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 lists1p.gnu.org (lists1p.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 1F7A9C79FB6 for ; Wed, 9 Sep 2026 18:43:38 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1x4NGc-0002D9-HB; Wed, 09 Sep 2026 14:43:30 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1x4NGU-0002Ca-7X for qemu-devel@nongnu.org; Wed, 09 Sep 2026 14:43:22 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1x4NGR-0007z8-Ur for qemu-devel@nongnu.org; Wed, 09 Sep 2026 14:43:21 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1788979399; 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=bEqwXERtTnPz8AEnXPhlGtJhAmtZv1Zzr+R2za5hZ9U=; b=Q8wbCG4fTPf6Nremw7mrSz4RzCAKsDYXgiFsCMLF001FEMFn8UmMSZX9pduN2V/+yAUSRL 4vSuJTuSimj1xHrgQ60EFuFcNrbJtBKOz+RqoNv+4esD56cYy8hBcF6HOEim3jSegrJjTS rkaPafbHPeNdi3KDs/ewJJWtR9Mwooo= Received: from mx-prod-mc-05.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-112-Xi2pluZEPHOX3qgO-th7Kw-1; Wed, 09 Sep 2026 14:43:14 -0400 X-MC-Unique: Xi2pluZEPHOX3qgO-th7Kw-1 X-Mimecast-MFC-AGG-ID: Xi2pluZEPHOX3qgO-th7Kw_1788979393 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (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-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 59AF5195607F; Wed, 9 Sep 2026 18:43:13 +0000 (UTC) Received: from localhost (headnet04.pony-001.prod.iad2.dc.redhat.com [10.2.32.116]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id D7978180057E; Wed, 9 Sep 2026 18:43:12 +0000 (UTC) Date: Wed, 9 Sep 2026 14:43:11 -0400 From: Stefan Hajnoczi To: Niklas Cassel Cc: Kevin Wolf , Hanna Reitz , Sam Li , Damien Le Moal , qemu-block@nongnu.org, qemu-devel@nongnu.org Subject: Re: [PATCH v4 09/12] file-posix: base the zone append limit on the transfer limit Message-ID: <20260909184311.GI20134@fedora> References: <20260907110748.1868714-1-cassel@kernel.org> <20260907110748.1868714-10-cassel@kernel.org> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="hL9i6hWHbFBsxLJi" Content-Disposition: inline In-Reply-To: <20260907110748.1868714-10-cassel@kernel.org> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 Received-SPF: pass client-ip=170.10.133.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 12 X-Spam_score: 1.2 X-Spam_bar: + X-Spam_report: (1.2 / 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_SBL_CSS=3.335, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development 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 --hL9i6hWHbFBsxLJi Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Sep 07, 2026 at 01:07:44PM +0200, Niklas Cassel wrote: > The zone_append_max_bytes queue attribute is the largest > REQ_OP_ZONE_APPEND that the device accepts, and Linux has no interface > for issuing one from userspace: include/uapi has no such operation, and > every submitter of REQ_OP_ZONE_APPEND is in the kernel. Userspace writes > to a sequential zone with an ordinary write at the write pointer. >=20 > That is what this driver does. raw_co_zone_append() substitutes the write > pointer of the zone for the offset and hands the request to raw_co_prw(), > which reaches handle_aiocb_rw_vector() and issues a plain pwritev(). The > kernel never sees a zone append, so the attribute describes a limit on an > operation that is never issued. >=20 > Nor is it a limit that this driver runs into. The kernel splits a write > that exceeds the transfer limit rather than refusing it, so a larger > append succeeds: on a null_blk device whose zone_append_max_bytes is > 130560, a 16 MiB append completes and advances the write pointer by > 16 MiB. Reporting the attribute only understates what the driver can do, > because Linux derives it as a minimum that already includes max_sectors > and chunk_sectors. >=20 > Report max_hw_transfer instead, the limit that governs the write the > driver actually issues. There is no use in telling a guest that it may > append more than the device carries in one command, and a frontend then > does not have to reason about how this driver implements an append in > order to bound the value it advertises. >=20 > On a null_blk device with max_hw_sectors_kb of 127 and > zone_append_max_bytes of 130560, virtio-blk reports 255 sectors before > and after. >=20 > Reviewed-by: Damien Le Moal > Signed-off-by: Niklas Cassel > --- > block/file-posix.c | 13 +++++++++---- > 1 file changed, 9 insertions(+), 4 deletions(-) Reviewed-by: Stefan Hajnoczi --hL9i6hWHbFBsxLJi Content-Type: application/pgp-signature; name=signature.asc -----BEGIN PGP SIGNATURE----- iQEzBAEBCgAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmqhqL8ACgkQnKSrs4Gr c8joNQf/dOhQnxql/P3dHHV5DoYMJAEor0846zL4R48DGagZciG2m9TJCMwq87Am E6sgBROysTHS7SjHi5aOxPWyiLFlbw3xteMKb0PhBMw2gdfnaruCDDaE1igVD7kI Sp4m+AmCxddKQ548EQbeYbkDnz+QkiVBddq/vZ4yB2rU3EZTrQUDPiB3zCVlulxp 9nwBMGxbqPWJ53mO7dLwfH0Ypf4RW3ovzsEh7mKjd2Q9/1sct3NwMXifQuxEQ4/p ncbzSseyzY1fioeNQRsRFun+H2u1dEzF06Dv0e+MSKhJ+2/LcCYzJotgLEm9ZSQI f6nMUExpRTn3csOmfOtiQ5g6Zbss2A== =zIG9 -----END PGP SIGNATURE----- --hL9i6hWHbFBsxLJi--