From: Dr. David Alan Gilbert <dgilb...@redhat.com> * Fotis Xenakis (fo...@windowslive.com) wrote: > This post briefly goes over the main points of virtio-fs and OSv, a > unikernel running under QEMU/KVM and taking advantage of its virtio-fs > implementation. > > Changes since v1: > - Fixed wording and links, as suggested by Thomas Huth. > - Added a short example of virtio-fs usage in OSv. > > Signed-off-by: Fotis Xenakis <fo...@windowslive.com>
> +One central point is OSv's support for booting from virtio-fs: this enables > +deploying a modified version or a whole new application **without > rebuilding** > +the image, just by adjusting its root file system contents on the host. Last, > +owing to the DAX window practically providing low-overhead access to the > host's > +page cache, scalability is also expected to excel, with it being a common > +concern due to the potentially high density of unikernels per host. Hi Fotis, Hello Dave, Since I'm not used to unikernels, I'm a little confused by this; I'd appreciate some explanation. In your unikernel, does the root filesystem just contain data? I mean being a 'unikernel' aren't all the binaries and support all linked into the kernel itself? Short answer: the root file system doesn't contain only data, the executable can also be loaded from it. Although a unikernel, it supports both the embedded-in-kernel and separate-filesystem approaches. OSv is more heavy-weight than most unikernels, in the sense that it supports a lot of features found in general-purpose OSs. One could just describe it as a specialized, light-weight OS. On the filesystem side, it's actually pretty close e.g. to Linux: it has a VFS and multiple filesystems: * pseudo-fs (devfs and others) * ramfs, which is indeed embedded into the kernel * ZFS and ROFS, on regular block devices * NFS, virtio-fs Also like Linux, it initially boots into its initramfs (embedded in the kernel) and then typically mounts a root file system from a device (ZFS, ROFS or virtio-fs), before executing the application code. In case this is not clear, please feel free to ask further! Fotis Dave -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK