chore(tvix): move store/fs to castore/fs r/7256

With the recent introduction of the RootNodes trait, there's nothing in
the fs module pulling in tvix-store dependencies, so it can live in
tvix-castore.

This allows other crates to make use of TvixStoreFS, without having to
pull in tvix-store.

For example, a tvix-build using a fuse mountpoint at /nix/store doesn't
need a PathInfoService to hold the root nodes that should be present,
but just a list.

tvix-store now has a pathinfoservice/fs module, which contains the
necessary glue logic to implement the RootNodes trait for a
PathInfoService.

To satisfy Rust orphan rules for trait implementations, we had to add a
small wrapper struct. It's mostly hidden away by the make_fs helper
function returning a TvixStoreFs.

It can't be entirely private, as its still leaking into the concrete
type of TvixStoreFS.

tvix-store still has `fuse` and `virtiofs` features, but they now simply
enable these features in the `tvix-castore` crate they depend on.

The tests for the fuse functionality stay in tvix-store for now, as
they populate the root nodes through a PathInfoService.

Once above mentioned "list of root nodes" implementation exists, we
might want to shuffle this around one more time.

Fixes b/341.

Change-Id: I989f664827a5a361b23b34368d242d10c157c756
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10378
Autosubmit: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>

12 files changed, 106 insertions, 1376 deletions

diff --git a/tvix/store/src/bin/tvix-store.rs b/tvix/store/src/bin/tvix-store.rs
index e4f2e0801b81..bf59366eb34e 100644
--- a/tvix/store/src/bin/tvix-store.rs
+++ b/tvix/store/src/bin/tvix-store.rs
@@ -29,14 +29,14 @@ use tvix_store::proto::GRPCPathInfoServiceWrapper;
 use tvix_store::proto::NarInfo;
 use tvix_store::proto::PathInfo;
 
-#[cfg(feature = "fs")]
-use tvix_store::fs::TvixStoreFs;
+#[cfg(any(feature = "fuse", feature = "virtiofs"))]
+use tvix_store::pathinfoservice::make_fs;
 
 #[cfg(feature = "fuse")]
-use tvix_store::fs::fuse::FuseDaemon;
+use tvix_castore::fs::fuse::FuseDaemon;
 
 #[cfg(feature = "virtiofs")]
-use tvix_store::fs::virtiofs::start_virtiofs_daemon;
+use tvix_castore::fs::virtiofs::start_virtiofs_daemon;
 
 #[cfg(feature = "tonic-reflection")]
 use tvix_castore::proto::FILE_DESCRIPTOR_SET as CASTORE_FILE_DESCRIPTOR_SET;
@@ -365,7 +365,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
             let path_info_service: Arc<dyn PathInfoService> = path_info_service.into();
 
             let mut fuse_daemon = tokio::task::spawn_blocking(move || {
-                let f = TvixStoreFs::new(
+                let fs = make_fs(
                     blob_service,
                     directory_service,
                     path_info_service,
@@ -373,7 +373,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
                 );
                 info!("mounting tvix-store on {:?}", &dest);
 
-                FuseDaemon::new(f, &dest, threads)
+                FuseDaemon::new(fs, &dest, threads)
             })
             .await??;
 
@@ -409,7 +409,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
             let path_info_service: Arc<dyn PathInfoService> = path_info_service.into();
 
