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 0FFE9D591AA for ; Mon, 18 Nov 2024 17:41:20 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1tD5kC-00088J-DB; Mon, 18 Nov 2024 12:41:01 -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 1tD5k8-00087C-U8 for qemu-devel@nongnu.org; Mon, 18 Nov 2024 12:40:56 -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 1tD5k7-0005Xp-8U for qemu-devel@nongnu.org; Mon, 18 Nov 2024 12:40:56 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1731951654; 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=UPebO9DOHT+/ZSSTHi4HkSIT8b97mrJIo/sLsV85sZ8=; b=Djxmbh7cjrhwHny2MsvSaFUiTiRp+0iwuYYveHcX3CdoYSi4rgiNrDCEvN4MsmQNjTQZVa wGIY9RAMtY73IWtQIXo4uhl/4DkdzVUr0jlJXhRNHT+dJdls4LGkSYWYF4IE7kN1QtRx31 2bY+pMhvTSX+M79+8IwtXkvMcmgEfqQ= Received: from mail-wm1-f72.google.com (mail-wm1-f72.google.com [209.85.128.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-637-VbryvYnhOSay0IdW-sZi_A-1; Mon, 18 Nov 2024 12:40:52 -0500 X-MC-Unique: VbryvYnhOSay0IdW-sZi_A-1 X-Mimecast-MFC-AGG-ID: VbryvYnhOSay0IdW-sZi_A Received: by mail-wm1-f72.google.com with SMTP id 5b1f17b1804b1-4315dd8fe7fso22566245e9.3 for ; Mon, 18 Nov 2024 09:40:51 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1731951651; x=1732556451; h=mime-version:message-id:date:references:in-reply-to:subject:cc:to :from:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=UPebO9DOHT+/ZSSTHi4HkSIT8b97mrJIo/sLsV85sZ8=; b=I27WLMkY/VMd8U4ORgQECOYPR9VjdbtjoHP8/GRLYZaHo0cQxwwkV/mDCbn1GJEzPV WCS+1w0RZMg1RtdACWEhRfFTso+fGG5W35SoiRucNPRrKJ/g3TpoQKPtyz+Kr+0dPuKo hGmsd0QBcNVNh8mn0asdpgnjUk4oXQHpP2TIsdjrcHrxcO14t+fkpoIw/l3q4CLBmy4g AzZFyKki66nbJGcgYsy4nxis4dF2vkkPeK5SZL4L4CX8491tNqSQa8tgYfJRaYCxW3vA aoaFynKUNOlcRwls9kN0aw9TJVVQ17QrCye6Z4SCV1ZM50JYrT/Qn38N04jSGyutGVuy YLzw== X-Gm-Message-State: AOJu0YxwpgXPu+61F0Uki1IKGG/+SEoukvi+vF/BnGKQmnKOqVFoum3A Onu01RdHv7RXkOQij+jrKcrsd4NcbjiOXZ+cqzA4fP3VBxKJf+LLaQrFZ+cofxgHtTTE29p+XiM XksSHBnEd0yvMwkpe1T2QJ+7qYIlXISdhQWb3foh/+11DE2TUZ+co X-Received: by 2002:a05:600c:5013:b0:431:4f29:9539 with SMTP id 5b1f17b1804b1-432df793ce7mr124788275e9.32.1731951651063; Mon, 18 Nov 2024 09:40:51 -0800 (PST) X-Google-Smtp-Source: AGHT+IH7GCvudkuP1haz122ydvMsndq4KxuYJ3F5hM/sh9uLdRiGfO0/MG46r8YMoIcyMYF2t5maiQ== X-Received: by 2002:a05:600c:5013:b0:431:4f29:9539 with SMTP id 5b1f17b1804b1-432df793ce7mr124788075e9.32.1731951650724; Mon, 18 Nov 2024 09:40:50 -0800 (PST) Received: from fedora ([85.119.46.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-432dab788a2sm161789735e9.11.2024.11.18.09.40.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 18 Nov 2024 09:40:50 -0800 (PST) From: Vitaly Kuznetsov To: Eric Blake Cc: qemu-devel@nongnu.org, Kevin Wolf , Hanna Reitz , qemu-block@nongnu.org Subject: Re: [PATCH v2] vpc: Read images exported from Azure correctly In-Reply-To: References: <20241118143646.33377-1-vkuznets@redhat.com> Date: Mon, 18 Nov 2024 18:40:48 +0100 Message-ID: <877c90qw2n.fsf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain Received-SPF: pass client-ip=170.10.129.124; envelope-from=vkuznets@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.142, 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_H2=-0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=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: 2.1.29 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 Eric Blake writes: > On Mon, Nov 18, 2024 at 03:36:46PM +0100, Vitaly Kuznetsov wrote: >> It was found that 'qemu-nbd' is not able to work with some disk images >> exported from Azure. Looking at the 512b footer (which contains VPC >> metadata): >> >> 00000000 63 6f 6e 65 63 74 69 78 00 00 00 02 00 01 00 00 |conectix........