Use virtiofsd for sharing file system data with host

TODO: Unfinished. We solely rely on guest level read-only mounts to enforce read-only state. The recommended way is to use read-only bind mounts [0], but doing so would require root. Not using DAX, because it still is still incomplete and apparently requires building from source. Interestingly, there may be the option of just consuming the virtiofsd crate as a library and not require any shelling out. That would be *much* nicer, but the current APIs make this somewhat cumbersome. I'd think we'd pretty much have to reimplement their entire main() functionality [1]. I consider this way out of scope for this first version. I have adjusted the configs and tested fedora and arch. No idea what empty is about, really. [0] https://gitlab.com/virtio-fs/virtiofsd/-/blob/main/README.md?ref_type=heads#faq [1] https://gitlab.com/virtio-fs/virtiofsd/-/blob/main/src/main.rs?ref_type=heads#L1242 Resources: https://virtio-fs.gitlab.io/howto-boot.html khttps://virtio-fs.gitlab.io/howto-qemu.html khttps://wiki.hexchain.org/linux/generic/network-root/ khttps://gitlab.com/virtio-fs/virtiofsd/-/blob/main/README.md?ref_type=heads#examples
d-e-s-o · Aug 27, 2024 · 87c8792 · 87c8792
1 parent b713eba
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diff --git a/.github/workflows/rust.yml b/.github/workflows/rust.yml
@@ -16,7 +16,8 @@ env:
 jobs:
   build-test:
 
-    runs-on: ubuntu-latest
+    # ubuntu-24.04 is the earliest image with a `virtiofsd` package.
+    runs-on: ubuntu-24.04
 
     steps:
     - uses: actions/checkout@v3
@@ -36,7 +37,7 @@ jobs:
       run: |
         sudo apt-get update
         # Virtualization deps
-        sudo apt-get install -y qemu-system-x86-64 qemu-guest-agent qemu-utils ovmf
+        sudo apt-get install -y qemu-system-x86-64 qemu-guest-agent qemu-utils ovmf virtiofsd
 
     - name: Cache test assets
       uses: actions/cache@v3

diff --git a/README.md b/README.md
@@ -26,14 +26,15 @@ The following are required dependencies, grouped by location:
 
 Host machine:
 
-* [`qemu`](https://pkgs.org/download/qemu)
+* [`qemu`](https://pkgs.org/download/qemu) (version 5.9 or higher)
 * [`qemu-guest-agent`](https://pkgs.org/search/?q=qemu-guest-agent)
 * [`OVMF`](https://pkgs.org/download/ovmf)
+* [`virtiofsd`](https://gitlab.com/virtio-fs/virtiofsd)
 
 Virtual machine image:
 
 * `qemu-guest-agent`
-* Kernel 9p filesystem support, either compiled in or as modules (see kernel
+* Kernel `virtiofs` support, either compiled in or as modules (see kernel
   dependencies)
     * Most (if not all) distros already ship support as modules or better
 
@@ -42,9 +43,8 @@ Kernel:
 * `CONFIG_VIRTIO=y`
 * `CONFIG_VIRTIO_PCI=y`
 * `CONFIG_VIRTIO_CONSOLE=y`
-* `CONFIG_NET_9P=y`
-* `CONFIG_NET_9P_VIRTIO=y`
-* `CONFIG_9P_FS=y`
+* `CONFIG_FUSE_FS=y`
+* `CONFIG_VIRTIO_FS=y`
 
 Note the virtual machine image dependencies are only required if you're using
 the `image` target parameter. Likewise, the same applies for kernel

diff --git a/src/lib.rs b/src/lib.rs
@@ -17,3 +17,4 @@ pub use crate::vmtest::*;
 mod qemu;
 mod qga;
 mod util;
+mod virtiofsd;
diff --git a/src/output.rs b/src/output.rs
@@ -10,6 +10,11 @@ use anyhow::Result;
 /// Receivers should treat failures as terminal and not expect any more
 /// updates.
 pub enum Output {
+    /// On-host initialization starts
+    InitializeStart,
+    /// Initialization finished with provided with provided result
+    InitializeEnd(Result<()>),
+
     /// VM boot begins
     BootStart,
     /// Output related to VM boot

diff --git a/src/qemu.rs b/src/qemu.rs
@@ -27,18 +27,17 @@ use tinytemplate::{format_unescaped, TinyTemplate};
 use crate::output::Output;
 use crate::qga::QgaWrapper;
 use crate::util::gen_sock;
+use crate::virtiofsd::Virtiofsd;
 use crate::{Mount, Target, VMConfig};
 
 const INIT_TEMPLATE: &str = include_str!("init/init.sh.template");
 const COMMAND_TEMPLATE: &str = include_str!("init/command.template");
-// Needs to be `/dev/root` for kernel to "find" the 9pfs as rootfs
-const ROOTFS_9P_FS_MOUNT_TAG: &str = "/dev/root";
-const SHARED_9P_FS_MOUNT_TAG: &str = "vmtest-shared";
+const ROOT_FS_MOUNT_TAG: &str = "rootfs";
+const SHARED_FS_MOUNT_TAG: &str = "vmtest-shared";
 const COMMAND_OUTPUT_PORT_NAME: &str = "org.qemu.virtio_serial.0";
 const MAGIC_INTERACTIVE_COMMAND: &str = "-";
 