             tokio::task::spawn_blocking(move || {
-                let fs = TvixStoreFs::new(
+                let fs = make_fs(
                     blob_service,
                     directory_service,
                     path_info_service,
diff --git a/tvix/store/src/fs/file_attr.rs b/tvix/store/src/fs/file_attr.rs
deleted file mode 100644
index ad41f036a253..000000000000
--- a/tvix/store/src/fs/file_attr.rs
+++ /dev/null
@@ -1,53 +0,0 @@
-#![allow(clippy::unnecessary_cast)] // libc::S_IFDIR is u32 on Linux and u16 on MacOS
-use super::inodes::{DirectoryInodeData, InodeData};
-use fuse_backend_rs::abi::fuse_abi::Attr;
-
-/// The [Attr] describing the root
-pub const ROOT_FILE_ATTR: Attr = Attr {
-    ino: fuse_backend_rs::api::filesystem::ROOT_ID,
-    size: 0,
-    blksize: 1024,
-    blocks: 0,
-    mode: libc::S_IFDIR as u32 | 0o555,
-    atime: 0,
-    mtime: 0,
-    ctime: 0,
-    atimensec: 0,
-    mtimensec: 0,
-    ctimensec: 0,
-    nlink: 0,
-    uid: 0,
-    gid: 0,
-    rdev: 0,
-    flags: 0,
-    #[cfg(target_os = "macos")]
-    crtime: 0,
-    #[cfg(target_os = "macos")]
-    crtimensec: 0,
-    #[cfg(target_os = "macos")]
-    padding: 0,
-};
-
-/// for given &Node and inode, construct an [Attr]
-pub fn gen_file_attr(inode_data: &InodeData, inode: u64) -> Attr {
-    Attr {
-        ino: inode,
-        // FUTUREWORK: play with this numbers, as it affects read sizes for client applications.
-        blocks: 1024,
-        size: match inode_data {
-            InodeData::Regular(_, size, _) => *size as u64,
-            InodeData::Symlink(target) => target.len() as u64,
-            InodeData::Directory(DirectoryInodeData::Sparse(_, size)) => *size as u64,
-            InodeData::Directory(DirectoryInodeData::Populated(_, ref children)) => {
-                children.len() as u64
-            }
-        },
-        mode: match inode_data {
-            InodeData::Regular(_, _, false) => libc::S_IFREG as u32 | 0o444, // no-executable files
-            InodeData::Regular(_, _, true) => libc::S_IFREG as u32 | 0o555,  // executable files
-            InodeData::Symlink(_) => libc::S_IFLNK as u32 | 0o444,
-            InodeData::Directory(_) => libc::S_IFDIR as u32 | 0o555,
-        },
-        ..Default::default()
-    }
-}
diff --git a/tvix/store/src/fs/fuse.rs b/tvix/store/src/fs/fuse.rs
deleted file mode 100644
index 98793bf47d58..000000000000
--- a/tvix/store/src/fs/fuse.rs
+++ /dev/null
@@ -1,113 +0,0 @@
-use std::{io, path::Path, sync::Arc, thread};
-
-use fuse_backend_rs::{api::filesystem::FileSystem, transport::FuseSession};
-use tracing::error;
-
-struct FuseServer<FS>
-where
-    FS: FileSystem + Sync + Send,
-{
-    server: Arc<fuse_backend_rs::api::server::Server<Arc<FS>>>,
-    channel: fuse_backend_rs::transport::FuseChannel,
-}
-
-#[cfg(target_os = "macos")]
-const BADFD: libc::c_int = libc::EBADF;
-#[cfg(target_os = "linux")]
-const BADFD: libc::c_int = libc::EBADFD;
-
-impl<FS> FuseServer<FS>
-where
-    FS: FileSystem + Sync + Send,
-{
-    fn start(&mut self) -> io::Result<()> {
-        while let Some((reader, writer)) = self
-            .channel
-            .get_request()
-            .map_err(|_| io::Error::from_raw_os_error(libc::EINVAL))?
-        {
-            if let Err(e) = self
-                .server
-                .handle_message(reader, writer.into(), None, None)
-            {
-                match e {
-                    // This indicates the session has been shut down.
-                    fuse_backend_rs::Error::EncodeMessage(e) if e.raw_os_error() == Some(BADFD) => {
-                        break;
-                    }
-                    error => {
-                        error!(?error, "failed to handle fuse request");
-                        continue;
-                    }
-                }
-            }
-        }
-        Ok(())
-    }
-}
-
-pub struct FuseDaemon {
-    session: FuseSession,
-    threads: Vec<thread::JoinHandle<()>>,
-}
-
-impl FuseDaemon {
-    pub fn new<FS, P>(fs: FS, mountpoint: P, threads: usize) -> Result<Self, io::Error>
-    where
-        FS: FileSystem + Sync + Send + 'static,
-        P: AsRef<Path>,
-    {
-        let server = Arc::new(fuse_backend_rs::api::server::Server::new(Arc::new(fs)));
-
-        let mut session = FuseSession::new(mountpoint.as_ref(), "tvix-store", "", true)
-            .map_err(|e| io::Error::new(io::ErrorKind::Other, e.to_string()))?;
-
-        #[cfg(target_os = "linux")]
-        session.set_allow_other(false);
-        session
-            .mount()
-            .map_err(|e| io::Error::new(io::ErrorKind::Other, e.to_string()))?;
-        let mut join_handles = Vec::with_capacity(threads);
-        for _ in 0..threads {
-            let mut server = FuseServer {
-                server: server.clone(),
-                channel: session
-                    .new_channel()
-                    .map_err(|e| io::Error::new(io::ErrorKind::Other, e.to_string()))?,
-            };
-            let join_handle = thread::Builder::new()
-                .name("fuse_server".to_string())
-                .spawn(move || {
-                    let _ = server.start();
-                })?;
-            join_handles.push(join_handle);
-        }
-
-        Ok(FuseDaemon {
-            session,
-            threads: join_handles,
-        })
-    }
-
-    pub fn unmount(&mut self) -> Result<(), io::Error> {
-        self.session
-            .umount()
-            .map_err(|e| io::Error::new(io::ErrorKind::Other, e.to_string()))?;
-
-        for thread in self.threads.drain(..) {
-            thread.join().map_err(|_| {
-                io::Error::new(io::ErrorKind::Other, "failed to join fuse server thread")
-            })?;
-        }
-
-        Ok(())
-    }
-}
-
-impl Drop for FuseDaemon {
-    fn drop(&mut self) {
-        if let Err(error) = self.unmount() {
-            error!(?error, "failed to unmont fuse filesystem")
-        }
-    }
-}
diff --git a/tvix/store/src/fs/inode_tracker.rs b/tvix/store/src/fs/inode_tracker.rs
deleted file mode 100644
index 3cabbbd247b5..000000000000
--- a/tvix/store/src/fs/inode_tracker.rs
+++ /dev/null
@@ -1,207 +0,0 @@
-use std::{collections::HashMap, sync::Arc};
-
-use super::inodes::{DirectoryInodeData, InodeData};
-use tvix_castore::B3Digest;
-
-/// InodeTracker keeps track of inodes, stores data being these inodes and deals
-/// with inode allocation.
-pub struct InodeTracker {
-    data: HashMap<u64, Arc<InodeData>>,
-
-    // lookup table for blobs by their B3Digest
-    blob_digest_to_inode: HashMap<B3Digest, u64>,
-
-    // lookup table for symlinks by their target
-    symlink_target_to_inode: HashMap<bytes::Bytes, u64>,
-
-    // lookup table for directories by their B3Digest.
-    // Note the corresponding directory may not be present in data yet.
-    directory_digest_to_inode: HashMap<B3Digest, u64>,
-
-    // the next inode to allocate
-    next_inode: u64,
-}
-
-impl Default for InodeTracker {
-    fn default() -> Self {
-        Self {
-            data: Default::default(),
-
-            blob_digest_to_inode: Default::default(),
-            symlink_target_to_inode: Default::default(),
-            directory_digest_to_inode: Default::default(),
-
-            next_inode: 2,
-        }
-    }
-}
-
-impl InodeTracker {
-    // Retrieves data for a given inode, if it exists.
-    pub fn get(&self, ino: u64) -> Option<Arc<InodeData>> {
-        self.data.get(&ino).cloned()
-    }
-
-    // Replaces data for a given inode.
-    // Panics if the inode doesn't already exist.
-    pub fn replace(&mut self, ino: u64, data: Arc<InodeData>) {
-        if self.data.insert(ino, data).is_none() {
-            panic!("replace called on unknown inode");
-        }
-    }
-
-    // Stores data and returns the inode for it.
-    // In case an inode has already been allocated for the same data, that inode
-    // is returned, otherwise a new one is allocated.
-    // In case data is a [InodeData::Directory], inodes for all items are looked
-    // up
-    pub fn put(&mut self, data: InodeData) -> u64 {
-        match data {
-            InodeData::Regular(ref digest, _, _) => {
-                match self.blob_digest_to_inode.get(digest) {
-                    Some(found_ino) => {
-                        // We already have it, return the inode.
-                        *found_ino
-                    }
-                    None => self.insert_and_increment(data),
-                }
-            }
-            InodeData::Symlink(ref target) => {
-                match self.symlink_target_to_inode.get(target) {
-                    Some(found_ino) => {
-                        // We already have it, return the inode.
-                        *found_ino
-                    }
-                    None => self.insert_and_increment(data),
-                }
-            }
-            InodeData::Directory(DirectoryInodeData::Sparse(ref digest, _size)) => {
-                // check the lookup table if the B3Digest is known.
-                match self.directory_digest_to_inode.get(digest) {
-                    Some(found_ino) => {
-                        // We already have it, return the inode.
