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 AA235CCFA1A for ; Wed, 12 Nov 2025 12:59:45 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1vJAQz-0000Y5-4I; Wed, 12 Nov 2025 07:58:49 -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 1vJ9yf-0000j4-P0 for qemu-devel@nongnu.org; Wed, 12 Nov 2025 07:29:36 -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 1vJ9yc-0005eM-QG for qemu-devel@nongnu.org; Wed, 12 Nov 2025 07:29:32 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1762950570; 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=Xpzpb6IL2uF0SKnJ5KNKUpb4zHYen66jHpsBN/CbHOw=; b=ENj8CqTQulEShAYJPIWzflFwj+RsULx79cdoOh0y6rT/Dc2E9ditHpwChh5FGRtAUXGDeV g95GVciTqY4kHQOJqmaq69ktp08bWoz+vUGFKtC600aAmY/pbqg3faR0+JkklJhSynDn0A FzVU6WZnZCUk8ctPiTslQ8fUXHMu5mg= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-631-df0m1b7XMmiifnmfZ64VFA-1; Wed, 12 Nov 2025 07:29:24 -0500 X-MC-Unique: df0m1b7XMmiifnmfZ64VFA-1 X-Mimecast-MFC-AGG-ID: df0m1b7XMmiifnmfZ64VFA_1762950564 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (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-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 93313180049F; Wed, 12 Nov 2025 12:29:23 +0000 (UTC) Received: from redhat.com (unknown [10.44.33.98]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 94D0119560A2; Wed, 12 Nov 2025 12:29:20 +0000 (UTC) Date: Wed, 12 Nov 2025 13:29:17 +0100 From: Kevin Wolf To: =?iso-8859-1?Q?Cl=E9ment?= Chigot Cc: BALATON Zoltan , Markus Armbruster , 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: <20251107145327.539481-6-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: X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 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, 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_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 12.11.2025 um 10:50 hat Clément Chigot geschrieben: > On Mon, Nov 10, 2025 at 5:31 PM Kevin Wolf wrote: > > > > Am 10.11.2025 um 16:36 hat BALATON Zoltan geschrieben: > > > On Mon, 10 Nov 2025, Kevin Wolf wrote: > > > > 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. > > > > > > Why doesn't file=fat: imply format=vvfat? For what is the fat: part in > > > file then? > > > > -drive is built pretty much on the assumption that you have an image > > format that runs on top of a protocol. Format probing probes the image > > format, not the protocol, while prefixes like fat: (or nbd:, http: etc.) > > specify the protocol. > > > > So if you don't specify the format, we first open the protocol level > > (which is vvfat) and then probing will detect that over this protocol, > > we access a raw image. So it's mostly like saying format=raw. > > > > I think that format= works is really more accidental, > > but we can't change it now (and probably also don't want to). It results > > in opening only the protocol layer and not stacking any format driver on > > top of it. > > > > Options that you specify in -drive generally go to the top layer. So the > > consequence in our case is that with format=vvfat, the option goes to > > vvfat, but with format=raw (or unspecified format), it goes to the raw > > forma driver. > > > > > I currently recommend using: > > > > > > -drive if=none,id=ufat,format=raw,file=fat:rw:/dir/to/export > > > -device usb-storage,drive=ufat > > > > > > to my users which I got from somewhere but don't remember where and it > > > seems to work but maybe not the best way to specify this. > > > > It's fine, and I might use the same one myself (though you should be > > aware that fat:rw: is risky, it's full of bugs). > > > > But if you add an option like size=64M, it goes to the raw driver, which > > will take whatever image you access on the protocol level and truncate > > it at 64 MiB. > > > > If you want to give the size option on the vvfat level (and create a > > filesystem that is actually only 64 MiB instead of truncating a larger > > one), then obviously format=vvfat allows you to do that because then > > there is no raw format layer to begin with. Or if you do have the raw > > format layer, you can access options of the protocol layer by prefixing > > "file.". So format=raw,file.size=64M would still pass the size option to > > vvfat. > > How is `file.size` working ? I've tried a similar syntax for other > vvfat options (e.g `file.floppy` or the new `file.partitioned`) but > those have no effect. Is this because there are fetched within the > "filename" > Wondering because I'mn ot a fan of the new ":unpartitioned:", I've > added in patch 1. If it can simply be replaced by > `format=raw,file.partitioned=false` or > `format=vvfat,partitioned=false`. I think that would be far enough for > its purpose. Yes, I think it's because vvfat_parse_filename() overwrites them unconditionally while getting the options from the filename. Kevin