From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 56628233722 for ; Wed, 22 Apr 2026 18:11:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776881474; cv=none; b=cHHn7YB699fK6XSFRKVQAuPgexhvjYGd5AkGgeUq+hJOPUACWZYQMsM+g0iKH37c2mp9g9DV2YNxhIMWrSq68qVz1gb4460XpGhbSCSSGrm9vYIhRSJfV73QQ1e/68LhedJ9y7Zin6HwJFL2V+/GYUISz91IMxTQChH0dtJ1psM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776881474; c=relaxed/simple; bh=QtDIqL7J6/LU2B0Y//ygFbtSoqYgYJZEHeVn2rm6swY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=pQ8kmQTqkcDySYFekwV+AJSXN9SDmxIGlZJ/8v8QVzu7btp6dvGZHhgqUGwWVFY3mBjLUl62zvTcbPU9B/VibtVCh1XrikNOEsRG81oyXTVu5YKC8RIB3Qy6Rx+KYmIdx/04obZkKCzXcswZRhmHYyhpjU2EVnl4Io5/cqgdo4s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=RtTJVb3V; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="RtTJVb3V" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1776881472; 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=/8NfjT5dajVkOm+K4KA/1uzKfa3Y5RoQPy90blWc6Zs=; b=RtTJVb3V580mD+xvJ6MuWjtdN7unfGD0tMJs8I6nKhiNNwflBjmKE7L/f0VkoQTNkq3oWn ezveGPpOd3eSCzoeKU//INfDNecYERV+3dX+HmXwQiM5xSKA07grXVAdT8zj7sT4FKjGhv Qqab5klopbBB78FOzmdP0tCvX0Lzfpc= 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-216-rxEsv59qP3GkzzHHjPw8_g-1; Wed, 22 Apr 2026 14:11:08 -0400 X-MC-Unique: rxEsv59qP3GkzzHHjPw8_g-1 X-Mimecast-MFC-AGG-ID: rxEsv59qP3GkzzHHjPw8_g_1776881467 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-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 115E91956061; Wed, 22 Apr 2026 18:11:07 +0000 (UTC) Received: from localhost (unknown [10.44.48.184]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 3594E180057E; Wed, 22 Apr 2026 18:11:05 +0000 (UTC) Date: Wed, 22 Apr 2026 14:11:04 -0400 From: Stefan Hajnoczi To: Matias Ezequiel Vara Larsen Cc: Demi Marie Obenour , virtio-comment Subject: Re: Max number of descriptors in a virtio-blk chain Message-ID: <20260422181104.GC498202@fedora> References: <8a7f186f-f240-4f58-a857-5900a2c0c217@gmail.com> Precedence: bulk X-Mailing-List: virtio-comment@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="3hmKfY5BbtmIx4pf" Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 --3hmKfY5BbtmIx4pf Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Apr 22, 2026 at 05:38:56PM +0200, Matias Ezequiel Vara Larsen wrote: > Hello, >=20 > On Wed, Apr 22, 2026 at 04:02:06AM -0400, Demi Marie Obenour wrote: > > Is there a limit to the number of descriptors that a virtio-blk driver > > can use in a request? In at least Cloud Hypervisor's implementation, >=20 > I think this is limited to the number of descriptors that you expose to > the device in the descriptor ring. In addition, I think the index is 16 > bits long. Virtqueue size is the upper limit. There are also additional Configuration Space fields that limit virtio-blk requests: - seg_max: max number of descriptors in a request - max_discard_seg: max number of descriptors for discard requests - max_write_zeroes_seg: max number of descriptors for write zeroes requests - max_secure_erase_seg: max number of descriptors for secure erase requests Stefan --3hmKfY5BbtmIx4pf Content-Type: application/pgp-signature; name=signature.asc -----BEGIN PGP SIGNATURE----- iQEyBAEBCgAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmnpDzgACgkQnKSrs4Gr c8h7UQf4yU369k0yIf5nt6EN/04pPMCCSSdgLeB4Tp891KkWhEd0E5pfUS9LU/uQ XTblTRaox4DSsMhmNiR59pL0SKUNqcN4nQ4Hiv1YSgALqrXGJ7N6NfZkz6fvj699 xAyeZZEBQs57VEsGXaQJV/3cG01JwSjfIXMVN3YYNpkOYDA+GvKikUyN587GU7T/ Ae7rIjUSqB9rGh/Ka0Ikvoh/dVcBP/rLibagJ0YsPxP275hPXNgDalr0t4fbiRMT pGjfONyjAcO7XPHHoxC9jVHnEEBzkLg7eaR3VdsUioeJOcn7hINeKpOtbZ/JmsZT qC29qFcndw0VN9EeL8CBuwT8uTjs =qwFJ -----END PGP SIGNATURE----- --3hmKfY5BbtmIx4pf--