-                        *found_ino
-                    }
-                    None => {
-                        // insert and return the inode
-                        self.insert_and_increment(data)
-                    }
-                }
-            }
-            // Inserting [DirectoryInodeData::Populated] doesn't normally happen,
-            // only via [replace].
-            InodeData::Directory(DirectoryInodeData::Populated(..)) => {
-                unreachable!("should never be called with DirectoryInodeData::Populated")
-            }
-        }
-    }
-
-    // Inserts the data and returns the inode it was stored at, while
-    // incrementing next_inode.
-    fn insert_and_increment(&mut self, data: InodeData) -> u64 {
-        let ino = self.next_inode;
-        // insert into lookup tables
-        match data {
-            InodeData::Regular(ref digest, _, _) => {
-                self.blob_digest_to_inode.insert(digest.clone(), ino);
-            }
-            InodeData::Symlink(ref target) => {
-                self.symlink_target_to_inode.insert(target.clone(), ino);
-            }
-            InodeData::Directory(DirectoryInodeData::Sparse(ref digest, _size)) => {
-                self.directory_digest_to_inode.insert(digest.clone(), ino);
-            }
-            // This is currently not used outside test fixtures.
-            // Usually a [DirectoryInodeData::Sparse] is inserted and later
-            // "upgraded" with more data.
-            // However, as a future optimization, a lookup for a PathInfo could trigger a
-            // [DirectoryService::get_recursive()] request that "forks into
-            // background" and prepopulates all Directories in a closure.
-            InodeData::Directory(DirectoryInodeData::Populated(ref digest, _)) => {
-                self.directory_digest_to_inode.insert(digest.clone(), ino);
-            }
-        }
-        // Insert data
-        self.data.insert(ino, Arc::new(data));
-
-        // increment inode counter and return old inode.
-        self.next_inode += 1;
-        ino
-    }
-}
-
-#[cfg(test)]
-mod tests {
-    use crate::tests::fixtures;
-
-    use super::InodeData;
-    use super::InodeTracker;
-
-    /// Getting something non-existent should be none
-    #[test]
-    fn get_nonexistent() {
-        let inode_tracker = InodeTracker::default();
-        assert!(inode_tracker.get(1).is_none());
-    }
-
-    /// Put of a regular file should allocate a uid, which should be the same when inserting again.
-    #[test]
-    fn put_regular() {
-        let mut inode_tracker = InodeTracker::default();
-        let f = InodeData::Regular(
-            fixtures::BLOB_A_DIGEST.clone(),
-            fixtures::BLOB_A.len() as u64,
-            false,
-        );
-
-        // put it in
-        let ino = inode_tracker.put(f.clone());
-
-        // a get should return the right data
-        let data = inode_tracker.get(ino).expect("must be some");
-        match *data {
-            InodeData::Regular(ref digest, _, _) => {
-                assert_eq!(&fixtures::BLOB_A_DIGEST.clone(), digest);
-            }
-            InodeData::Symlink(_) | InodeData::Directory(..) => panic!("wrong type"),
-        }
-
-        // another put should return the same ino
-        assert_eq!(ino, inode_tracker.put(f));
-
-        // inserting another file should return a different ino
-        assert_ne!(
-            ino,
-            inode_tracker.put(InodeData::Regular(
-                fixtures::BLOB_B_DIGEST.clone(),
-                fixtures::BLOB_B.len() as u64,
-                false,
-            ))
-        );
-    }
-
-    // Put of a symlink should allocate a uid, which should be the same when inserting again
-    #[test]
-    fn put_symlink() {
-        let mut inode_tracker = InodeTracker::default();
-        let f = InodeData::Symlink("target".into());
-
-        // put it in
-        let ino = inode_tracker.put(f.clone());
-
-        // a get should return the right data
-        let data = inode_tracker.get(ino).expect("must be some");
-        match *data {
-            InodeData::Symlink(ref target) => {
-                assert_eq!(b"target".to_vec(), *target);
-            }
-            InodeData::Regular(..) | InodeData::Directory(..) => panic!("wrong type"),
-        }
-
-        // another put should return the same ino
-        assert_eq!(ino, inode_tracker.put(f));
-
-        // inserting another file should return a different ino
-        assert_ne!(ino, inode_tracker.put(InodeData::Symlink("target2".into())));
-    }
-}
diff --git a/tvix/store/src/fs/inodes.rs b/tvix/store/src/fs/inodes.rs
deleted file mode 100644
index 4047199982b2..000000000000
--- a/tvix/store/src/fs/inodes.rs
+++ /dev/null
@@ -1,57 +0,0 @@
-//! This module contains all the data structures used to track information
-//! about inodes, which present tvix-store nodes in a filesystem.
-use tvix_castore::proto as castorepb;
-use tvix_castore::B3Digest;
-
-#[derive(Clone, Debug)]
-pub enum InodeData {
-    Regular(B3Digest, u64, bool),  // digest, size, executable
-    Symlink(bytes::Bytes),         // target
-    Directory(DirectoryInodeData), // either [DirectoryInodeData:Sparse] or [DirectoryInodeData:Populated]
-}
-
-/// This encodes the two different states of [InodeData::Directory].
-/// Either the data still is sparse (we only saw a [castorepb::DirectoryNode],
-/// but didn't fetch the [castorepb::Directory] struct yet, or we processed a
-/// lookup and did fetch the data.
-#[derive(Clone, Debug)]
-pub enum DirectoryInodeData {
-    Sparse(B3Digest, u64),                                  // digest, size
-    Populated(B3Digest, Vec<(u64, castorepb::node::Node)>), // [(child_inode, node)]
-}
-
-impl From<&castorepb::node::Node> for InodeData {
-    fn from(value: &castorepb::node::Node) -> Self {
-        match value {
-            castorepb::node::Node::Directory(directory_node) => directory_node.into(),
-            castorepb::node::Node::File(file_node) => file_node.into(),
-            castorepb::node::Node::Symlink(symlink_node) => symlink_node.into(),
-        }
-    }
-}
-
-impl From<&castorepb::SymlinkNode> for InodeData {
-    fn from(value: &castorepb::SymlinkNode) -> Self {
-        InodeData::Symlink(value.target.clone())
-    }
-}
-
-impl From<&castorepb::FileNode> for InodeData {
-    fn from(value: &castorepb::FileNode) -> Self {
-        InodeData::Regular(
-            value.digest.clone().try_into().unwrap(),
-            value.size,
-            value.executable,
-        )
-    }
-}
-
-/// Converts a DirectoryNode to a sparsely populated InodeData::Directory.
-impl From<&castorepb::DirectoryNode> for InodeData {
-    fn from(value: &castorepb::DirectoryNode) -> Self {
-        InodeData::Directory(DirectoryInodeData::Sparse(
-            value.digest.clone().try_into().unwrap(),
-            value.size,
-        ))
-    }
-}
diff --git a/tvix/store/src/fs/mod.rs b/tvix/store/src/fs/mod.rs
deleted file mode 100644
index c11bd0a44c7e..000000000000
--- a/tvix/store/src/fs/mod.rs
+++ /dev/null
@@ -1,629 +0,0 @@
-mod file_attr;
-mod inode_tracker;
-mod inodes;
-mod root_nodes;
-
-#[cfg(feature = "fuse")]
-pub mod fuse;
-
-#[cfg(feature = "virtiofs")]
-pub mod virtiofs;
-
-#[cfg(test)]
-mod tests;
-
-use fuse_backend_rs::abi::fuse_abi::stat64;
-use fuse_backend_rs::api::filesystem::{Context, FileSystem, FsOptions, ROOT_ID};
-use futures::StreamExt;
-use parking_lot::RwLock;
-use std::ops::Deref;
-use std::{
-    collections::HashMap,
-    io,
-    sync::atomic::AtomicU64,
-    sync::{atomic::Ordering, Arc},
-    time::Duration,
-};
-use tokio::{
-    io::{AsyncReadExt, AsyncSeekExt},
-    sync::mpsc,
-};
-use tracing::{debug, info_span, instrument, warn};
-use tvix_castore::proto as castorepb;
-use tvix_castore::{
-    blobservice::{BlobReader, BlobService},
-    directoryservice::DirectoryService,
-    proto::{node::Node, NamedNode},
-    B3Digest,
-};
-
-use self::root_nodes::RootNodes;
-use self::{
-    file_attr::{gen_file_attr, ROOT_FILE_ATTR},
-    inode_tracker::InodeTracker,
-    inodes::{DirectoryInodeData, InodeData},
-};
-
-/// This implements a read-only FUSE filesystem for a tvix-store
-/// with the passed [BlobService], [DirectoryService] and [RootNodes].
-///
-/// Linux uses inodes in filesystems. When implementing FUSE, most calls are
-/// *for* a given inode.
-///
-/// This means, we need to have a stable mapping of inode numbers to the
-/// corresponding store nodes.
-///
-/// We internally delegate all inode allocation and state keeping to the
-/// inode tracker.
-/// We store a mapping from currently "explored" names in the root to their
-/// inode.
-///
-/// There's some places where inodes are allocated / data inserted into
-/// the inode tracker, if not allocated before already:
-///  - Processing a `lookup` request, either in the mount root, or somewhere
-///    deeper.
-///  - Processing a `readdir` request
-///
-///  Things pointing to the same contents get the same inodes, irrespective of
-///  their own location.
-///  This means:
-///  - Symlinks with the same target will get the same inode.
-///  - Regular/executable files with the same contents will get the same inode
