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Re: [Qemu-devel] [RFC PATCH 0/7] virtio-fs: shared file system for virtu
From: |
Greg Kurz |
Subject: |
Re: [Qemu-devel] [RFC PATCH 0/7] virtio-fs: shared file system for virtual machines3 |
Date: |
Thu, 4 Apr 2019 15:24:54 +0200 |
On Mon, 10 Dec 2018 17:31:44 +0000
"Dr. David Alan Gilbert (git)" <address@hidden> wrote:
> From: "Dr. David Alan Gilbert" <address@hidden>
>
> Hi,
> This is the first RFC for the QEMU side of 'virtio-fs';
> a new mechanism for mounting host directories into the guest
> in a fast, consistent and secure manner. Our primary use
> case is kata containers, but it should be usable in other scenarios
> as well.
>
> There are corresponding patches being posted to Linux kernel,
> libfuse and kata lists.
>
> For a fuller design description, and benchmark numbers, please see
> Vivek's posting of the kernel set here:
>
> https://marc.info/?l=linux-kernel&m=154446243024251&w=2
>
> We've got a small website with instructions on how to use it, here:
>
> https://virtio-fs.gitlab.io/
>
> and all the code is available on gitlab at:
>
> https://gitlab.com/virtio-fs
>
Hi !
This looks like a very promising replacement for virtio-9p, at
least with better chances of reaching a production quality level.
Not sure I'll have enough time to step in, but please Cc me on
future posts. As virtio-9p maintainer, I'll be happy to help if
I can. Also I'll be happy to get rid of the fsdev proxy backend
at some point (which I already wanted to replace with a vhost
user based solution :-) ).
Cheers,
--
Greg
> QEMU's changes
> --------------
>
> The QEMU changes are pretty small;
>
> There's a new vhost-user device, which is used to carry a stream of
> FUSE messages to an external daemon that actually performs
> all the file IO. The FUSE daemon is an external process in order to
> achieve better isolation for security and resource control (e.g. number
> of file descriptors) and also because it's cleaner than trying to
> integrate libfuse into QEMU.
>
> This device has an extra BAR that contains (up to) 3 regions:
>
> a) a DAX mapping range ('the cache') - into which QEMU mmap's
> files on behalf of the external daemon; those files are
> then directly mapped by the guest in a way similar to a DAX
> backed file system; one advantage of this is that multiple
> guests all accessing the same files should all be sharing
> those pages of host cache.
>
> b) An experimental set of mappings for use by a metadata versioning
> daemon; this mapping is shared between multiple guests and
> the daemon, but only contains a set of version counters that
> allow a guest to quickly tell if its metadata is stale.
>
> TODO
> ----
>
> This is the first RFC, we know we have a bunch of things to clear up:
>
> a) The virtio device specificiation is still in flux and is expected
> to change
>
> b) We'd like to find ways of reducing the map/unmap latency for DAX
>
> c) The metadata versioning scheme needs to settle out.
>
> d) mmap'ing host files has some interesting side effects; for example
> if the file gets truncated by the host and then the guest accesses
> the mapping, KVM can fail the guest hard.
>
> Dr. David Alan Gilbert (6):
> virtio: Add shared memory capability
> virtio-fs: Add cache BAR
> virtio-fs: Add vhost-user slave commands for mapping
> virtio-fs: Fill in slave commands for mapping
> virtio-fs: Allow mapping of meta data version table
> virtio-fs: Allow mapping of journal
>
> Stefan Hajnoczi (1):
> virtio: add vhost-user-fs-pci device
>
> configure | 10 +
> contrib/libvhost-user/libvhost-user.h | 3 +
> docs/interop/vhost-user.txt | 35 ++
> hw/virtio/Makefile.objs | 1 +
> hw/virtio/vhost-user-fs.c | 517 ++++++++++++++++++++
> hw/virtio/vhost-user.c | 16 +
> hw/virtio/virtio-pci.c | 115 +++++
> hw/virtio/virtio-pci.h | 19 +
> include/hw/pci/pci.h | 1 +
> include/hw/virtio/vhost-user-fs.h | 79 +++
> include/standard-headers/linux/virtio_fs.h | 48 ++
> include/standard-headers/linux/virtio_ids.h | 1 +
> include/standard-headers/linux/virtio_pci.h | 9 +
> 13 files changed, 854 insertions(+)
> create mode 100644 hw/virtio/vhost-user-fs.c
> create mode 100644 include/hw/virtio/vhost-user-fs.h
> create mode 100644 include/standard-headers/linux/virtio_fs.h
>
- Re: [Qemu-devel] [RFC PATCH 0/7] virtio-fs: shared file system for virtual machines3,
Greg Kurz <=