric Blake Organization: Red Hat, Inc. Subject: Re: [PATCH v7 08/14] block/qcow2: qcow2_get_specific_info(): drop error propagation Message-ID: Date: Fri, 12 Feb 2021 13:44:19 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=eblake@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=eblake@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.569, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.119, 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=unavailable 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: kwolf@redhat.com, stefanha@redhat.com, qemu-devel@nongnu.org, armbru@redhat.com, pavel.dovgaluk@ispras.ru, pbonzini@redhat.com, mreitz@redhat.com, jsnow@redhat.com, ari@tuxera.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2/5/21 5:52 AM, Vladimir Sementsov-Ogievskiy wrote: > 05.02.2021 14:43, Alberto Garcia wrote: >> On Tue 02 Feb 2021 01:49:50 PM CET, Vladimir Sementsov-Ogievskiy wrote: >>> -Qcow2BitmapInfoList *qcow2_get_bitmap_info_list(BlockDriverState *bs, >>> -                                                Error **errp) >>> +bool qcow2_get_bitmap_info_list(BlockDriverState *bs, >>> +                                Qcow2BitmapInfoList **info_list, >>> Error **errp) >>>   { >>>       BDRVQcow2State *s = bs->opaque; >>>       Qcow2BitmapList *bm_list; >>>       Qcow2Bitmap *bm; >>> -    Qcow2BitmapInfoList *list = NULL; >>> -    Qcow2BitmapInfoList **tail = &list; >>>         if (s->nb_bitmaps == 0) { >>> -        return NULL; >>> +        *info_list = NULL; >>> +        return true; >>>       } >>>         bm_list = bitmap_list_load(bs, s->bitmap_directory_offset, >>>                                  s->bitmap_directory_size, errp); >>> -    if (bm_list == NULL) { >>> -        return NULL; >>> +    if (!bm_list) { >>> +        return false; >>>       } >>>   +    *info_list = NULL; >>> + >>>       QSIMPLEQ_FOREACH(bm, bm_list, entry) { >>>           Qcow2BitmapInfo *info = g_new0(Qcow2BitmapInfo, 1); >>>           info->granularity = 1U << bm->granularity_bits; >>>           info->name = g_strdup(bm->name); >>>           info->flags = get_bitmap_info_flags(bm->flags & >>> ~BME_RESERVED_FLAGS); >>> -        QAPI_LIST_APPEND(tail, info); >>> +        QAPI_LIST_APPEND(info_list, info); >>>       } >>>         bitmap_list_free(bm_list); >>>   -    return list; >>> +    return true; >>>   } >> >> Maybe I'm reading this wrong but... >> >> In the original code you had the head and tail of the list ('list' and >> 'tail') then you would append items to the tail and finally return the >> head. >> >> However the new code only uses and updates 'info_list' and it does not >> keep the head anywhere, so what the caller gets is a pointer to the >> tail. >> > > No. *info_list is modified only on the first loop iteration. And than > info_list is switched to &(*(info_list))->next, so on second iteration > we will modify @next field of first element, not original *info_list. Elsewhere when making these types of conversions, Markus suggested that I keep a separate tail variable, initialized by the parameter info_list, to make it more apparent. As in squashing the patch below: With that, it looks this series is reviewed, so I'm planning on taking it through my dirty-bitmaps tree (perhaps I'm stretching the fact that patch 10/14 is definitely dirty-bitmaps into taking the whole series, but I doubt I'll hear any complaints from other block maintainers) diff --git i/block/qcow2-bitmap.c w/block/qcow2-bitmap.c index e50da1ee7da3..f417f9ccb195 100644 --- i/block/qcow2-bitmap.c +++ w/block/qcow2-bitmap.c @@ -1103,6 +1103,7 @@ bool qcow2_get_bitmap_info_list(BlockDriverState *bs, BDRVQcow2State *s = bs->opaque; Qcow2BitmapList *bm_list; Qcow2Bitmap *bm; + Qcow2BitmapInfoList **tail; if (s->nb_bitmaps == 0) { *info_list = NULL; @@ -1116,13 +1117,14 @@ bool qcow2_get_bitmap_info_list(BlockDriverState *bs, } *info_list = NULL; + tail = info_list; QSIMPLEQ_FOREACH(bm, bm_list, entry) { Qcow2BitmapInfo *info = g_new0(Qcow2BitmapInfo, 1); info->granularity = 1U << bm->granularity_bits; info->name = g_strdup(bm->name); info->flags = get_bitmap_info_flags(bm->flags & ~BME_RESERVED_FLAGS); - QAPI_LIST_APPEND(info_list, info); + QAPI_LIST_APPEND(tail, info); } bitmap_list_free(bm_list); -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org