Hi, Here are the RFC patches for V2 of virtio-fs. These patches apply on top of 5.1 kernel. These patches are also available here. https://github.com/rhvgoyal/linux/commits/virtio-fs-dev-5.1 Patches for V1 were posted here. https://lwn.net/ml/linux-fsdevel/20181210171318.16998-1-vgoyal@xxxxxxxxxx/ This is still work in progress. As of now one can passthrough a host directory in to guest and it works reasonably well. pjdfstests test suite passes and blogbench runs. But this dirctory can't be shared between guests and host can't modify files in directory yet. That's still TBD. Posting another version to gather feedback and comments on progress so far. More information about the project can be found here. https://virtio-fs.gitlab.io/ Changes from V1 =============== - Various bug fixes - virtio-fs dax huge page size working, leading to improved performance. - Fixed kernel automated tests warnings. - Better handling of shared cache region reporting by virtio device. Description from V1 posting --------------------------- Problem Description =================== We want to be able to take a directory tree on the host and share it with guest[s]. Our goal is to be able to do it in a fast, consistent and secure manner. Our primary use case is kata containers, but it should be usable in other scenarios as well. Containers may rely on local file system semantics for shared volumes, read-write mounts that multiple containers access simultaneously. File system changes must be visible to other containers with the same consistency expected of a local file system, including mmap MAP_SHARED. Existing Solutions ================== We looked at existing solutions and virtio-9p already provides basic shared file system functionality although does not offer local file system semantics, causing some workloads and test suites to fail. In addition, virtio-9p performance has been an issue for Kata Containers and we believe this cannot be alleviated without major changes that do not fit into the 9P protocol. Design Overview =============== With the goal of designing something with better performance and local file system semantics, a bunch of ideas were proposed. - Use fuse protocol (instead of 9p) for communication between guest and host. Guest kernel will be fuse client and a fuse server will run on host to serve the requests. Benchmark results are encouraging and show this approach performs well (2x to 8x improvement depending on test being run). - For data access inside guest, mmap portion of file in QEMU address space and guest accesses this memory using dax. That way guest page cache is bypassed and there is only one copy of data (on host). This will also enable mmap(MAP_SHARED) between guests. - For metadata coherency, there is a shared memory region which contains version number associated with metadata and any guest changing metadata updates version number and other guests refresh metadata on next access. This is yet to be implemented. How virtio-fs differs from existing approaches ============================================== The unique idea behind virtio-fs is to take advantage of the co-location of the virtual machine and hypervisor to avoid communication (vmexits). DAX allows file contents to be accessed without communication with the hypervisor. The shared memory region for metadata avoids communication in the common case where metadata is unchanged. By replacing expensive communication with cheaper shared memory accesses, we expect to achieve better performance than approaches based on network file system protocols. In addition, this also makes it easier to achieve local file system semantics (coherency). These techniques are not applicable to network file system protocols since the communications channel is bypassed by taking advantage of shared memory on a local machine. This is why we decided to build virtio-fs rather than focus on 9P or NFS. HOWTO ====== We have put instructions on how to use it here. https://virtio-fs.gitlab.io/ Caching Modes ============= Like virtio-9p, different caching modes are supported which determine the coherency level as well. The “cache=FOO” and “writeback” options control the level of coherence between the guest and host filesystems. The “shared” option only has an effect on coherence between virtio-fs filesystem instances running inside different guests. - cache=none metadata, data and pathname lookup are not cached in guest. They are always fetched from host and any changes are immediately pushed to host. - cache=always metadata, data and pathname lookup are cached in guest and never expire. - cache=auto metadata and pathname lookup cache expires after a configured amount of time (default is 1 second). Data is cached while the file is open (close to open consistency). - writeback/no_writeback These options control the writeback strategy. If writeback is disabled, then normal writes will immediately be synchronized with the host fs. If writeback is enabled, then writes may be cached in the guest until the file is closed or an fsync(2) performed. This option has no effect on mmap-ed writes or writes going through the DAX mechanism. - shared/no_shared These options control the use of the shared version table. If shared mode is enabled then metadata and pathname lookup is cached in guest, but is refreshed due to changes in another virtio-fs instance. DAX === - dax can be turned on/off when mounting virtio-fs inside guest. TODO ==== - Implement "cache=shared" option. - Improve error handling on host. If page fault on host fails, we need to propagate it into guest. - Try to fine tune for performance. - Bug fixes RESULTS ======= - pjdfstests are passing. Have tried cache=none/auto/always and dax on/off). https://github.com/pjd/pjdfstest (one symlink test fails and that seems to be due xfs on host. Yet to look into it). - Ran blogbench and that works too. Thanks Vivek Miklos Szeredi (2): fuse: delete dentry if timeout is zero fuse: Use default_file_splice_read for direct IO Sebastien Boeuf (3): virtio: Add get_shm_region method virtio: Implement get_shm_region for PCI transport virtio: Implement get_shm_region for MMIO transport Stefan Hajnoczi (10): fuse: export fuse_end_request() fuse: export fuse_len_args() fuse: export fuse_get_unique() fuse: extract fuse_fill_super_common() fuse: add fuse_iqueue_ops callbacks virtio_fs: add skeleton virtio_fs.ko module dax: remove block device dependencies fuse, dax: add fuse_conn->dax_dev field virtio_fs, dax: Set up virtio_fs dax_device fuse, dax: add DAX mmap support Vivek Goyal (15): fuse: Clear setuid bit even in cache=never path fuse: Export fuse_send_init_request() fuse: Separate fuse device allocation and installation in fuse_conn dax: Pass dax_dev to dax_writeback_mapping_range() fuse: Keep a list of free dax memory ranges fuse: Introduce setupmapping/removemapping commands fuse, dax: Implement dax read/write operations fuse: Define dax address space operations fuse, dax: Take ->i_mmap_sem lock during dax page fault fuse: Maintain a list of busy elements fuse: Add logic to free up a memory range fuse: Release file in process context fuse: Reschedule dax free work if too many EAGAIN attempts fuse: Take inode lock for dax inode truncation virtio-fs: Do not provide abort interface in fusectl drivers/dax/super.c | 3 +- drivers/virtio/virtio_mmio.c | 32 + drivers/virtio/virtio_pci_modern.c | 108 +++ fs/dax.c | 23 +- fs/ext2/inode.c | 2 +- fs/ext4/inode.c | 2 +- fs/fuse/Kconfig | 11 + fs/fuse/Makefile | 1 + fs/fuse/control.c | 4 +- fs/fuse/cuse.c | 5 +- fs/fuse/dev.c | 80 +- fs/fuse/dir.c | 28 +- fs/fuse/file.c | 953 ++++++++++++++++++++++- fs/fuse/fuse_i.h | 206 ++++- fs/fuse/inode.c | 307 ++++++-- fs/fuse/virtio_fs.c | 1129 ++++++++++++++++++++++++++++ fs/splice.c | 3 +- fs/xfs/xfs_aops.c | 2 +- include/linux/dax.h | 6 +- include/linux/fs.h | 2 + include/linux/virtio_config.h | 17 + include/uapi/linux/fuse.h | 34 + include/uapi/linux/virtio_fs.h | 44 ++ include/uapi/linux/virtio_ids.h | 1 + include/uapi/linux/virtio_mmio.h | 11 + include/uapi/linux/virtio_pci.h | 10 + 26 files changed, 2875 insertions(+), 149 deletions(-) create mode 100644 fs/fuse/virtio_fs.c create mode 100644 include/uapi/linux/virtio_fs.h -- 2.20.1
