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[212.96.48.140]) by smtp.gmail.com with ESMTPSA id g185sm12803wme.10.2019.09.10.08.12.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 10 Sep 2019 08:12:13 -0700 (PDT) From: Miklos Szeredi To: virtualization@lists.linux-foundation.org, linux-fsdevel@vger.kernel.org Cc: Stefan Hajnoczi , linux-kernel@vger.kernel.org, "Michael S. Tsirkin" , Vivek Goyal , "Dr. David Alan Gilbert" Subject: [PATCH v5 3/4] virtio-fs: add Documentation/filesystems/virtiofs.rst Date: Tue, 10 Sep 2019 17:12:05 +0200 Message-Id: <20190910151206.4671-4-mszeredi@redhat.com> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190910151206.4671-1-mszeredi@redhat.com> References: <20190910151206.4671-1-mszeredi@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Stefan Hajnoczi Add information about the new "virtiofs" file system. Signed-off-by: Stefan Hajnoczi Signed-off-by: Miklos Szeredi --- Documentation/filesystems/index.rst | 10 +++++ Documentation/filesystems/virtiofs.rst | 60 ++++++++++++++++++++++++++ MAINTAINERS | 11 +++++ 3 files changed, 81 insertions(+) create mode 100644 Documentation/filesystems/virtiofs.rst diff --git a/Documentation/filesystems/index.rst b/Documentation/filesystems/index.rst index 2de2fe2ab078..56e94bfc580f 100644 --- a/Documentation/filesystems/index.rst +++ b/Documentation/filesystems/index.rst @@ -32,3 +32,13 @@ filesystem implementations. journalling fscrypt + +Filesystems +=========== + +Documentation for filesystem implementations. + +.. toctree:: + :maxdepth: 2 + + virtiofs diff --git a/Documentation/filesystems/virtiofs.rst b/Documentation/filesystems/virtiofs.rst new file mode 100644 index 000000000000..4f338e3cb3f7 --- /dev/null +++ b/Documentation/filesystems/virtiofs.rst @@ -0,0 +1,60 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=================================================== +virtiofs: virtio-fs host<->guest shared file system +=================================================== + +- Copyright (C) 2019 Red Hat, Inc. + +Introduction +============ +The virtiofs file system for Linux implements a driver for the paravirtualized +VIRTIO "virtio-fs" device for guest<->host file system sharing. It allows a +guest to mount a directory that has been exported on the host. + +Guests often require access to files residing on the host or remote systems. +Use cases include making files available to new guests during installation, +booting from a root file system located on the host, persistent storage for +stateless or ephemeral guests, and sharing a directory between guests. + +Although it is possible to use existing network file systems for some of these +tasks, they require configuration steps that are hard to automate and they +expose the storage network to the guest. The virtio-fs device was designed to +solve these problems by providing file system access without networking. + +Furthermore the virtio-fs device takes advantage of the co-location of the +guest and host to increase performance and provide semantics that are not +possible with network file systems. + +Usage +===== +Mount file system with tag ``myfs`` on ``/mnt``: + +.. code-block:: sh + + guest# mount -t virtiofs myfs /mnt + +Please see https://virtio-fs.gitlab.io/ for details on how to configure QEMU +and the virtiofsd daemon. + +Internals +========= +Since the virtio-fs device uses the FUSE protocol for file system requests, the +virtiofs file system for Linux is integrated closely with the FUSE file system +client. The guest acts as the FUSE client while the host acts as the FUSE +server. The /dev/fuse interface between the kernel and userspace is replaced +with the virtio-fs device interface. + +FUSE requests are placed into a virtqueue and processed by the host. The +response portion of the buffer is filled in by the host and the guest handles +the request completion. + +Mapping /dev/fuse to virtqueues requires solving differences in semantics +between /dev/fuse and virtqueues. Each time the /dev/fuse device is read, the +FUSE client may choose which request to transfer, making it possible to +prioritize certain requests over others. Virtqueues have queue semantics and +it is not possible to change the order of requests that have been enqueued. +This is especially important if the virtqueue becomes full since it is then +impossible to add high priority requests. In order to address this difference, +the virtio-fs device uses a "hiprio" virtqueue specifically for requests that +have priority over normal requests. diff --git a/MAINTAINERS b/MAINTAINERS index 9cbcf167bdd0..459b3fa8e25e 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -17117,6 +17117,17 @@ S: Supported F: drivers/s390/virtio/ F: arch/s390/include/uapi/asm/virtio-ccw.h +VIRTIO FILE SYSTEM +M: Stefan Hajnoczi +M: Miklos Szeredi +L: virtualization@lists.linux-foundation.org +L: linux-fsdevel@vger.kernel.org +W: https://virtio-fs.gitlab.io/ +S: Supported +F: fs/fuse/virtio_fs.c +F: include/uapi/linux/virtio_fs.h +F: Documentation/filesystems/virtiofs.rst + VIRTIO GPU DRIVER M: David Airlie M: Gerd Hoffmann -- 2.21.0