-const SHARED_9P_FS_MOUNT_PATH: &str = "/mnt/vmtest";
-const MOUNT_OPTS_9P_FS: &str = "trans=virtio,cache=mmap,msize=1048576";
+const SHARED_FS_MOUNT_PATH: &str = "/mnt/vmtest";
 const OVMF_PATHS: &[&str] = &[
     // Fedora
     "/usr/share/edk2/ovmf/OVMF_CODE.fd",
@@ -55,6 +54,8 @@ type QmpUnixStream = qapi::Stream<BufReader<UnixStream>, UnixStream>;
 /// Represents a single QEMU instance
 pub struct Qemu {
     process: Command,
+    /// `virtiofsd` instances for each of the mounts in use.
+    virtiofsds: Vec<Virtiofsd>,
     qga_sock: PathBuf,
     qmp_sock: PathBuf,
     command: String,
@@ -241,6 +242,18 @@ fn guest_agent_args(sock: &Path) -> Vec<OsString> {
     args
 }
 
+/// Generate general arguments necessary for working with `virtiofs`.
+fn virtiofs_general_args(vm: &VMConfig) -> Vec<OsString> {
+    let mut args: Vec<OsString> = Vec::new();
+
+    args.push("-object".into());
+    args.push(format!("memory-backend-memfd,id=mem,share=on,size={}", vm.memory.as_str()).into());
+    args.push("-numa".into());
+    args.push("node,memdev=mem".into());
+
+    args
+}
+
 /// Generate arguments for full KVM virtualization if host supports it
 fn kvm_args(arch: &str) -> Vec<&'static str> {
     let mut args = Vec::new();
@@ -291,30 +304,17 @@ fn machine_protocol_args(sock: &Path) -> Vec<OsString> {
     args
 }
 
-/// Generate arguments for setting up 9p FS server on host
+/// Generate per-file-system arguments necessary for working with `virtiofs`.
 ///
-/// `id` is the ID for the FS export (currently unused AFAICT)
+/// `id` is the ID for the FS export
 /// `mount_tag` is used inside guest to find the export
-fn plan9_fs_args(host_shared: &Path, id: &str, mount_tag: &str, ro: bool) -> Vec<OsString> {
+fn virtiofs_per_fs_args(virtiofsd: &Virtiofsd, id: &str, mount_tag: &str) -> Vec<OsString> {
     let mut args: Vec<OsString> = Vec::new();
 
-    args.push("-virtfs".into());
-
-    let mut arg = OsString::new();
-    arg.push(format!("local,id={id},path="));
-    arg.push(if host_shared.as_os_str().is_empty() {
-        // This case occurs when the config file path is just "vmtest.toml"
-        Path::new(".")
-    } else {
-        host_shared
-    });
-    arg.push(format!(
-        ",mount_tag={mount_tag},security_model=none,multidevs=remap"
-    ));
-    if ro {
-        arg.push(",readonly=on")
-    }
-    args.push(arg);
+    args.push("-chardev".into());
+    args.push(format!("socket,id={id},path={}", virtiofsd.socket_path().display()).into());
+    args.push("-device".into());
+    args.push(format!("vhost-user-fs-pci,queue-size=1024,chardev={id},tag={mount_tag}").into());
 
     args
 }
@@ -371,9 +371,9 @@ fn kernel_args(
     // The guest kernel command line args
     let mut cmdline: Vec<OsString> = Vec::new();
 
-    // Tell kernel the rootfs is 9p
-    cmdline.push("rootfstype=9p".into());
-    cmdline.push(format!("rootflags={}", MOUNT_OPTS_9P_FS).into());
+    // Tell kernel the rootfs is on a virtiofs and what "tag" it uses.
+    cmdline.push("rootfstype=virtiofs".into());
+    cmdline.push(format!("root={ROOT_FS_MOUNT_TAG}").into());
 
     // Mount rootfs readable/writable to make experience more smooth.
     // Lots of tools expect to be able to write logs or change global
@@ -455,16 +455,6 @@ fn vmconfig_args(vm: &VMConfig) -> Vec<OsString> {
         vm.memory.clone().into(),
     ];
 
-    for mount in vm.mounts.values() {
-        let name = format!("mount{}", hash(&mount.host_path));
-        args.append(&mut plan9_fs_args(
-            &mount.host_path,
-            &name,
-            &name,
-            !mount.writable,
-        ));
-    }
-
     let mut extra_args = vm
         .extra_args
         .clone()
@@ -650,6 +640,7 @@ impl Qemu {
         let command_sock = gen_sock("cmdout");
         let (init, guest_init) = gen_init(&target.rootfs).context("Failed to generate init")?;
 
