add blog post about virtio 9p

README.md

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+# static
+
+My static website written in Jekyll.
+Deployment through Concourse.
+
 `fly -t home set-pipeline --load-vars-from=secrets.yml -p static -c pipeline.yml`

jekyll/README.md

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+`jekyll serve`

jekyll/_posts/virtio-9p-experiences/2023-05-31-virtio-9p-experiences.md

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+---
+layout: post
+title:  My Experiences with virtio-9p
+date:   2023-05-31 14:18:00 Europe/Amsterdam
+categories: libvirt virtio 9p
+---
+
+When I was scaling up my home lab, I started thinking more about data management.
+I hadn't (and still haven't) set up any form of network storage.
+I have, however, set up a backup mechanism using [Borg](https://borgbackup.readthedocs.io/en/stable/).
+Still, I want to operate lots of virtual machines, and backing up each one of them separately seemed excessive.
+So I started thinking, what if I just let the host machines back up the data?
+After all, the amount of physical hosts I have in my home lab is unlikely to increase drastically.
+
+# The Use Case for Sharing Directories
+
+I started working out this idea further.
+Without network storage, I needed a way for guest VMs to access the host's disks.
+Here there are two possibilities, either expose some block device or a file system.
+Creating a whole virtual disk for just the data of some VMs seemed wasteful, and from my experiences also increases backup times dramatically.
+I therefore searched for a way to mount a directory from the host OS on the guest VM.
+This is when I stumbled upon [this blog](https://rabexc.org/posts/p9-setup-in-libvirt) post talking about sharing directories with virtual machines.
+
+# Sharing Directories with virtio-9p
+
+virtio-9p is a way to map a directory on the host OS to a special device on the virtual machine.
+In `virt-manager`, it looks like the following:
+![picture showing virt-manager configuration to map a directory to a VM](virt-manager.png)
+Under the hood, virtio-9p uses the 9pnet protocol.
+Originally developed at Bell Labs, support for this is available in all modern Linux kernels.
+If you share a directory with a VM, you can then mount it.
+Below is an extract of my `/etc/fstab` to automatically mount the directory:
+```
+data	/mnt/data	9p	trans=virtio,rw	0	0
+```
+
+The first argument (`data`) refers to the name you gave this share from the host
+With the `trans` option we specify that this is a virtio share.
+
+# Problems with virtio-9p
+
+At first I had no problems with my setup, but I am now contemplating just moving to a network storage based setup because of two problems.
+
+The first problem is that some files have suddenly changed ownership from `libvirt-qemu` to `root`.
+If the file is owned by `root`, the guest OS can still see it, but cannot access it.
+I am not entirely sure the problem lies with virtio, but I suspect it is.
+For anyone experiencing this problem, I wrote a small shell script to revert ownership to the `libvirt-qemu` user:
+```shell
+find -printf "%h/%f %u\n"  | grep root | cut -d ' ' -f1 | xargs chown libvirt-qemu:libvirt-qemu
+```
+
+Another problem that I have experienced, is guests being unable to mount the directory at all.
+I have only experienced this problem once, but it was highly annoying.
+To fix it, I had to reboot the whole physical machine.
+
+# Alternatives
+
+virtio-9p seemed like a good idea, but as discussed, I had some problems with it.
+It seems [virtioFS](https://virtio-fs.gitlab.io/) might be a an interesting alternative as it is designed specifically for sharing directories with VMs.
+
+As for me, I will probably finally look into deploying network storage either with NFS or SSHFS.