Migrate VM shares from 9p to virtiofs; update QEMU and doctor

cmd/qvm/doctor.go

@@ -10,6 +10,7 @@ import (
 	"qvm/internal/workspace"
 	"strconv"
 	"strings"
+	"syscall"
 
 	"github.com/spf13/cobra"
 )
@@ -232,7 +233,7 @@ func checkVirtiofsdSockets() []string {
 			continue
 		}
 
-		if err := process.Signal(os.Signal(nil)); err != nil {
+		if err := process.Signal(syscall.Signal(0)); err != nil {
 			issues = append(issues, fmt.Sprintf("Orphaned virtiofsd socket: %s (process %d not running)", sock, pid))
 		}
 	}

flake/default-vm/flake.nix

@@ -130,71 +130,42 @@
           # Josh's timezone
           time.timeZone = "America/Chicago";
 
-          # Git safe.directory for 9p ownership issues
+          # Git safe.directory for virtiofs ownership issues
           environment.etc."gitconfig".text = ''
             [safe]
               directory = *
           '';
 
-          # 9p mount points for caches (must match qvm-start mount tags)
+          # virtiofs mount points for caches (must match qvm virtiofsd mount tags)
+          # Using virtiofs instead of 9p for better performance and hot-mount support
           fileSystems."/cache/cargo" = {
             device = "cargo_home";
-            fsType = "9p";
+            fsType = "virtiofs";
-            options = [
+            options = [ "nofail" ];
-              "trans=virtio"
-              "version=9p2000.L"
-              "msize=104857600"
-              "_netdev"
-              "nofail"
-            ];
           };
 
           fileSystems."/cache/target" = {
             device = "cargo_target";
-            fsType = "9p";
+            fsType = "virtiofs";
-            options = [
+            options = [ "nofail" ];
-              "trans=virtio"
-              "version=9p2000.L"
-              "msize=104857600"
-              "_netdev"
-              "nofail"
-            ];
           };
 
           fileSystems."/cache/pnpm" = {
             device = "pnpm_store";
-            fsType = "9p";
+            fsType = "virtiofs";
-            options = [
+            options = [ "nofail" ];
-              "trans=virtio"
-              "version=9p2000.L"
-              "msize=104857600"
-              "_netdev"
-              "nofail"
-            ];
           };
 
           fileSystems."/cache/sccache" = {
             device = "sccache";
-            fsType = "9p";
+            fsType = "virtiofs";
-            options = [
+            options = [ "nofail" ];
-              "trans=virtio"
-              "version=9p2000.L"
-              "msize=104857600"
-              "_netdev"
-              "nofail"
-            ];
           };
 
           fileSystems."/root/.config/opencode" = {
             device = "opencode_config";
-            fsType = "9p";
+            fsType = "virtiofs";
-            options = [
+            options = [ "nofail" ];
-              "trans=virtio"
-              "version=9p2000.L"
-              "msize=104857600"
-              "_netdev"
-              "nofail"
-            ];
           };
 
           # Environment variables for cache directories
@@ -215,47 +186,46 @@
             "d /cache/sccache 0755 root root -"
           ];
 
-          # Systemd mount units for cache directories
+          # Systemd mount units for cache directories using virtiofs
-          # The NixOS VM runner doesn't include custom fileSystems entries in the generated fstab,
+          # virtiofs provides better performance than 9p and supports hot-mounting
-          # so we use systemd mount units to automount the 9p virtfs shares at boot.
           systemd.mounts = [
             {
               what = "cargo_home";
               where = "/cache/cargo";
-              type = "9p";
+              type = "virtiofs";
-              options = "trans=virtio,version=9p2000.L,msize=104857600,nofail";
+              options = "nofail";
               wantedBy = [ "multi-user.target" ];
               after = [ "systemd-modules-load.service" ];
             }
             {
               what = "cargo_target";
               where = "/cache/target";
-              type = "9p";
+              type = "virtiofs";
-              options = "trans=virtio,version=9p2000.L,msize=104857600,nofail";
+              options = "nofail";
               wantedBy = [ "multi-user.target" ];
               after = [ "systemd-modules-load.service" ];
             }
             {
               what = "pnpm_store";
               where = "/cache/pnpm";
-              type = "9p";
+              type = "virtiofs";
-              options = "trans=virtio,version=9p2000.L,msize=104857600,nofail";
+              options = "nofail";
               wantedBy = [ "multi-user.target" ];
               after = [ "systemd-modules-load.service" ];
             }
             {
               what = "sccache";
               where = "/cache/sccache";
-              type = "9p";
+              type = "virtiofs";
-              options = "trans=virtio,version=9p2000.L,msize=104857600,nofail";
+              options = "nofail";
               wantedBy = [ "multi-user.target" ];
               after = [ "systemd-modules-load.service" ];
             }
             {
               what = "opencode_config";
               where = "/root/.config/opencode";
-              type = "9p";
+              type = "virtiofs";
-              options = "trans=virtio,version=9p2000.L,msize=104857600,nofail";
+              options = "nofail";
               wantedBy = [ "multi-user.target" ];
               after = [ "systemd-modules-load.service" ];
             }
@@ -298,15 +268,9 @@
           # GB disk size
           virtualisation.diskSize = 40 * 1024;
 
-          # NOTE: Using 9p virtfs for filesystem sharing
+          # NOTE: Using virtiofs for filesystem sharing (via virtiofsd + vhost-user-fs-pci)
-          # The NixOS VM runner doesn't support virtio-fs out of the box.
+          # This provides better performance than 9p and supports hot-mounting workspaces
-          # We use 9p (-virtfs) which is the standard method for QEMU VMs.
+          # without VM restart. The qvm CLI manages virtiofsd daemons for each mount.
-          # 
-          # See: https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/virtualisation/qemu-vm.nix#L530
-          # The sharedDirectories option hardcodes: -virtfs local,path=...,security_model=...
-          #
-          # 9p mounts are configured via QEMU_OPTS environment variable:
-          #   -virtfs local,path=$HOST_PATH,mount_tag=$TAG,security_model=mapped-xattr,msize=104857600
 
           system.stateVersion = stateVersion;
         };

internal/vm/qemu.go

@@ -12,13 +12,14 @@ import (
 func buildQEMUCommand(cfg *config.Config, sshPort int, mounts []virtiofsd.Mount) []string {
 	memSize := cfg.VM.Memory
 
-	// vhost-user-fs requires shared memory backend
+	// vhost-user-fs requires shared memory backend with share=on
+	// We must specify memory size only via the memory backend and attach it to NUMA
+	// The -m flag must match the memory backend size for QEMU to be happy
 	args := []string{
-		"-machine", "q35",
+		"-machine", "q35,memory-backend=mem",
 		"-accel", "kvm",
 		"-cpu", "host",
 		"-object", fmt.Sprintf("memory-backend-memfd,id=mem,size=%s,share=on", memSize),
-		"-numa", "node,memdev=mem",
 		"-smp", strconv.Itoa(cfg.VM.CPUs),
 		"-display", "none",
 		"-daemonize",