-///  - Directories with the same contents will get the same inode.
-///
-/// Due to the above being valid across the whole store, and considering the
-/// merkle structure is a DAG, not a tree, this also means we can't do "bucketed
-/// allocation", aka reserve Directory.size inodes for each directory node we
-/// explore.
-pub struct TvixStoreFs<BS, DS, RN> {
-    blob_service: BS,
-    directory_service: DS,
-    root_nodes_provider: RN,
-
-    /// Whether to (try) listing elements in the root.
-    list_root: bool,
-
-    /// This maps a given basename in the root to the inode we allocated for the node.
-    root_nodes: RwLock<HashMap<Vec<u8>, u64>>,
-
-    /// This keeps track of inodes and data alongside them.
-    inode_tracker: RwLock<InodeTracker>,
-
-    /// This holds all open file handles
-    #[allow(clippy::type_complexity)]
-    file_handles: RwLock<HashMap<u64, Arc<tokio::sync::Mutex<Box<dyn BlobReader>>>>>,
-
-    next_file_handle: AtomicU64,
-
-    tokio_handle: tokio::runtime::Handle,
-}
-
-impl<BS, DS, RN> TvixStoreFs<BS, DS, RN>
-where
-    BS: Deref<Target = dyn BlobService> + Clone + Send,
-    DS: Deref<Target = dyn DirectoryService> + Clone + Send + 'static,
-    RN: RootNodes + Clone + 'static,
-{
-    pub fn new(
-        blob_service: BS,
-        directory_service: DS,
-        root_nodes_provider: RN,
-        list_root: bool,
-    ) -> Self {
-        Self {
-            blob_service,
-            directory_service,
-            root_nodes_provider,
-
-            list_root,
-
-            root_nodes: RwLock::new(HashMap::default()),
-            inode_tracker: RwLock::new(Default::default()),
-
-            file_handles: RwLock::new(Default::default()),
-            next_file_handle: AtomicU64::new(1),
-            tokio_handle: tokio::runtime::Handle::current(),
-        }
-    }
-
-    /// Retrieves the inode for a given root node basename, if present.
-    /// This obtains a read lock on self.root_nodes.
-    fn get_inode_for_root_name(&self, name: &[u8]) -> Option<u64> {
-        self.root_nodes.read().get(name).cloned()
-    }
-
-    /// For a given inode, look up the given directory behind it (from
-    /// self.inode_tracker), and return its children.
-    /// The inode_tracker MUST know about this inode already, and it MUST point
-    /// to a [InodeData::Directory].
-    /// It is ok if it's a [DirectoryInodeData::Sparse] - in that case, a lookup
-    /// in self.directory_service is performed, and self.inode_tracker is updated with the
-    /// [DirectoryInodeData::Populated].
-    #[instrument(skip(self), err)]
-    fn get_directory_children(&self, ino: u64) -> io::Result<(B3Digest, Vec<(u64, Node)>)> {
-        let data = self.inode_tracker.read().get(ino).unwrap();
-        match *data {
-            // if it's populated already, return children.
-            InodeData::Directory(DirectoryInodeData::Populated(
-                ref parent_digest,
-                ref children,
-            )) => Ok((parent_digest.clone(), children.clone())),
-            // if it's sparse, fetch data using directory_service, populate child nodes
-            // and update it in [self.inode_tracker].
-            InodeData::Directory(DirectoryInodeData::Sparse(ref parent_digest, _)) => {
-                let directory = self
-                    .tokio_handle
-                    .block_on(self.tokio_handle.spawn({
-                        let directory_service = self.directory_service.clone();
-                        let parent_digest = parent_digest.to_owned();
-                        async move { directory_service.get(&parent_digest).await }
-                    }))
-                    .unwrap()?
-                    .ok_or_else(|| {
-                        warn!(directory.digest=%parent_digest, "directory not found");
-                        // If the Directory can't be found, this is a hole, bail out.
-                        io::Error::from_raw_os_error(libc::EIO)
-                    })?;
-
-                // Turn the retrieved directory into a InodeData::Directory(DirectoryInodeData::Populated(..)),
-                // allocating inodes for the children on the way.
-                let children = {
-                    let mut inode_tracker = self.inode_tracker.write();
-
-                    let children: Vec<(u64, castorepb::node::Node)> = directory
-                        .nodes()
-                        .map(|child_node| {
-                            let child_ino = inode_tracker.put((&child_node).into());
-                            (child_ino, child_node)
-                        })
-                        .collect();
-
-                    // replace.
-                    inode_tracker.replace(
-                        ino,
-                        Arc::new(InodeData::Directory(DirectoryInodeData::Populated(
-                            parent_digest.clone(),
-                            children.clone(),
-                        ))),
-                    );
-
-                    children
-                };
-
-                Ok((parent_digest.clone(), children))
-            }
-            // if the parent inode was not a directory, this doesn't make sense
-            InodeData::Regular(..) | InodeData::Symlink(_) => {
-                Err(io::Error::from_raw_os_error(libc::ENOTDIR))
-            }
-        }
-    }
-
-    /// This will turn a lookup request for a name in the root to a ino and
-    /// [InodeData].
-    /// It will peek in [self.root_nodes], and then either look it up from
-    /// [self.inode_tracker],
-    /// or otherwise fetch from [self.root_nodes], and then insert into
-    /// [self.inode_tracker].
-    /// In the case the name can't be found, a libc::ENOENT is returned.
-    fn name_in_root_to_ino_and_data(
-        &self,
-        name: &std::ffi::CStr,
-    ) -> io::Result<(u64, Arc<InodeData>)> {
-        // Look up the inode for that root node.
-        // If there's one, [self.inode_tracker] MUST also contain the data,
-        // which we can then return.
-        if let Some(inode) = self.get_inode_for_root_name(name.to_bytes()) {
-            return Ok((
-                inode,
-                self.inode_tracker
-                    .read()
-                    .get(inode)
-                    .expect("must exist")
-                    .to_owned(),
-            ));
-        }
-
-        // We don't have it yet, look it up in [self.root_nodes].
-        match self.tokio_handle.block_on({
-            let root_nodes_provider = self.root_nodes_provider.clone();
-            async move { root_nodes_provider.get_by_basename(name.to_bytes()).await }
-        }) {
-            // if there was an error looking up the root node, propagate up an IO error.
-            Err(_e) => Err(io::Error::from_raw_os_error(libc::EIO)),
-            // the root node doesn't exist, so the file doesn't exist.
-            Ok(None) => Err(io::Error::from_raw_os_error(libc::ENOENT)),
-            // The root node does exist
-            Ok(Some(root_node)) => {
-                // The name must match what's passed in the lookup, otherwise this is also a ENOENT.
-                if root_node.get_name() != name.to_bytes() {
-                    debug!(root_node.name=?root_node.get_name(), found_node.name=%name.to_string_lossy(), "node name mismatch");
-                    return Err(io::Error::from_raw_os_error(libc::ENOENT));
-                }
-
-                // Let's check if someone else beat us to updating the inode tracker and
-                // root_nodes map. This avoids locking inode_tracker for writing.
-                if let Some(ino) = self.root_nodes.read().get(name.to_bytes()) {
-                    return Ok((
-                        *ino,
-                        self.inode_tracker.read().get(*ino).expect("must exist"),
-                    ));
-                }
-
-                // Only in case it doesn't, lock [self.root_nodes] and
-                // [self.inode_tracker] for writing.
-                let mut root_nodes = self.root_nodes.write();
-                let mut inode_tracker = self.inode_tracker.write();
-
-                // insert the (sparse) inode data and register in
-                // self.root_nodes.
-                let inode_data: InodeData = (&root_node).into();
-                let ino = inode_tracker.put(inode_data.clone());
-                root_nodes.insert(name.to_bytes().into(), ino);
-
-                Ok((ino, Arc::new(inode_data)))
-            }
-        }
-    }
-}
-
-impl<BS, DS, RN> FileSystem for TvixStoreFs<BS, DS, RN>
-where
-    BS: Deref<Target = dyn BlobService> + Clone + Send + 'static,
-    DS: Deref<Target = dyn DirectoryService> + Send + Clone + 'static,
-    RN: RootNodes + Clone + 'static,
-{
-    type Handle = u64;
-    type Inode = u64;
-
-    fn init(&self, _capable: FsOptions) -> io::Result<FsOptions> {
-        Ok(FsOptions::empty())
-    }
-
-    #[tracing::instrument(skip_all, fields(rq.inode = inode))]
-    fn getattr(
-        &self,
-        _ctx: &Context,
-        inode: Self::Inode,
-        _handle: Option<Self::Handle>,
-    ) -> io::Result<(stat64, Duration)> {
-        if inode == ROOT_ID {
