From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; t=1684338768; x=1686930768; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:user-agent:from:to:cc:subject:date:message-id:reply-to; bh=2zgawbbiH3ZN+t5cl5i5se7wIX3B/JzZA+6PRyvIIdQ=; b=g5vI9spJJGk0AQg2nrDscgqmqP0hfliUsHdlmHIo3Us/3MCHru8MSL5VhuY5GT2/mq dRoS9rGKH+DSY0Pk6SGac+3nIrPcqrixW/J4kbvJqqzBVSCbZ8xOFTu/ib1xQ7zviDZk ibs2kc+8BOqHSss7aGDvVd5cDpfR14sdXJxylUPWqT/o/PqQ4hY9XSf+wHEmCaQh4q94 FdFDSJGxvGseU3ZcQCFrHKeAwnWn++N0N3NhMWfDwCBhXlwgBEWuTh1Zzuy6AvkocsEa JF4hTrpK1NZCFMuLudbaFaQY4XnlK7TfXMkMNOZzzhktmkAMiz6g0Gc46Sl6Jd0zwx3/ nMSQ== From: Alex =?utf-8?Q?Benn=C3=A9e?= Date: Wed, 17 May 2023 16:23:46 +0100 Message-ID: <87v8grlzu9.fsf@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Subject: [Virtio-fs] Status of DAX for virtio-fs/virtiofsd? List-Id: Development discussions about virtio-fs List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: QEMU Developers Cc: Stefan Hajnoczi , virtio-fs@redhat.com, Erik Schilling Hi, I remember from the dim and distant past (probably a KVM Forum) that one of the touted features of virtio-fs was the ability to get memory efficiency savings by having a direct memory mapping the host pages into the guest address space. AFAICT the kernel side was merged a while ago, see 22f3787 (virtiofs: set up virtio_fs dax_device) and related. However when investigating what would be needed to support this for Xen guests using virtio-fs we were confused as to what else was needed. There were some patches for the old C daemon: Subject: [PATCH v3 00/26] virtiofs dax patches Date: Wed, 28 Apr 2021 12:00:34 +0100=09[thread overview] Message-ID: <20210428110100.27757-1-dgilbert@redhat.com> although they look like they were never merged and the C version of virtiofsd has since been dropped from tools. Looking at the supporting rust code (vhost_user/message.rs) there are a number of additional messages: /// Virtio-fs draft: map file content into the window. FS_MAP =3D 6, /// Virtio-fs draft: unmap file content from the window. FS_UNMAP =3D 7, /// Virtio-fs draft: sync file content. FS_SYNC =3D 8, /// Virtio-fs draft: perform a read/write from an fd directly to GPA. FS_IO =3D 9, /// Upper bound of valid commands. MAX_CMD =3D 10, that don't appear in the current canonical vhost-user reference in the QEMU repository and the QEMU code certainly doesn't have implementations for any of them. So I have some questions: * What VMM/daemon combinations has DAX been tested on? * Isn't it time the vhost-user spec is updated? * Is anyone picking up Dave's patches for the QEMU side of support? Thanks, --=20 Alex Benn=C3=A9e Virtualisation Tech Lead @ Linaro