On Sat, Dec 22, 2018 at 05:27:28PM +0800, jiangyiwen wrote: > On 2018/12/11 1:31, Dr. David Alan Gilbert (git) wrote: > > From: "Dr. David Alan Gilbert" <dgilb...@redhat.com> > > > > 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 > > > > 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 > > > > Hi Dave, > > I encounter a problem after running qemu with virtio-fs, > > I find I only can mount virtio-fs using the following command: > mount -t virtio_fs /dev/null /mnt/virtio_fs/ -o > tag=myfs,rootmode=040000,user_id=0,group_id=0 > or mount -t virtio_fs /dev/null /mnt/virtio_fs/ -o > tag=myfs,rootmode=040000,user_id=0,group_id=0,dax > > Then, I want to know how to use "cache=always" or "cache=none", even > "cache=auto", "cache=writeback"? > > Thanks, > Yiwen.
Hi Yiwen, As of now, cache options are libfuse daemon options. So while starting daemon, specify "-o cache=none" or "-o cache=always" etc. One can not specify caching option at virtio-fs mount time. Thanks Vivek