-            return Ok((ROOT_FILE_ATTR.into(), Duration::MAX));
-        }
-
-        match self.inode_tracker.read().get(inode) {
-            None => Err(io::Error::from_raw_os_error(libc::ENOENT)),
-            Some(node) => {
-                debug!(node = ?node, "found node");
-                Ok((gen_file_attr(&node, inode).into(), Duration::MAX))
-            }
-        }
-    }
-
-    #[tracing::instrument(skip_all, fields(rq.parent_inode = parent, rq.name = ?name))]
-    fn lookup(
-        &self,
-        _ctx: &Context,
-        parent: Self::Inode,
-        name: &std::ffi::CStr,
-    ) -> io::Result<fuse_backend_rs::api::filesystem::Entry> {
-        debug!("lookup");
-
-        // This goes from a parent inode to a node.
-        // - If the parent is [ROOT_ID], we need to check
-        //   [self.root_nodes] (fetching from a [RootNode] provider if needed)
-        // - Otherwise, lookup the parent in [self.inode_tracker] (which must be
-        //   a [InodeData::Directory]), and find the child with that name.
-        if parent == ROOT_ID {
-            let (ino, inode_data) = self.name_in_root_to_ino_and_data(name)?;
-
-            debug!(inode_data=?&inode_data, ino=ino, "Some");
-            return Ok(fuse_backend_rs::api::filesystem::Entry {
-                inode: ino,
-                attr: gen_file_attr(&inode_data, ino).into(),
-                attr_timeout: Duration::MAX,
-                entry_timeout: Duration::MAX,
-                ..Default::default()
-            });
-        }
-        // This is the "lookup for "a" inside inode 42.
-        // We already know that inode 42 must be a directory.
-        let (parent_digest, children) = self.get_directory_children(parent)?;
-
-        let span = info_span!("lookup", directory.digest = %parent_digest);
-        let _enter = span.enter();
-
-        // Search for that name in the list of children and return the FileAttrs.
-
-        // in the children, find the one with the desired name.
-        if let Some((child_ino, _)) = children.iter().find(|e| e.1.get_name() == name.to_bytes()) {
-            // lookup the child [InodeData] in [self.inode_tracker].
-            // We know the inodes for children have already been allocated.
-            let child_inode_data = self.inode_tracker.read().get(*child_ino).unwrap();
-
-            // Reply with the file attributes for the child.
-            // For child directories, we still have all data we need to reply.
-            Ok(fuse_backend_rs::api::filesystem::Entry {
-                inode: *child_ino,
-                attr: gen_file_attr(&child_inode_data, *child_ino).into(),
-                attr_timeout: Duration::MAX,
-                entry_timeout: Duration::MAX,
-                ..Default::default()
-            })
-        } else {
-            // Child not found, return ENOENT.
-            Err(io::Error::from_raw_os_error(libc::ENOENT))
-        }
-    }
-
-    // TODO: readdirplus?
-
-    #[tracing::instrument(skip_all, fields(rq.inode = inode, rq.offset = offset))]
-    fn readdir(
-        &self,
-        _ctx: &Context,
-        inode: Self::Inode,
-        _handle: Self::Handle,
-        _size: u32,
-        offset: u64,
-        add_entry: &mut dyn FnMut(fuse_backend_rs::api::filesystem::DirEntry) -> io::Result<usize>,
-    ) -> io::Result<()> {
-        debug!("readdir");
-
-        if inode == ROOT_ID {
-            if !self.list_root {
-                return Err(io::Error::from_raw_os_error(libc::EPERM)); // same error code as ipfs/kubo
-            } else {
-                let root_nodes_provider = self.root_nodes_provider.clone();
-                let (tx, mut rx) = mpsc::channel(16);
-
-                // This task will run in the background immediately and will exit
-                // after the stream ends or if we no longer want any more entries.
-                self.tokio_handle.spawn(async move {
-                    let mut stream = root_nodes_provider.list().skip(offset as usize).enumerate();
-                    while let Some(node) = stream.next().await {
-                        if tx.send(node).await.is_err() {
-                            // If we get a send error, it means the sync code
-                            // doesn't want any more entries.
-                            break;
-                        }
-                    }
-                });
-
-                while let Some((i, root_node)) = rx.blocking_recv() {
-                    let root_node = match root_node {
-                        Err(e) => {
-                            warn!("failed to retrieve pathinfo: {}", e);
-                            return Err(io::Error::from_raw_os_error(libc::EPERM));
-                        }
-                        Ok(root_node) => root_node,
-                    };
-
-                    let name = root_node.get_name();
-                    // obtain the inode, or allocate a new one.
-                    let ino = self.get_inode_for_root_name(name).unwrap_or_else(|| {
-                        // insert the (sparse) inode data and register in
-                        // self.root_nodes.
-                        let ino = self.inode_tracker.write().put((&root_node).into());
-                        self.root_nodes.write().insert(name.into(), ino);
-                        ino
-                    });
-
-                    let ty = match root_node {
-                        Node::Directory(_) => libc::S_IFDIR,
-                        Node::File(_) => libc::S_IFREG,
-                        Node::Symlink(_) => libc::S_IFLNK,
-                    };
-
-                    let written = add_entry(fuse_backend_rs::api::filesystem::DirEntry {
-                        ino,
-                        offset: offset + i as u64 + 1,
-                        type_: ty,
-                        name,
-                    })?;
-                    // If the buffer is full, add_entry will return `Ok(0)`.
-                    if written == 0 {
-                        break;
-                    }
-                }
-
-                return Ok(());
-            }
-        }
-
-        // lookup the children, or return an error if it's not a directory.
-        let (parent_digest, children) = self.get_directory_children(inode)?;
-
-        let span = info_span!("lookup", directory.digest = %parent_digest);
-        let _enter = span.enter();
-
-        for (i, (ino, child_node)) in children.iter().skip(offset as usize).enumerate() {
-            // the second parameter will become the "offset" parameter on the next call.
-            let written = add_entry(fuse_backend_rs::api::filesystem::DirEntry {
-                ino: *ino,
-                offset: offset + i as u64 + 1,
-                type_: match child_node {
-                    #[allow(clippy::unnecessary_cast)]
-                    // libc::S_IFDIR is u32 on Linux and u16 on MacOS
-                    Node::Directory(_) => libc::S_IFDIR as u32,
-                    #[allow(clippy::unnecessary_cast)]
-                    // libc::S_IFDIR is u32 on Linux and u16 on MacOS
-                    Node::File(_) => libc::S_IFREG as u32,
-                    #[allow(clippy::unnecessary_cast)]
-                    // libc::S_IFDIR is u32 on Linux and u16 on MacOS
-                    Node::Symlink(_) => libc::S_IFLNK as u32,
-                },
-                name: child_node.get_name(),
-            })?;
-            // If the buffer is full, add_entry will return `Ok(0)`.
-            if written == 0 {
-                break;
-            }
-        }
-
-        Ok(())
-    }
-
-    #[tracing::instrument(skip_all, fields(rq.inode = inode))]
-    fn open(
-        &self,
-        _ctx: &Context,
-        inode: Self::Inode,
-        _flags: u32,
-        _fuse_flags: u32,
-    ) -> io::Result<(
-        Option<Self::Handle>,
-        fuse_backend_rs::api::filesystem::OpenOptions,
-    )> {
-        if inode == ROOT_ID {
-            return Err(io::Error::from_raw_os_error(libc::ENOSYS));
-        }
-
-        // lookup the inode
-        match *self.inode_tracker.read().get(inode).unwrap() {
-            // read is invalid on non-files.
-            InodeData::Directory(..) | InodeData::Symlink(_) => {
-                warn!("is directory");
-                Err(io::Error::from_raw_os_error(libc::EISDIR))
-            }
-            InodeData::Regular(ref blob_digest, _blob_size, _) => {
-                let span = info_span!("read", blob.digest = %blob_digest);
-                let _enter = span.enter();
-
-                let blob_service = self.blob_service.clone();
-                let blob_digest = blob_digest.clone();
-
-                let task = self
-                    .tokio_handle
-                    .spawn(async move { blob_service.open_read(&blob_digest).await });
-
-                let blob_reader = self.tokio_handle.block_on(task).unwrap();
-
-                match blob_reader {
-                    Ok(None) => {
-                        warn!("blob not found");
-                        Err(io::Error::from_raw_os_error(libc::EIO))
-                    }
-                    Err(e) => {
-                        warn!(e=?e, "error opening blob");
