On 2018/12/27 3:08, Vivek Goyal wrote: > 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 > > . >
Ok, I get it, thanks. Yiwen.
