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 E2B22CCFA13 for ; Mon, 10 Nov 2025 15:22:58 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1vITiT-0003uK-EC; Mon, 10 Nov 2025 10:22:01 -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 1vIThe-0003Wx-P1 for qemu-devel@nongnu.org; Mon, 10 Nov 2025 10:21:15 -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 1vIThX-0004ti-M1 for qemu-devel@nongnu.org; Mon, 10 Nov 2025 10:21:09 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1762788061; 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=3k+rLrnrlSkofEu1Jhi8CHWFopk0vbU9Y9WKrdnwfzM=; b=aNN0RC7VFAyz4Ir1KFaRxqIy5GqTxxYHACj/M7qnyqr9UvLUp8G/Tt0vbww9SZhEbS2GKZ lReMgb864VfqkxeW0aX9dEo6a0KnljL35TuG4Wi34C7oZYq/ucMdI3cHb05FKyJoX+FzbB ww5Ds18xrNWchvm7+M9mrDEzRQLwV4M= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-373-s0GvmK4ENmahmVyPPCu8UQ-1; Mon, 10 Nov 2025 10:20:58 -0500 X-MC-Unique: s0GvmK4ENmahmVyPPCu8UQ-1 X-Mimecast-MFC-AGG-ID: s0GvmK4ENmahmVyPPCu8UQ_1762788057 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (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 mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 8911F193E8B7; Mon, 10 Nov 2025 15:20:57 +0000 (UTC) Received: from redhat.com (unknown [10.44.33.209]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 18F671800451; Mon, 10 Nov 2025 15:20:54 +0000 (UTC) Date: Mon, 10 Nov 2025 16:20:52 +0100 From: Kevin Wolf To: Markus Armbruster Cc: =?iso-8859-1?Q?Cl=E9ment?= Chigot , qemu-block@nongnu.org, qemu-devel@nongnu.org, hreitz@redhat.com, eblake@redhat.com Subject: Re: [PATCH v2 5/5] vvfat: add support for "fat-size" options Message-ID: References: <20251107145327.539481-1-chigot@adacore.com> <20251107145327.539481-6-chigot@adacore.com> <87zf8umbzh.fsf@pond.sub.org> <87bjlakpa5.fsf@pond.sub.org> <87o6paj96k.fsf@pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <87o6paj96k.fsf@pond.sub.org> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 Received-SPF: pass client-ip=170.10.129.124; envelope-from=kwolf@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, 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_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_PASS=-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 Am 10.11.2025 um 14:42 hat Markus Armbruster geschrieben: > Clément Chigot writes: > > > On Mon, Nov 10, 2025 at 2:09 PM Markus Armbruster wrote: > >> > >> Clément Chigot writes: > >> > >> > On Mon, Nov 10, 2025 at 11:13 AM Markus Armbruster wrote: > >> >> > >> >> Clément Chigot writes: > >> >> > >> >> > This allows more flexibility to vvfat backend. The values of "Number of > >> >> > Heads" and "Sectors per track" are based on SD specifications Part 2. > >> >> > > >> >> > Due to the FAT architecture, not all sizes are reachable. Therefore, it > >> >> > could be round up to the closest available size. > >> >> > > >> >> > FAT32 has not been adjusted and thus still default to 504 Mib. > >> >> > > >> >> > For floppy, only 1440 Kib and 2880 Kib are supported. > >> >> > > >> >> > Signed-off-by: Clément Chigot > >> >> > >> >> [...] > >> >> > >> >> > diff --git a/qapi/block-core.json b/qapi/block-core.json > >> >> > index 8a479ba090..0bcb360320 100644 > >> >> > --- a/qapi/block-core.json > >> >> > +++ b/qapi/block-core.json > >> >> > @@ -3478,11 +3478,17 @@ > >> >> > # (default: true) > >> >> > # (since 10.2) > >> >> > # > >> >> > +# @fat-size: size of the device in bytes. Due to FAT underlying > >> >> > +# architecture, this size can be rounded up to the closest valid > >> >> > +# size. > >> >> > +# (since 10.2) > >> >> > +# > >> >> > >> >> Can you explain again why you moved from @size to @fat-size? > >> > > >> > Just to be sure, you mean in the above comment, in the commit message or both ? > >> > >> Just to me, because I'm not sure I like the change, but that may well be > >> due to a lack of understanding of your reasons. > > > > Naming `fat-size` instead of `size` ensures the parameter is only > > recognized by the vvfat backend. In particular, it will be refused by > > the default raw format, avoiding confusion: > > "-drive file=fat:,size=256M" results in a 504M FAT disk > > truncated to 256M, raw format being implicit. > > "-drive file=fat:,fat-size=256M" is refused. "fat-size" is > > unsupported by raw format. > > I figure throwing in format=raw to make raw format explicit doesn't > change anything. Correct? > > > "-drive file=fat:,format=vvfat,fat-size=256M" results in a 256M FAT disk. > > "-drive file=fat:,format=vvfat,size=256M" is refused. "size" is > > unsupported by vvfat format. > > If it was called @size, what behavior would we get? Just two cases, I > think: > > 1. With raw format: > > -drive file=fat:,size=256M You'd silently get a 504 MiB filesystem truncated to 256 MiB (i.e. a corrupted file system). It's quite easy to forget format=vvfat, so something that initially looks like it might be working is not a great result for this user error. > 2. Without raw format: > > -drive file=fat:,format=vvfat,size=256M This does the thing that you actually want, a 256 MiB file system. I suggested to rename the vvfat option in v1 to make accidents at least a bit less likely. I'm not completely sure if "fat-size" is the best name, though, as it sounds as if it referred to the FAT itself instead of the FAT filesystem. Maybe "fs-size"? Kevin