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 8C92DC44501 for ; Tue, 7 Jul 2026 06:31:51 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wgzJO-00016K-Ou; Tue, 07 Jul 2026 02:29:42 -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 1wgzJL-000154-DE for qemu-devel@nongnu.org; Tue, 07 Jul 2026 02:29:39 -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 1wgzJJ-0006aO-IR for qemu-devel@nongnu.org; Tue, 07 Jul 2026 02:29:39 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1783405777; 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=tjbNF6RYtLwlGy7eCg9LgEfJgJ+JbZZyoXxcb8uVLPM=; b=XZcbaBoNsJOeB0Y+1+2tPsAd5xyQ4Jqrg8NmzqGMXA+Z2gEqGHGLaMwfRHYo4Tg3yh9D4V 1G0fxB09e1g8bvp++mU0a+bEVPOySP8SfDyYJc1Xm+HJC5QCo//rna7QGI85IQThv36kNd ZyRrW4QF7HCCSAW66a6V/E6EwyYzd44= 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-10-79i7G_h8Nym7ZGKDa6coPw-1; Tue, 07 Jul 2026 02:29:33 -0400 X-MC-Unique: 79i7G_h8Nym7ZGKDa6coPw-1 X-Mimecast-MFC-AGG-ID: 79i7G_h8Nym7ZGKDa6coPw_1783405772 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 722821955BFE; Tue, 7 Jul 2026 06:29:32 +0000 (UTC) Received: from corto.redhat.com (unknown [10.44.32.49]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 058E2180065F; Tue, 7 Jul 2026 06:29:30 +0000 (UTC) From: =?UTF-8?q?C=C3=A9dric=20Le=20Goater?= To: qemu-devel@nongnu.org Cc: Mattias Nissler , John Levon , =?UTF-8?q?C=C3=A9dric=20Le=20Goater?= Subject: [PULL 03/27] docs: Update vfio-user spec to describe DMA access mode bits Date: Tue, 7 Jul 2026 08:28:56 +0200 Message-ID: <20260707062920.317302-4-clg@redhat.com> In-Reply-To: <20260707062920.317302-1-clg@redhat.com> References: <20260707062920.317302-1-clg@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 Received-SPF: pass client-ip=170.10.133.124; envelope-from=clg@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 8 X-Spam_score: 0.8 X-Spam_bar: / X-Spam_report: (0.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.445, 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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_SBL_CSS=3.335, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001, TVD_PH_SUBJ_META1=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 From: Mattias Nissler This makes the intended access mode explicit when registering DMA regions with the server. A new "file I/O" access mode is defined, which can be used if the file descriptor provided by the client doesn't support `mmap()`. Signed-off-by: Mattias Nissler Reviewed-by: John Levon Link: https://lore.kernel.org/qemu-devel/20260602133829.305842-1-mnissler@meta.com Signed-off-by: Cédric Le Goater --- docs/interop/vfio-user.rst | 82 ++++++++++++++++++++++++-------------- 1 file changed, 51 insertions(+), 31 deletions(-) diff --git a/docs/interop/vfio-user.rst b/docs/interop/vfio-user.rst index 12deb25102af217f7f292b4cb655dc4a6a92439a..1c92f442d232ce6ce880868bb7062e42481b69ae 100644 --- a/docs/interop/vfio-user.rst +++ b/docs/interop/vfio-user.rst @@ -604,27 +604,31 @@ Request The request payload for this message is a structure of the following format: -+-------------+--------+-------------+ -| Name | Offset | Size | -+=============+========+=============+ -| argsz | 0 | 4 | -+-------------+--------+-------------+ -| flags | 4 | 4 | -+-------------+--------+-------------+ -| | +-----+------------+ | -| | | Bit | Definition | | -| | +=====+============+ | -| | | 0 | readable | | -| | +-----+------------+ | -| | | 1 | writeable | | -| | +-----+------------+ | -+-------------+--------+-------------+ -| offset | 8 | 8 | -+-------------+--------+-------------+ -| address | 16 | 8 | -+-------------+--------+-------------+ -| size | 24 | 8 | -+-------------+--------+-------------+ ++-------------+--------+------------------------+ +| Name | Offset | Size | ++=============+========+========================+ +| argsz | 0 | 4 | ++-------------+--------+------------------------+ +| flags | 4 | 4 | ++-------------+--------+------------------------+ +| | +-----+-----------------------+ | +| | | Bit | Definition | | +| | +=====+=======================+ | +| | | 0 | readable | | +| | +-----+-----------------------+ | +| | | 1 | writeable | | +| | +-----+-----------------------+ | +| | | 2 | access mode: mmap | | +| | +-----+-----------------------+ | +| | | 3 | access mode: file I/O | | +| | +-----+-----------------------+ | ++-------------+--------+------------------------+ +| offset | 8 | 8 | ++-------------+--------+------------------------+ +| address | 16 | 8 | ++-------------+--------+------------------------+ +| size | 24 | 8 | ++-------------+--------+------------------------+ * *argsz* is the size of the above structure. Note there is no reply payload, so this field differs from other message types. @@ -634,6 +638,8 @@ The request payload for this message is a structure of the following format: * *writeable* indicates that the region can be written to. + * *access mode* bits indicate how the region is to be accessed by the server. + * *offset* is the file offset of the region with respect to the associated file descriptor, or zero if the region is not mappable * *address* is the base DMA address of the region. @@ -641,16 +647,30 @@ The request payload for this message is a structure of the following format: This structure is 32 bytes in size, so the message size is 16 + 32 bytes. -If the DMA region being added can be directly mapped by the server, a file -descriptor must be sent as part of the message meta-data. The region can be -mapped via the mmap() system call. On ``AF_UNIX`` sockets, the file descriptor -must be passed as ``SCM_RIGHTS`` type ancillary data. Otherwise, if the DMA -region cannot be directly mapped by the server, no file descriptor must be sent -as part of the message meta-data and the DMA region can be accessed by the -server using ``VFIO_USER_DMA_READ`` and ``VFIO_USER_DMA_WRITE`` messages, -explained in `Read and Write Operations`_. A command to map over an existing -region must be failed by the server with ``EEXIST`` set in error field in the -reply. +There are several alternative access modes for the server to use when accessing +the region: + +* ``VFIO_USER_DMA_READ`` and ``VFIO_USER_DMA_WRITE`` messages, explained in + `Read and Write Operations`_. + +* ``mmap()`` a client-provided file descriptor, then perform direct accesses to + the underlying memory. + +* File I/O system calls (such as ``pread()`` / ``pwrite()``) against a + client-provided file descriptor. + +The access mode bits in the flags field indicate which access mode to use. If +an access mode requiring a file descriptor is specified, but the client does +not provide a file descriptor, the server must fail the request with +``EINVAL``. If no access mode flag bit is set, the server should use ``mmap()`` +based access if the client provided a file descriptor and message-based access +otherwise. + +On ``AF_UNIX`` sockets, the file descriptor must be passed as ``SCM_RIGHTS`` +type ancillary data. + +A command to map over an existing region must be failed by the server with +``EEXIST`` set in the error field in the reply. Reply ^^^^^ -- 2.54.0