WangLu's Notes

My daily driver setup has been working exceptionally well. If you missed them, you can check out the previous posts for details: Part 1 Part 2 Part 3 Recently, I decided to harden my setup by writing custom AppArmor profiles and nftables rules. During my research, libvirt kept popping up in tutorials. In fact, most “QEMU/KVM” guides simply assume you are using it. Initially, I decided against using libvirt because I wasn’t a fan of its design philosophy. However, I kept hearing that it can automatically generate AppArmor profiles and firewall rules for each VM. Furthermore, this article highlighted several things that libvirt genuinely simplifies. Intrigued, I decided to dive in and get some first-hand experience. The plan was to migrate my existing VM setup (which relies on bare QEMU scripts) to libvirt to see if it was a good fit. I specifically wanted to evaluate the parts of libvirt I was previously skeptical about: Reliance on a highly privileged daemon. Configuration stored...

I have a USB game controller that works flawlessly during gameplay, but it keeps disconnecting and reconnecting every ~40 seconds whenever it is left idle. While it is mostly harmless in practice, it is annoying to see the kernel messages are flooded with messages about the game controller. Many online resources, such as the Arch Wiki , suggest disabling USB autosuspend to fix this. Unfortunately, that didn’t solve the issue in my case. I suspect the controller expects to be continuously polled rather than entering a power-saving state, especially since it immediately tries to reconnect after dropping. Since I primarily use this controller by passing it through to a VM, I needed a way to manually manage its connection state. Here is the workaround that eventually did the trick: Add the following rule to udev . This ensures the controller is ignored by the host system upon connection. ACTION=="add", SUBSYSTEM=="usb", ATTR{idVendor}=="xxxx", ATTR{idProdu...

Now that I have my VMs running, what if I want to switch between them? What if I want to put the VM or the host to sleep, or shut them down? In this post, I’ll discuss a few options. Just a quick overview of my setup: Only one VM is running at a time. All VMs have GPU passthrough, and the GPU is connected to a display. I have a secondary display, which I prefer not to use unless absolutely necessary. See also: Part 1 Part 2 Option 1: Deep Integration with Guest OS Ideally, I could just click on a “Power off and Switch to VM X” menu from within the guest OS. This isn’t difficult to support on the host side: the guest OS could pass the VM name to the host (e.g., via a serial port), and the host would automatically start the next VM when the current one exits. However, I didn’t find an easy way to implement this menu, especially considering I plan to support multiple operating systems. I also couldn’t find a way to prevent the guest from shutting down without providing the next V...

Previously, I decided to set up a headless VM orchestrator for daily driving and gaming. In general, installing a minimal Debian and QEMU is fairly straightforward, but the devil is in the details. Here are my notes on the process. See also: part 1 Overall Setup The machine is a laptop. The built-in display is connected to the iGPU, and an external display is connected to the dGPU. I prefer to use only the external display; the built-in one is rarely used. I have two VMs: one as a daily driver and the other for gaming. Both have GPU passthrough. Only one runs at a time. Resources Reserved for the Host CPU: 1 core, 2 threads. RAM: 2GB (typical usage is around 500MB). Disk: 32GB. The OS only needs ~2GB, but I need extra space for cache, log, OS images, etc. CPU The main QEMU process and IO thread should be pinned to the host CPUs. vCPU threads should be pinned to the CPUs reserved for the VM. CPU pinning cannot be done through QEMU command-line arguments. I had to talk to the QEM...

For years, I've been playing games and doing everything else on the same PC. Hoever, after a recent positive experience with Qubes OS, I no longer feel comfortable keeping my games, passwords, and other stuff all in the same place. Because of this, I decided to change my gaming setup. My requirements are: Performance. Gaming should be functional and playable. Isolation. At a minimum, game binaries should not have access to my other files. Quick Switch. I need to be able to switch between gaming and non-gaming easily. Single Display. All my workflows should be performance well on a single display. I do have a secondary display, but I want to rarely use it. So, here goes my adeventure. Option 1: Dual Boot This is the classic solution, which sounds boring but almost always works. Performance: Good. All operating systems have direct access to physical hardware. Isolation: OK-ish, each OS technically has access to all data from other OSes. Disk encryption and Secure Boot can mitigate th...

After a routine system update and an unfortunate hang that required a hard reset, my Linux machine refused to boot. Instead of the familiar login prompt, I was greeted by a cryptic GRUB error:  error: no cryptodisk module can handle this device. My setup uses LUKS2 + LVM. From the GRUB rescue shell, I could actually decrypt the LUKS container. But once decrypted, GRUB completely failed to detect any LVM volumes. It simply acted as if the LVM structure didn't exist. Meanwhile, if I boot it from a Live Rescue USB, everything worked perfectly. I could open the LUKS container, and the volume group appeared immediately. Tools like  vgck  and  pvck  reported no issues. After a length discussion with AI, eventually I found the magical commands: vgcfgbackup -f lvm_backup.txt <vg_name> vgcfgrestore -f lvm_backup.txt <vg_name> After running these commands and rebooting, GRUB recognized the LVM volumes immediately, and I was back in my system. Supposedly this f...

I recently tried to install Qubes OS alongside an existing Windows installation. It turned out to be surprisingly difficult—way harder than my last attempt—likely due to a combination of my encrypted  /boot  setup and older hardware. Here are some notes from the process. Shrinking an NTFS Volume I needed to free up some space from a Windows NTFS volume. Normally, this just takes a few clicks in Disk Management. This time, however, Windows reported a "shrinkable volume" that was suspiciously small. Following  this answer , I tried the standard fixes: Disabled hibernation ( powercfg /h off ) Disabled the pagefile Disabled system protection This increased the shrinkable volume a bit, but nowhere near the actual free space left on the partition. Digging into the Windows Application logs in Event Viewer, I finally found the culprit:  The last unmovable file appears to be: \$Mft::$DATA . It turns out  $Mft  is a special block in NTFS that cannot be easily moved, ...

I've been running Qubes OS on Machine A alongside Windows for a while. My setup involved storing the unencrypted  /boot  partition and the LUKS header on an external USB drive. Recently, I planned to install Qubes on Machine B, also in a dual-boot configuration. However, the complexity jumped significantly: Machine B has Secure Boot enabled because BitLocker requires it. On previous installs, I grew tired of toggling Secure Boot in the BIOS every time I switched operating systems. I only have one USB drive. Managing separate  /boot  partitions for two different Qubes installations on a single thumb drive is messy. After some experimentation, I found a way to solve both problems. Sharing One USB Drive for Multiple Qubes Installations The solution is elegant: Don't store  /boot  on the USB drive. Instead, move  /boot  to the encrypted internal disk partition. The USB drive's only job is to unlock that partition and hand over control to the system. O...

After writing a Nonogram solver, I decided to tackle a Sudoku solver to practice Rust. My goal wasn't just to support classic Sudoku rules, but also to handle variants like Thermometer, Arrow, and Cage etc. 1. Brute Force It is fairly easy to write a brute force or backtracking algorithm. This approach is sufficient for most classic Sudoku puzzles, but it becomes unbearably slow as soon as variant rules are introduced. I considered this step a warmup—a baseline to improve upon. 2. Constraint Propagation Here, I tried to introduce "logical thinking" to the algorithm. I used  u16  as a bitmask to represent the possible values of a cell. Whenever a cell's state changes (due to guessing, backtracking, or propagation), the algorithm consults all constraints to eliminate impossible candidates. While Nonogram is technically an NP-Complete problem, in practice, my constraint-propagation solver (without guessing) can solve almost all puzzles found online. I’ve only seen one ex...