| >> 00000010 ff ff ff ff ff ff ff ff 2e c7 9b 96 77 61 00 00 |............wa..| >> 00000020 00 07 00 00 57 69 32 6b 00 00 00 01 40 00 00 00 |....Wi2k....@...| >> 00000030 00 00 00 01 40 00 00 00 28 a2 10 3f 00 00 00 02 |....@...(..?....| >> 00000040 ff ff e7 47 8c 54 df 94 bd 35 71 4c 94 5f e5 44 |...G.T...5qL._.D| >> 00000050 44 53 92 1a 00 00 00 00 00 00 00 00 00 00 00 00 |DS..............| >> 00000060 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| >> >> we can see that Azure uses a different 'Creator application' -- >> 'wa\0\0' (offset 0x1c, likely reads as 'Windows Azure') and QEMU uses this >> field to determine how it can get image size. Apparently, Azure uses 'new' >> method, just like Hyper-V. >> >> Signed-off-by: Vitaly Kuznetsov >> --- >> Alternatively, we can probably make 'current_size' the default and only use >> CHS for 'vpc '/'qemu'. >> --- >> block/vpc.c | 2 ++ >> 1 file changed, 2 insertions(+) >> >> diff --git a/block/vpc.c b/block/vpc.c >> index d95a204612b7..b67798697c15 100644 >> --- a/block/vpc.c >> +++ b/block/vpc.c >> @@ -321,6 +321,7 @@ static int vpc_open(BlockDriverState *bs, QDict *options, int flags, >> * 'qemu' : CHS QEMU (uses disk geometry) >> * 'qem2' : current_size QEMU (uses current_size) >> * 'win ' : current_size Hyper-V >> + * 'wa\0\0': current_size Azure >> * 'd2v ' : current_size Disk2vhd >> * 'tap\0' : current_size XenServer >> * 'CTXS' : current_size XenConverter >> @@ -330,6 +331,7 @@ static int vpc_open(BlockDriverState *bs, QDict *options, int flags, >> * that have CHS geometry of the maximum size. >> */ >> use_chs = (!!strncmp(footer->creator_app, "win ", 4) && >> + !!memcmp(footer->creator_app, "wa\0", 4) && > > While this is literally correct (a string literal with 3 characters > spelled out includes the implicit NUL byte; sizeof("wa\0") == 4), it > is a bit odd to see a memcmp() of 4 bytes against a literal containing > only 3 characters, especially when the comments above spelled it out > with four characters. For the sake of avoiding further confusion, it > might be nice to use memcmp() against explicit 4-byte patterns for all > of the strings (not just the Azure witness). Yea, it's just that we already have !!memcmp(footer->creator_app, "tap", 4)) down below so I decided to stick to the style :-) > >> !!strncmp(footer->creator_app, "qem2", 4) && >> !!strncmp(footer->creator_app, "d2v ", 4) && >> !!strncmp(footer->creator_app, "CTXS", 4) && > > I also don't know if it would be any easier to read by creating a > `static const char table[][4] = { "qemu", "qem2", "wa", ...}` (where > you don't have to write any explicit \0, because the compiler is > guaranteed to NUL-pad short strings into the char[4] table entry) and > then write a loop over each entry in the table, rather than having to > spell out a separate strncmp/memcmp line for each string in the table. I like the idea but I'm still trying to understand whether we need to keep adding new entries there or just flip the default and say that only 'vpc ' and 'qemu' are legacy and deserve CHS. -- Vitaly