feat(tvix/store/fuse): allow listing r/6556

This provides an additional configuration flag to the tvix-store mount
subcommand, and logic in the fuse module to request listing for the
root of the mountpoint.

Change-Id: I05a8bc11f7991b574696f27a30afe0f4e718a58c
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9217
Autosubmit: flokli <flokli@flokli.de>
Reviewed-by: adisbladis <adisbladis@gmail.com>
Tested-by: BuildkiteCI

3 files changed, 111 insertions, 4 deletions

diff --git a/tvix/store/src/bin/tvix-store.rs b/tvix/store/src/bin/tvix-store.rs
index 5b6c98e4ee45..d2a8927351f9 100644
--- a/tvix/store/src/bin/tvix-store.rs
+++ b/tvix/store/src/bin/tvix-store.rs
@@ -90,6 +90,10 @@ enum Commands {
 
         #[arg(long, env, default_value = "grpc+http://[::1]:8000")]
         path_info_service_addr: String,
+
+        /// Whether to list elements at the root of the mount point.
+        #[clap(long, short, action)]
+        list_root: bool,
     },
 }
 
@@ -250,6 +254,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
             blob_service_addr,
             directory_service_addr,
             path_info_service_addr,
+            list_root,
         } => {
             let blob_service = blobservice::from_addr(&blob_service_addr)?;
             let directory_service = directoryservice::from_addr(&directory_service_addr)?;
@@ -260,7 +265,12 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
             )?;
 
             tokio::task::spawn_blocking(move || {
-                let f = FUSE::new(blob_service, directory_service, path_info_service);
+                let f = FUSE::new(
+                    blob_service,
+                    directory_service,
+                    path_info_service,
+                    list_root,
+                );
                 fuser::mount2(f, &dest, &[])
             })
             .await??
diff --git a/tvix/store/src/fuse/mod.rs b/tvix/store/src/fuse/mod.rs
index 8b44f7db550e..0015abb9d557 100644
--- a/tvix/store/src/fuse/mod.rs
+++ b/tvix/store/src/fuse/mod.rs
@@ -66,6 +66,9 @@ pub struct FUSE {
     directory_service: Arc<dyn DirectoryService>,
     path_info_service: Arc<dyn PathInfoService>,
 
+    /// Whether to (try) listing elements in the root.
+    list_root: bool,
+
     /// This maps a given StorePath to the inode we allocated for the root inode.
     store_paths: HashMap<StorePath, u64>,
 
@@ -83,12 +86,15 @@ impl FUSE {
         blob_service: Arc<dyn BlobService>,
         directory_service: Arc<dyn DirectoryService>,
         path_info_service: Arc<dyn PathInfoService>,
+        list_root: bool,
     ) -> Self {
         Self {
             blob_service,
             directory_service,
             path_info_service,
 
+            list_root,
+
             store_paths: HashMap::default(),
             inode_tracker: Default::default(),
 
@@ -311,8 +317,55 @@ impl fuser::Filesystem for FUSE {
         debug!("readdir");
 
         if ino == fuser::FUSE_ROOT_ID {
-            reply.error(libc::EPERM); // same error code as ipfs/kubo
-            return;
+            if !self.list_root {
+                reply.error(libc::EPERM); // same error code as ipfs/kubo
+                return;
+            } else {
+                for (i, path_info) in self
+                    .path_info_service
+                    .list()
+                    .skip(offset as usize)
+                    .enumerate()
+                {
+                    let path_info = match path_info {
+                        Err(e) => {
+                            warn!("failed to retrieve pathinfo: {}", e);
+                            reply.error(libc::EPERM);
+                            return;
+                        }
+                        Ok(path_info) => path_info,
+                    };
+
+                    // We know the root node exists and the store_path can be parsed because clients MUST validate.
+                    let root_node = path_info.node.unwrap().node.unwrap();
+                    let store_path = StorePath::from_bytes(root_node.get_name()).unwrap();
+
+                    let ino = match self.store_paths.get(&store_path) {
+                        Some(ino) => *ino,
+                        None => {
+                            // insert the (sparse) inode data and register in
+                            // self.store_paths.
+                            let ino = self.inode_tracker.put((&root_node).into());
+                            self.store_paths.insert(store_path.clone(), ino);
+                            ino
+                        }
+                    };
+
+                    let ty = match root_node {
+                        Node::Directory(_) => fuser::FileType::Directory,
+                        Node::File(_) => fuser::FileType::RegularFile,
+                        Node::Symlink(_) => fuser::FileType::Symlink,
+                    };
+
+                    let full =
+                        reply.add(ino, offset + i as i64 + 1_i64, ty, store_path.to_string());
+                    if full {
+                        break;
+                    }
+                }
+                reply.ok();
+                return;
+            }
         }
 
         // lookup the inode data.
diff --git a/tvix/store/src/fuse/tests.rs b/tvix/store/src/fuse/tests.rs
index e5e36579b6c2..2c99f75471a5 100644
--- a/tvix/store/src/fuse/tests.rs
+++ b/tvix/store/src/fuse/tests.rs
@@ -28,6 +28,17 @@ fn setup_and_mount<P: AsRef<Path>, F>(
 where
     F: Fn(Arc<dyn BlobService>, Arc<dyn DirectoryService>, Arc<dyn PathInfoService>),
 {
+    setup_and_mount_with_listing(mountpoint, setup_fn, false)
+}
+
+fn setup_and_mount_with_listing<P: AsRef<Path>, F>(
+    mountpoint: P,
+    setup_fn: F,
+    list_root: bool,
+) -> Result<fuser::BackgroundSession, std::io::Error>
+where
+    F: Fn(Arc<dyn BlobService>, Arc<dyn DirectoryService>, Arc<dyn PathInfoService>),
+{
     let blob_service = gen_blob_service();
     let directory_service = gen_directory_service();
     let path_info_service = gen_pathinfo_service(blob_service.clone(), directory_service.clone());
@@ -38,7 +49,12 @@ where
         path_info_service.clone(),
     );
 
-    let fs = FUSE::new(blob_service, directory_service, path_info_service);
+    let fs = FUSE::new(
+        blob_service,
+        directory_service,
+        path_info_service,
+        list_root,
+    );
     fuser::spawn_mount2(fs, mountpoint, &[])
 }
 
@@ -280,6 +296,34 @@ fn root() {
     fuser_session.join()
 }
 
+/// Ensure listing the root is allowed if configured explicitly
+#[test]
+fn root_with_listing() {
+    // https://plume.benboeckel.net/~/JustAnotherBlog/skipping-tests-in-rust
+    if !std::path::Path::new("/dev/fuse").exists() {
+        eprintln!("skipping test");
+        return;
+    }
+    let tmpdir = TempDir::new().unwrap();
+
+    let fuser_session =
+        setup_and_mount_with_listing(tmpdir.path(), populate_blob_a, true).expect("must succeed");
+
+    {
+        // read_dir succeeds, but getting the first element will fail.
+        let mut it = fs::read_dir(tmpdir).expect("must succeed");
+
+        let e = it.next().expect("must be some").expect("must succeed");
+
+        let metadata = e.metadata().expect("must succeed");
+        assert!(metadata.is_file());
+        assert!(metadata.permissions().readonly());
+        assert_eq!(fixtures::BLOB_A.len() as u64, metadata.len());
+    }
+
+    fuser_session.join()
+}
+
 /// Ensure we can stat a file at the root
 #[test]
 fn stat_file_at_root() {