refactor(tvix/castore/fs): remove From<Node> for InodeData r/7931

These were copying unnecessarily. Instead, have a
InodeData::from_node(), which *consumes* the Node entirely, returns
`InodeData` and the split-off name (which is not part of InodeData).

Callers can then use the result in various helper functions, like:

 - InodeData::as_fuse_type
 - InodeData::as_fuse_file_attr
 - InodeData::as_fuse_entry

… to prepare their replies to the kernel.

This removes not only a bunch of clones, but also a lot of copy-pasted
code.

Change-Id: Idbca5f25cc29e96c1f4c614b33dff2becb0a8738
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11435
Tested-by: BuildkiteCI
Autosubmit: flokli <flokli@flokli.de>
Reviewed-by: Connor Brewster <cbrewster@hey.com>

2 files changed, 76 insertions, 107 deletions

diff --git a/tvix/castore/src/fs/inodes.rs b/tvix/castore/src/fs/inodes.rs
index 69a75acb6b0d..c22bd4b2ebdc 100644
--- a/tvix/castore/src/fs/inodes.rs
+++ b/tvix/castore/src/fs/inodes.rs
@@ -2,6 +2,8 @@
 //! about inodes, which present tvix-castore nodes in a filesystem.
 use std::time::Duration;
 
+use bytes::Bytes;
+
 use crate::proto as castorepb;
 use crate::B3Digest;
 
@@ -12,7 +14,36 @@ pub enum InodeData {
     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 InodeData {
+    /// Constructs a new InodeData by consuming a [Node].
+    /// It splits off the orginal name, so it can be used later.
+    pub fn from_node(node: castorepb::node::Node) -> (Self, Bytes) {
+        match node {
+            castorepb::node::Node::Directory(n) => (
+                Self::Directory(DirectoryInodeData::Sparse(
+                    n.digest.try_into().unwrap(),
+                    n.size,
+                )),
+                n.name,
+            ),
+            castorepb::node::Node::File(n) => (
+                Self::Regular(n.digest.try_into().unwrap(), n.size, n.executable),
+                n.name,
+            ),
+            castorepb::node::Node::Symlink(n) => (Self::Symlink(n.target), n.name),
+        }
+    }
+
     pub fn as_fuse_file_attr(&self, inode: u64) -> fuse_backend_rs::abi::fuse_abi::Attr {
         fuse_backend_rs::abi::fuse_abi::Attr {
             ino: inode,
@@ -45,50 +76,19 @@ impl InodeData {
             ..Default::default()
         }
     }
-}
-
-/// 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,
-        )
-    }
-}
+    /// Returns the u32 fuse type
+    pub fn as_fuse_type(&self) -> u32 {
+        #[allow(clippy::let_and_return)]
+        let ty = match self {
+            InodeData::Regular(_, _, _) => libc::S_IFREG,
+            InodeData::Symlink(_) => libc::S_IFLNK,
+            InodeData::Directory(_) => libc::S_IFDIR,
+        };
+        // libc::S_IFDIR is u32 on Linux and u16 on MacOS
+        #[cfg(target_os = "macos")]
+        let ty = ty as u32;
 
-/// 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,
-        ))
+        ty
     }
 }
diff --git a/tvix/castore/src/fs/mod.rs b/tvix/castore/src/fs/mod.rs
index 1988a49cfc15..b714bad1e868 100644
--- a/tvix/castore/src/fs/mod.rs
+++ b/tvix/castore/src/fs/mod.rs
@@ -26,6 +26,7 @@ use crate::{
     B3Digest,
 };
 use bstr::ByteVec;
+use bytes::Bytes;
 use fuse_backend_rs::abi::fuse_abi::{stat64, OpenOptions};
 use fuse_backend_rs::api::filesystem::{
     Context, FileSystem, FsOptions, GetxattrReply, ListxattrReply, ROOT_ID,
@@ -91,7 +92,7 @@ pub struct TvixStoreFs<BS, DS, RN> {
     show_xattr: bool,
 
     /// This maps a given basename in the root to the inode we allocated for the node.
-    root_nodes: RwLock<HashMap<Vec<u8>, u64>>,
+    root_nodes: RwLock<HashMap<Bytes, u64>>,
 
     /// This keeps track of inodes and data alongside them.
     inode_tracker: RwLock<InodeTracker>,
@@ -196,13 +197,16 @@ where
 