-                        Err(io::Error::from_raw_os_error(libc::EIO))
-                    }
-                    Ok(Some(blob_reader)) => {
-                        // get a new file handle
-                        // TODO: this will overflow after 2**64 operations,
-                        // which is fine for now.
-                        // See https://cl.tvl.fyi/c/depot/+/8834/comment/a6684ce0_d72469d1
-                        // for the discussion on alternatives.
-                        let fh = self.next_file_handle.fetch_add(1, Ordering::SeqCst);
-
-                        debug!("add file handle {}", fh);
-                        self.file_handles
-                            .write()
-                            .insert(fh, Arc::new(tokio::sync::Mutex::new(blob_reader)));
-
-                        Ok((
-                            Some(fh),
-                            fuse_backend_rs::api::filesystem::OpenOptions::empty(),
-                        ))
-                    }
-                }
-            }
-        }
-    }
-
-    #[tracing::instrument(skip_all, fields(rq.inode = inode, fh = handle))]
-    fn release(
-        &self,
-        _ctx: &Context,
-        inode: Self::Inode,
-        _flags: u32,
-        handle: Self::Handle,
-        _flush: bool,
-        _flock_release: bool,
-        _lock_owner: Option<u64>,
-    ) -> io::Result<()> {
-        // remove and get ownership on the blob reader
-        match self.file_handles.write().remove(&handle) {
-            // drop it, which will close it.
-            Some(blob_reader) => drop(blob_reader),
-            None => {
-                // These might already be dropped if a read error occured.
-                debug!("file_handle {} not found", handle);
-            }
-        }
-
-        Ok(())
-    }
-
-    #[tracing::instrument(skip_all, fields(rq.inode = inode, rq.offset = offset, rq.size = size))]
-    fn read(
-        &self,
-        _ctx: &Context,
-        inode: Self::Inode,
-        handle: Self::Handle,
-        w: &mut dyn fuse_backend_rs::api::filesystem::ZeroCopyWriter,
-        size: u32,
-        offset: u64,
-        _lock_owner: Option<u64>,
-        _flags: u32,
-    ) -> io::Result<usize> {
-        debug!("read");
-
-        // We need to take out the blob reader from self.file_handles, so we can
-        // interact with it in the separate task.
-        // On success, we pass it back out of the task, so we can put it back in self.file_handles.
-        let blob_reader = match self.file_handles.read().get(&handle) {
-            Some(blob_reader) => blob_reader.clone(),
-            None => {
-                warn!("file handle {} unknown", handle);
-                return Err(io::Error::from_raw_os_error(libc::EIO));
-            }
-        };
-
-        let task = self.tokio_handle.spawn(async move {
-            let mut blob_reader = blob_reader.lock().await;
-
-            // seek to the offset specified, which is relative to the start of the file.
-            let resp = blob_reader.seek(io::SeekFrom::Start(offset)).await;
-
-            match resp {
-                Ok(pos) => {
-                    debug_assert_eq!(offset, pos);
-                }
-                Err(e) => {
-                    warn!("failed to seek to offset {}: {}", offset, e);
-                    return Err(io::Error::from_raw_os_error(libc::EIO));
-                }
-            }
-
-            // As written in the fuse docs, read should send exactly the number
-            // of bytes requested except on EOF or error.
-
-            let mut buf: Vec<u8> = Vec::with_capacity(size as usize);
-
-            // copy things from the internal buffer into buf to fill it till up until size
-            tokio::io::copy(&mut blob_reader.as_mut().take(size as u64), &mut buf).await?;
-
-            Ok(buf)
-        });
-
-        let buf = self.tokio_handle.block_on(task).unwrap()?;
-
-        w.write(&buf)
-    }
-
-    #[tracing::instrument(skip_all, fields(rq.inode = inode))]
-    fn readlink(&self, _ctx: &Context, inode: Self::Inode) -> io::Result<Vec<u8>> {
-        if inode == ROOT_ID {
-            return Err(io::Error::from_raw_os_error(libc::ENOSYS));
-        }
-
-        // lookup the inode
-        match *self.inode_tracker.read().get(inode).unwrap() {
-            InodeData::Directory(..) | InodeData::Regular(..) => {
-                Err(io::Error::from_raw_os_error(libc::EINVAL))
-            }
-            InodeData::Symlink(ref target) => Ok(target.to_vec()),
-        }
-    }
-}
diff --git a/tvix/store/src/fs/root_nodes.rs b/tvix/store/src/fs/root_nodes.rs
deleted file mode 100644
index e672c6e647f3..000000000000
--- a/tvix/store/src/fs/root_nodes.rs
+++ /dev/null
@@ -1,61 +0,0 @@
-use std::{ops::Deref, pin::Pin};
-
-use futures::{Stream, StreamExt};
-use nix_compat::store_path::StorePath;
-use tonic::async_trait;
-use tvix_castore::{proto::node::Node, Error};
-
-use crate::pathinfoservice::PathInfoService;
-
-/// Provides an interface for looking up root nodes  in tvix-castore by given
-/// a lookup key (usually the basename), and optionally allow a listing.
-///
-#[async_trait]
-pub trait RootNodes: Send + Sync {
-    /// Looks up a root CA node based on the basename of the node in the root
-    /// directory of the filesystem.
-    async fn get_by_basename(&self, name: &[u8]) -> Result<Option<Node>, Error>;
-
-    /// Lists all root CA nodes in the filesystem. An error can be returned
-    /// in case listing is not allowed
-    fn list(&self) -> Pin<Box<dyn Stream<Item = Result<Node, Error>> + Send>>;
-}
-
-/// Implements root node lookup for any [PathInfoService]. This represents a flat
-/// directory structure like /nix/store where each entry in the root filesystem
-/// directory corresponds to a CA node.
-#[async_trait]
-impl<T> RootNodes for T
-where
-    T: Deref<Target = dyn PathInfoService> + Send + Sync,
-{
-    async fn get_by_basename(&self, name: &[u8]) -> Result<Option<Node>, Error> {
-        let Ok(store_path) = StorePath::from_bytes(name) else {
-            return Ok(None);
-        };
-
-        Ok(self
-            .deref()
-            .get(*store_path.digest())
-            .await?
-            .map(|path_info| {
-                path_info
-                    .node
-                    .expect("missing root node")
-                    .node
-                    .expect("empty node")
-            }))
-    }
-
-    fn list(&self) -> Pin<Box<dyn Stream<Item = Result<Node, Error>> + Send>> {
-        Box::pin(self.deref().list().map(|result| {
-            result.map(|path_info| {
-                path_info
-                    .node
-                    .expect("missing root node")
-                    .node
-                    .expect("empty node")
-            })
-        }))
-    }
-}
diff --git a/tvix/store/src/fs/virtiofs.rs b/tvix/store/src/fs/virtiofs.rs
deleted file mode 100644
index 846270d28568..000000000000
--- a/tvix/store/src/fs/virtiofs.rs
+++ /dev/null
@@ -1,237 +0,0 @@
-use std::{
-    convert, error, fmt, io,
-    ops::Deref,
-    path::Path,
-    sync::{Arc, MutexGuard, RwLock},
-};
-
-use fuse_backend_rs::{
-    api::{filesystem::FileSystem, server::Server},
-    transport::{FsCacheReqHandler, Reader, VirtioFsWriter},
-};
-use tracing::error;
-use vhost::vhost_user::{
-    Listener, SlaveFsCacheReq, VhostUserProtocolFeatures, VhostUserVirtioFeatures,
-};
-use vhost_user_backend::{VhostUserBackendMut, VhostUserDaemon, VringMutex, VringState, VringT};
-use virtio_bindings::bindings::virtio_ring::{
-    VIRTIO_RING_F_EVENT_IDX, VIRTIO_RING_F_INDIRECT_DESC,
-};
-use virtio_queue::QueueT;
-use vm_memory::{GuestAddressSpace, GuestMemoryAtomic, GuestMemoryMmap};
-use vmm_sys_util::epoll::EventSet;
-
-const VIRTIO_F_VERSION_1: u32 = 32;
-const NUM_QUEUES: usize = 2;
-const QUEUE_SIZE: usize = 1024;
-
-#[derive(Debug)]
-enum Error {
-    /// Failed to handle non-input event.
-    HandleEventNotEpollIn,
-    /// Failed to handle unknown event.
-    HandleEventUnknownEvent,
-    /// Invalid descriptor chain.
-    InvalidDescriptorChain,
-    /// Failed to handle filesystem requests.
-    HandleRequests(fuse_backend_rs::Error),
-    /// Failed to construct new vhost user daemon.
-    NewDaemon,
-    /// Failed to start the vhost user daemon.
-    StartDaemon,
-    /// Failed to wait for the vhost user daemon.
-    WaitDaemon,
-}
-
-impl fmt::Display for Error {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "vhost_user_fs_error: {self:?}")
-    }
-}
-
-impl error::Error for Error {}
-
-impl convert::From<Error> for io::Error {
-    fn from(e: Error) -> Self {
-        io::Error::new(io::ErrorKind::Other, e)
-    }
-}
-
-struct VhostUserFsBackend<FS>
-where
-    FS: FileSystem + Send + Sync,
-{
-    server: Arc<Server<Arc<FS>>>,
-    event_idx: bool,
-    guest_mem: GuestMemoryAtomic<GuestMemoryMmap>,
-    cache_req: Option<SlaveFsCacheReq>,
-}
-
-impl<FS> VhostUserFsBackend<FS>
-where
-    FS: FileSystem + Send + Sync,
-{
-    fn process_queue(&mut self, vring: &mut MutexGuard<VringState>) -> std::io::Result<bool> {
-        let mut used_descs = false;
-
-        while let Some(desc_chain) = vring
-            .get_queue_mut()
