Hi, On Saturday, January 4, 2020 at 11:08:29 AM UTC-5, fo...@windowslive.com wrote: > > Hello, > > I am Fotis, currently an undergraduate ECE student in Athens, Greece. > > I 've been looking into Virtio-FS and adding support for it in OSv seems > pretty interesting. I have read the documentation in the wiki as well as > the documentation directory in the repo and I was starting to read the code > for existing filesystems and virtio devices. I 'd like to ask though if > there is any other relevant documentation (or code) you think would be > helpful. > > Also, in addition to the requirements mentioned in the GitHub issue > <https://github.com/cloudius-systems/osv/issues/1062>, are you aware of > any other major blockers that could surface? How difficult and time > consuming do you think this could prove to be in general? > Virtio-FS is definitely in the "bleeding edge" category. It has only been merged into Linux codebase couple of month ago ( https://www.phoronix.com/scan.php?page=news_item&px=Linux-5.4-VirtIO-FS) and I do not think it has been merged into QEMU codebase yet. It is not even part of the last finalized virtio 1.1 spec, I think (will be part of 1.2?). Having said all that, I still think it would be a very big win even if OSv supported some minimal version of it. That is why I suggested starting with the read-only part of it which should make initialial implementation easier. Even that would be super helpful as OSv could read and execute the application code from the host instead of putting them inside of the image (I am not sure what exactly the security implications of it would be). I also think that Firecracker team is planning to add virtio-fs support ( https://github.com/firecracker-microvm/firecracker/issues/1180 and https://github.com/firecracker-microvm/firecracker/pull/1351).
As far as how to go about implementing read-only part of virtio-fs in OSv, I would break it down into two major pieces: - virtio driver for virtio-fs per what is in the spec (class inheriting from virtio-driver); look for the examples at virtio-blk.* and virtio-scsi.* under drivers, the class diagrams from this article may help as well - http://blog.osv.io/blog/2019/04/19/making-OSv-run-on-firecraker/ - new vfs layer for virtio-fs - would go under fs; look at rofs implementation https://github.com/cloudius-systems/osv/tree/master/fs/rofs for an example as it implements exactly the subset of VFS operations we would need for read-only version of virtio-fs (please ignore the cache layer logic in rofs as it would not apply to virtio-fs). Now the challenge is that "normal" file system implementations in OSv like ZFS or ROFS can work with any block device and driver like virtio-blk, virtio-scsi, ide, etc using the bio abstraction. For example, see this piece of code in ROFS - https://github.com/cloudius-systems/osv/blob/69a0ce39eb7c5af76bd2c714939c02ceb7ea398f/fs/rofs/rofs_common.cc#L60-L85 - where it simply specifies the offset at and number of bytes to read from the block device. In virtio-fs, as I am guessing (and might be wrong) it would be different as it operates at the vnode level (files and directories) instead of raw block device. So we have a bit of a "conflict of abstractions". This means that new drivers/virtio-fs driver class would NOT implement functions like blk_strategy(), blk_read(), blk_write() that use bio struct, instead it would implement some different interface - not sure what yet. Also, VFS layer for virtio-fs would be more similar to what we do for nfs (see https://github.com/cloudius-systems/osv/blob/master/fs/nfs/nfs_vnops.cc) where we also do not read/write from a block device - instead we read/write over the network using a socket. Obviously, in case of fs/virtiofs it would interact directly with virtio-fs driver, I think. I hope it is good information for starters. As you go along we will guide you more. All in all I do not think implementing the read-only part of virtio-fs would be a big or complicated effort. At least that is what it seems. Regards, Waldek > > Thank you! > > Τη Σάββατο, 27 Απριλίου 2019 - 6:55:06 π.μ. UTC+3, ο χρήστης Waldek > Kozaczuk έγραψε: >> >> It is supposed to be part of VirtIO at some point. I think NEMU (and >> possibly QEMU 4.0) might support it - >> https://github.com/intel/nemu/issues/211. >> >> It would be nice to investigate it a little. >> >> - https://lkml.org/lkml/2018/12/10/615 >> - https://gitlab.com/virtio-fs >> - >> https://lists.oasis-open.org/archives/virtio-dev/201812/msg00073.html >> >> Maybe better long term than 9P FS? >> >> Waldek >> >> >> -- You received this message because you are subscribed to the Google Groups "OSv Development" group. To unsubscribe from this group and stop receiving emails from it, send an email to osv-dev+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/osv-dev/05b8604f-d875-476f-baa0-476700539d65%40googlegroups.com.
