nixvm: automatically mount when --vm-dir is used

changed the share arg from viofs to virtiofs as it is closer to the
actual name.

Signed-off-by: Joel Granados <[email protected]>

Author: Joelgranados

README.md

@@ -129,6 +129,37 @@ add the following text to your configruation file (usually /etc/nix/nix.conf):
     experimental-features = nix-command flakes
 
 
+### Mounting directories
+
+This is useful when selftests or modules are needed within the VM.
+
+1. Early mount: Add a `qemu_share_add` to your vmctl config
+
+    ```sh
+      qemu_share_add \
+        --shared-dir "/path/to/modules/lib/modules" \
+        --tag "modules" \
+        --share-type "virtiofs" \
+        --vm-dir "/lib/modules"
+    ```
+
+    If you want to share but not mount, remove the --vm-dir arg.
+
+2. Systemd mount: Add a "service" to your nix configuration:
+
+    ```nix
+        systemd.services.mount-user-virtiofs = {
+          description = "Mount virtiofsd tag 'selftests' to /usr/lib/kselftests";
+          after = [ "local-fs.target" ];
+          wantedBy = [ "multi-user.target" ];
+          serviceConfig = {
+            Type = "oneshot";
+            ExecStart = "/run/current-system/sw/bin/mount -t virtiofs user /usr/lib/kselftests";
+            RemainAfterExit = true;
+          };
+        };
+    ```
+
 ## Prep boot img
 
 The base configruation `*-base.conf` will look for a base image in

lib/qemu/nix

@@ -103,6 +103,11 @@ qemu_nix_add_noimgnix () {
 
   _qemu_nix_create_nix_init "${VMSTATE}"
 
+  qemu_share_add --shared-dir "${NIX_STORE_PATH}" \
+      --tag "nixstore" \
+      --share-type "virtiofs" \
+      --vm-dir "/nix/store"
+
   local nix_init_path=""
   nix_init_path="$(readlink "${dst_path}")/init"
   local cmd_line="root=/dev/ram0 console=${GUEST_KERNEL_CONSOLE}"
@@ -111,13 +116,14 @@ qemu_nix_add_noimgnix () {
   fi
   cmd_line="${cmd_line} ${cmd_line_extra}"
   cmd_line="${cmd_line} -- --init-path ${nix_init_path}"
-  cmd_line="${cmd_line} --mount nixstore,/nix/store,virtiofs"
+  if [[ -v NIX_MOUNTS ]]; then
+    for nmount in "${NIX_MOUNTS[@]}"; do
+      cmd_line="${cmd_line} --mount ${nmount}"
+    done
+  fi
 
   QEMU_PARAMS+=("-kernel" "${kernel_dir}/${GUEST_KERNEL_IMAGE}")
   QEMU_PARAMS+=("-append" "${cmd_line}")
   QEMU_PARAMS+=("-initrd" "${VMSTATE}/init.img")
 
-  qemu_share_add --shared-dir "${NIX_STORE_PATH}" \
-      --tag "nixstore" \
-      --share-type "viofs"
 }

lib/qemu/share

@@ -43,7 +43,7 @@ qemu_share_add_9p() {
 }
 
 qemu_share_add() {
-  local long="shared-dir:,tag:,share-type:"
+  local long="shared-dir:,tag:,share-type:,vm-dir:"
 
   if ! tmp=$(getopt -o "" --long "$long" -n "${FUNCNAME[0]}" -- "$@"); then
     exit 1
@@ -63,6 +63,9 @@ qemu_share_add() {
       '--tag' )
         local tag="$2"; shift 2;
         ;;
+      '--vm-dir' )
+        local vm_dir="$2"; shift 2;
+        ;;
       '--' )
         shift; break
         ;;
@@ -90,10 +93,17 @@ qemu_share_add() {
 
   if [[ "${share_type}" == "9p" ]]; then
     qemu_share_add_9p "${shared_dir}" "${tag}"
-  elif [[ "${share_type}" == "viofs" ]]; then
+  elif [[ "${share_type}" == "virtiofs" ]]; then
     qemu_share_add_virtiofsd "${shared_dir}" "${tag}"
   else
     _fatal 1 "${FUNCNAME[0]}: Unknown directory share type (${share_type})"
   fi
+
+  if [[ -v vm_dir ]]; then
+    if [[ ! -v NIX_STORE_PATH ]]; then
+      _log "vm-dir ignored! it's only active in NIX"
+    fi
+    NIX_MOUNTS+=("${tag},${vm_dir},${share_type}")
+  fi
 }