-            .pop_descriptor_chain(self.guest_mem.memory())
-        {
-            let memory = desc_chain.memory();
-            let reader = Reader::from_descriptor_chain(memory, desc_chain.clone())
-                .map_err(|_| Error::InvalidDescriptorChain)?;
-            let writer = VirtioFsWriter::new(memory, desc_chain.clone())
-                .map_err(|_| Error::InvalidDescriptorChain)?;
-
-            self.server
-                .handle_message(
-                    reader,
-                    writer.into(),
-                    self.cache_req
-                        .as_mut()
-                        .map(|req| req as &mut dyn FsCacheReqHandler),
-                    None,
-                )
-                .map_err(Error::HandleRequests)?;
-
-            // TODO: Is len 0 correct?
-            if let Err(error) = vring
-                .get_queue_mut()
-                .add_used(memory, desc_chain.head_index(), 0)
-            {
-                error!(?error, "failed to add desc back to ring");
-            }
-
-            // TODO: What happens if we error out before here?
-            used_descs = true;
-        }
-
-        let needs_notification = if self.event_idx {
-            match vring
-                .get_queue_mut()
-                .needs_notification(self.guest_mem.memory().deref())
-            {
-                Ok(needs_notification) => needs_notification,
-                Err(error) => {
-                    error!(?error, "failed to check if queue needs notification");
-                    true
-                }
-            }
-        } else {
-            true
-        };
-
-        if needs_notification {
-            if let Err(error) = vring.signal_used_queue() {
-                error!(?error, "failed to signal used queue");
-            }
-        }
-
-        Ok(used_descs)
-    }
-}
-
-impl<FS> VhostUserBackendMut<VringMutex> for VhostUserFsBackend<FS>
-where
-    FS: FileSystem + Send + Sync,
-{
-    fn num_queues(&self) -> usize {
-        NUM_QUEUES
-    }
-
-    fn max_queue_size(&self) -> usize {
-        QUEUE_SIZE
-    }
-
-    fn features(&self) -> u64 {
-        1 << VIRTIO_F_VERSION_1
-            | 1 << VIRTIO_RING_F_INDIRECT_DESC
-            | 1 << VIRTIO_RING_F_EVENT_IDX
-            | VhostUserVirtioFeatures::PROTOCOL_FEATURES.bits()
-    }
-
-    fn protocol_features(&self) -> VhostUserProtocolFeatures {
-        VhostUserProtocolFeatures::MQ | VhostUserProtocolFeatures::SLAVE_REQ
-    }
-
-    fn set_event_idx(&mut self, enabled: bool) {
-        self.event_idx = enabled;
-    }
-
-    fn update_memory(&mut self, _mem: GuestMemoryAtomic<GuestMemoryMmap>) -> std::io::Result<()> {
-        // This is what most the vhost user implementations do...
-        Ok(())
-    }
-
-    fn set_slave_req_fd(&mut self, cache_req: SlaveFsCacheReq) {
-        self.cache_req = Some(cache_req);
-    }
-
-    fn handle_event(
-        &mut self,
-        device_event: u16,
-        evset: vmm_sys_util::epoll::EventSet,
-        vrings: &[VringMutex],
-        _thread_id: usize,
-    ) -> std::io::Result<bool> {
-        if evset != EventSet::IN {
-            return Err(Error::HandleEventNotEpollIn.into());
-        }
-
-        let mut queue = match device_event {
-            // High priority queue
-            0 => vrings[0].get_mut(),
-            // Regurlar priority queue
-            1 => vrings[1].get_mut(),
-            _ => {
-                return Err(Error::HandleEventUnknownEvent.into());
-            }
-        };
-
-        if self.event_idx {
-            loop {
-                queue
-                    .get_queue_mut()
-                    .enable_notification(self.guest_mem.memory().deref())
-                    .map_err(|e| io::Error::new(io::ErrorKind::Other, e.to_string()))?;
-                if !self.process_queue(&mut queue)? {
-                    break;
-                }
-            }
-        } else {
-            self.process_queue(&mut queue)?;
-        }
-
-        Ok(false)
-    }
-}
-
-pub fn start_virtiofs_daemon<FS, P>(fs: FS, socket: P) -> io::Result<()>
-where
-    FS: FileSystem + Send + Sync + 'static,
-    P: AsRef<Path>,
-{
-    let guest_mem = GuestMemoryAtomic::new(GuestMemoryMmap::new());
-
-    let server = Arc::new(fuse_backend_rs::api::server::Server::new(Arc::new(fs)));
-
-    let backend = Arc::new(RwLock::new(VhostUserFsBackend {
-        server,
-        guest_mem: guest_mem.clone(),
-        event_idx: false,
-        cache_req: None,
-    }));
-
-    let listener = Listener::new(socket, true).unwrap();
-
-    let mut fs_daemon =
-        VhostUserDaemon::new(String::from("vhost-user-fs-tvix-store"), backend, guest_mem)
-            .map_err(|_| Error::NewDaemon)?;
-
-    fs_daemon.start(listener).map_err(|_| Error::StartDaemon)?;
-
-    fs_daemon.wait().map_err(|_| Error::WaitDaemon)?;
-
-    Ok(())
-}
diff --git a/tvix/store/src/lib.rs b/tvix/store/src/lib.rs
index c59121453352..5b57781c4dab 100644
--- a/tvix/store/src/lib.rs
+++ b/tvix/store/src/lib.rs
@@ -1,6 +1,3 @@
-#[cfg(feature = "fs")]
-pub mod fs;
-
 pub mod nar;
 pub mod pathinfoservice;
 pub mod proto;
diff --git a/tvix/store/src/pathinfoservice/fs/mod.rs b/tvix/store/src/pathinfoservice/fs/mod.rs
new file mode 100644
index 000000000000..524aa10391f8
--- /dev/null
+++ b/tvix/store/src/pathinfoservice/fs/mod.rs
@@ -0,0 +1,84 @@
+use futures::Stream;
+use futures::StreamExt;
+use std::ops::Deref;
+use std::pin::Pin;
+use tonic::async_trait;
+use tvix_castore::fs::{RootNodes, TvixStoreFs};
+use tvix_castore::proto as castorepb;
+use tvix_castore::Error;
+use tvix_castore::{blobservice::BlobService, directoryservice::DirectoryService};
+
+use super::PathInfoService;
+
+#[cfg(test)]
+mod tests;
+
+/// Helper to construct a [TvixStoreFs] from a [BlobService], [DirectoryService]
+/// and [PathInfoService].
+/// This avoids users to have to interact with the wrapper struct directly, as
+/// it leaks into the type signature of TvixStoreFS.
+pub fn make_fs<BS, DS, PS>(
+    blob_service: BS,
+    directory_service: DS,
+    path_info_service: PS,
+    list_root: bool,
+) -> TvixStoreFs<BS, DS, RootNodesWrapper<PS>>
+where
+    BS: Deref<Target = dyn BlobService> + Send + Clone + 'static,
+    DS: Deref<Target = dyn DirectoryService> + Send + Clone + 'static,
+    PS: Deref<Target = dyn PathInfoService> + Send + Sync + Clone + 'static,
+{
+    TvixStoreFs::new(
+        blob_service,
+        directory_service,
+        RootNodesWrapper(path_info_service),
+        list_root,
+    )
+}
+
+/// Wrapper to satisfy Rust's orphan rules for trait implementations, as
+/// RootNodes is coming from the [tvix-castore] crate.
+#[doc(hidden)]
+#[derive(Clone, Debug)]
+pub struct RootNodesWrapper<T>(pub(crate) T);
+
+/// Implements root node lookup for any [PathInfoService]. This represents a flat
+/// directory structure like /nix/store where each entry in the root filesystem
+/// directory corresponds to a CA node.
+#[cfg(any(feature = "fuse", feature = "virtiofs"))]
+#[async_trait]
+impl<T> RootNodes for RootNodesWrapper<T>
+where
+    T: Deref<Target = dyn PathInfoService> + Send + Sync,
+{
+    async fn get_by_basename(&self, name: &[u8]) -> Result<Option<castorepb::node::Node>, Error> {
+        let Ok(store_path) = nix_compat::store_path::StorePath::from_bytes(name) else {
+            return Ok(None);
+        };
+
+        Ok(self
+            .0
+            .deref()
+            .get(*store_path.digest())
+            .await?
+            .map(|path_info| {
+                path_info
+                    .node
+                    .expect("missing root node")
+                    .node
+                    .expect("empty node")
+            }))
+    }
+
+    fn list(&self) -> Pin<Box<dyn Stream<Item = Result<castorepb::node::Node, Error>> + Send>> {
+        Box::pin(self.0.deref().list().map(|result| {
+            result.map(|path_info| {
+                path_info
+                    .node
+                    .expect("missing root node")
+                    .node
+                    .expect("empty node")
+            })
+        }))
+    }
+}
diff --git a/tvix/store/src/fs/tests.rs b/tvix/store/src/pathinfoservice/fs/tests.rs
index a3977c727505..d12ee2f2a03e 100644
--- a/tvix/store/src/fs/tests.rs
+++ b/tvix/store/src/pathinfoservice/fs/tests.rs
@@ -1,22 +1,22 @@
+use crate::pathinfoservice::PathInfoService;
+use crate::proto::PathInfo;
+use crate::tests::fixtures;
+use crate::tests::utils::{gen_blob_service, gen_directory_service, gen_pathinfo_service};
 use futures::StreamExt;
 use std::io::Cursor;
 use std::os::unix::prelude::MetadataExt;
 use std::path::Path;
 use std::sync::Arc;
+use tempfile::TempDir;
 use tokio::{fs, io};
 use tokio_stream::wrappers::ReadDirStream;
 use tvix_castore::blobservice::BlobService;
 use tvix_castore::directoryservice::DirectoryService;
-
-use tempfile::TempDir;
-
-use crate::fs::{fuse::FuseDaemon, TvixStoreFs};
-use crate::pathinfoservice::PathInfoService;
-use crate::proto::PathInfo;
-use crate::tests::fixtures;
-use crate::tests::utils::{gen_blob_service, gen_directory_service, gen_pathinfo_service};
+use tvix_castore::fs::fuse::FuseDaemon;
 use tvix_castore::proto as castorepb;
 