+        let mut virtiofsds = Vec::new();
         let mut c = Command::new(format!("qemu-system-{}", target.arch));
 
         c.args(QEMU_DEFAULT_ARGS)
@@ -660,6 +651,7 @@ impl Qemu {
             .args(machine_args(&target.arch))
             .args(machine_protocol_args(&qmp_sock))
             .args(guest_agent_args(&qga_sock))
+            .args(virtiofs_general_args(&target.vm))
             .args(virtio_serial_args(&command_sock));
         // Always ensure the rootfs is first.
         if let Some(image) = &target.image {
@@ -668,28 +660,42 @@ impl Qemu {
                 c.args(uefi_firmware_args(target.vm.bios.as_deref()));
             }
         } else if let Some(kernel) = &target.kernel {
-            c.args(plan9_fs_args(
-                target.rootfs.as_path(),
+            let virtiofsd = Virtiofsd::new(target.rootfs.as_path())?;
+            c.args(virtiofs_per_fs_args(
+                    &virtiofsd,
                 "root",
-                ROOTFS_9P_FS_MOUNT_TAG,
-                false,
+                ROOT_FS_MOUNT_TAG,
             ));
             c.args(kernel_args(
                 kernel,
                 &target.arch,
                 guest_init.as_path(),
                 target.kernel_args.as_ref(),
             ));
+            virtiofsds.push(virtiofsd);
         } else {
             panic!("Config validation should've enforced XOR");
         }
+
         // Now add the shared mount and other extra mounts.
-        c.args(plan9_fs_args(
-            host_shared,
+        let virtiofsd = Virtiofsd::new(host_shared)?;
+        c.args(virtiofs_per_fs_args(
+            &virtiofsd,
             "shared",
-            SHARED_9P_FS_MOUNT_TAG,
-            false,
+            SHARED_FS_MOUNT_TAG,
         ));
+        virtiofsds.push(virtiofsd);
+
+        for mount in target.vm.mounts.values() {
+            let name = format!("mount{}", hash(&mount.host_path));
+            let virtiofsd = Virtiofsd::new(&mount.host_path)?;
+            c.args(virtiofs_per_fs_args(
+                &virtiofsd,
+                &name,
+                &name,
+            ));
+            virtiofsds.push(virtiofsd);
+        }
         c.args(vmconfig_args(&target.vm));
 
         if log_enabled!(Level::Error) {
@@ -706,6 +712,7 @@ impl Qemu {
 
         let mut qemu = Self {
             process: c,
+            virtiofsds,
             qga_sock,
             qmp_sock,
             command: target.command.to_string(),
@@ -838,16 +845,18 @@ impl Qemu {
         // We can race with VM/qemu coming up. So retry a few times with growing backoff.
         let mut rc = 0;
         for i in 0..5 {
-            let mount_opts = if ro {
-                format!("{},ro", MOUNT_OPTS_9P_FS)
-            } else {
-                MOUNT_OPTS_9P_FS.into()
-            };
+            let mut args = vec![
+                "-t", "virtiofs", mount_tag, guest_path
+            ];
+            if ro {
+                args.push("-oro")
+            }
+
             rc = run_in_vm(
                 qga,
                 &output_fn,
                 "mount",
-                &["-t", "9p", "-o", &mount_opts, mount_tag, guest_path],
+                &args,
                 false,
                 None,
             )?;
@@ -1052,7 +1061,7 @@ impl Qemu {
         // Mount shared directory inside guest
         let _ = self.updates.send(Output::SetupStart);
         if let Err(e) =
-            self.mount_in_guest(qga, SHARED_9P_FS_MOUNT_PATH, SHARED_9P_FS_MOUNT_TAG, false)
+            self.mount_in_guest(qga, SHARED_FS_MOUNT_PATH, SHARED_FS_MOUNT_TAG, false)
         {
             return Err(e).context("Failed to mount shared directory in guest");
         }
@@ -1075,6 +1084,21 @@ impl Qemu {
     /// Errors and return status are reported through the `updates` channel passed into the
     /// constructor.
     pub fn run(mut self) {
+        let _ = self.updates.send(Output::InitializeStart);
+        for phase_fn in [Virtiofsd::launch, Virtiofsd::await_launched] {
+            for virtiofsd in self.virtiofsds.iter_mut() {
+                match phase_fn(virtiofsd) {
+                    Ok(()) => (),
+                    Err(e) => {
+                        let _ = self.updates.send(Output::InitializeEnd(Err(e)));
+                        return;
+                    }
+                }
+            }
+        }
+
+        let _ = self.updates.send(Output::InitializeEnd(Ok(())));
+
         // Start QEMU
         let (mut child, qga, mut qmp) = match self.boot_vm() {
             Ok((c, qga, qmp)) => (c, qga, qmp),

diff --git a/src/ui.rs b/src/ui.rs
@@ -177,6 +177,16 @@ impl Ui {
             };
 
             match &msg {
+                Output::InitializeStart => {
+                    stage = Stage::new(term.clone(), &heading("Initializing host environment", 2), Some(stage));
+                    stages += 1;
+                }
+                Output::InitializeEnd(r) => {
+                    if let Err(e) = r {
+                        error_out_stage(&mut stage, e);
+                        errors += 1;
+                    }
+                }
                 Output::BootStart => {
                     stage = Stage::new(term.clone(), &heading("Booting", 2), Some(stage));
                     stages += 1;