+use super::make_fs;
+
 const BLOB_A_NAME: &str = "00000000000000000000000000000000-test";
 const BLOB_B_NAME: &str = "55555555555555555555555555555555-test";
 const HELLOWORLD_BLOB_NAME: &str = "66666666666666666666666666666666-test";
@@ -44,7 +44,7 @@ fn do_mount<P: AsRef<Path>>(
     mountpoint: P,
     list_root: bool,
 ) -> io::Result<FuseDaemon> {
-    let fs = TvixStoreFs::new(
+    let fs = make_fs(
         blob_service,
         directory_service,
         path_info_service,
diff --git a/tvix/store/src/pathinfoservice/mod.rs b/tvix/store/src/pathinfoservice/mod.rs
index 5faa0900a0b0..3bd0ef206998 100644
--- a/tvix/store/src/pathinfoservice/mod.rs
+++ b/tvix/store/src/pathinfoservice/mod.rs
@@ -4,6 +4,9 @@ mod memory;
 mod nix_http;
 mod sled;
 
+#[cfg(any(feature = "fuse", feature = "virtiofs"))]
+mod fs;
+
 use futures::Stream;
 use std::pin::Pin;
 use tonic::async_trait;
@@ -18,6 +21,9 @@ pub use self::memory::MemoryPathInfoService;
 pub use self::nix_http::NixHTTPPathInfoService;
 pub use self::sled::SledPathInfoService;
 
+#[cfg(any(feature = "fuse", feature = "virtiofs"))]
+pub use self::fs::make_fs;
+
 /// The base trait all PathInfo services need to implement.
 #[async_trait]
 pub trait PathInfoService: Send + Sync {