                 // Turn the retrieved directory into a InodeData::Directory(DirectoryInodeData::Populated(..)),
                 // allocating inodes for the children on the way.
+                // FUTUREWORK: there's a bunch of cloning going on here, which we can probably avoid.
                 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());
+                            let (inode_data, _) = InodeData::from_node(child_node.clone());
+
+                            let child_ino = inode_tracker.put(inode_data);
                             (child_ino, child_node)
                         })
                         .collect();
@@ -263,7 +267,7 @@ where
             // 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(ref root_node)) => {
+            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");
@@ -286,9 +290,9 @@ where
 
                 // insert the (sparse) inode data and register in
                 // self.root_nodes.
-                let inode_data: InodeData = root_node.into();
+                let (inode_data, name) = InodeData::from_node(root_node);
                 let ino = inode_tracker.put(inode_data.clone());
-                root_nodes.insert(name.to_bytes().into(), ino);
+                root_nodes.insert(name, ino);
 
                 Ok((ino, Arc::new(inode_data)))
             }
@@ -463,30 +467,22 @@ where
                     io::Error::from_raw_os_error(libc::EIO)
                 })?;
 
-                let name = root_node.get_name();
-                let ty = match root_node {
-                    Node::Directory(_) => libc::S_IFDIR,
-                    Node::File(_) => libc::S_IFREG,
-                    Node::Symlink(_) => libc::S_IFLNK,
-                };
+                let (inode_data, name) = InodeData::from_node(root_node);
 
                 // obtain the inode, or allocate a new one.
-                let ino = self.get_inode_for_root_name(name).unwrap_or_else(|| {
+                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);
+                    let ino = self.inode_tracker.write().put(inode_data.clone());
+                    self.root_nodes.write().insert(name.clone(), ino);
                     ino
                 });
 
-                #[cfg(target_os = "macos")]
-                let ty = ty as u32;
-
                 let written = add_entry(fuse_backend_rs::api::filesystem::DirEntry {
                     ino,
                     offset: offset + i as u64 + 1,
-                    type_: ty,
-                    name,
+                    type_: inode_data.as_fuse_type(),
+                    name: &name,
                 })?;
                 // If the buffer is full, add_entry will return `Ok(0)`.
                 if written == 0 {
@@ -500,23 +496,15 @@ where
         let (parent_digest, children) = self.get_directory_children(inode)?;
         Span::current().record("directory.digest", parent_digest.to_string());
 
-        for (i, (ino, child_node)) in children.iter().skip(offset as usize).enumerate() {
+        for (i, (ino, child_node)) in children.into_iter().skip(offset as usize).enumerate() {
+            let (inode_data, name) = InodeData::from_node(child_node);
+
             // the second parameter will become the "offset" parameter on the next call.
             let written = add_entry(fuse_backend_rs::api::filesystem::DirEntry {
-                ino: *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(),
+                type_: inode_data.as_fuse_type(),
+                name: &name,
             })?;
             // If the buffer is full, add_entry will return `Ok(0)`.
             if written == 0 {
@@ -566,33 +554,23 @@ where
                     io::Error::from_raw_os_error(libc::EPERM)
                 })?;
 
-                let name = root_node.get_name();
-                let ty = match root_node {
-                    Node::Directory(_) => libc::S_IFDIR,
-                    Node::File(_) => libc::S_IFREG,
-                    Node::Symlink(_) => libc::S_IFLNK,
-                };
-
-                let inode_data: InodeData = (&root_node).into();
+                let (inode_data, name) = InodeData::from_node(root_node);
 
                 // obtain the inode, or allocate a new one.
-                let ino = self.get_inode_for_root_name(name).unwrap_or_else(|| {
+                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(inode_data.clone());
-                    self.root_nodes.write().insert(name.into(), ino);
+                    self.root_nodes.write().insert(name.clone(), ino);
                     ino
                 });
 
-                #[cfg(target_os = "macos")]
-                let ty = ty as u32;
-
                 let written = add_entry(
                     fuse_backend_rs::api::filesystem::DirEntry {
                         ino,
                         offset: offset + i as u64 + 1,
-                        type_: ty,
-                        name,
+                        type_: inode_data.as_fuse_type(),
+                        name: &name,
                     },
                     inode_data.as_fuse_entry(ino),
                 )?;
@@ -608,27 +586,18 @@ where
         let (parent_digest, children) = self.get_directory_children(inode)?;
         Span::current().record("directory.digest", parent_digest.to_string());
 
-        for (i, (ino, child_node)) in children.iter().skip(offset as usize).enumerate() {
-            let inode_data: InodeData = child_node.into();
+        for (i, (ino, child_node)) in children.into_iter().skip(offset as usize).enumerate() {
+            let (inode_data, name) = InodeData::from_node(child_node);
+
             // the second parameter will become the "offset" parameter on the next call.
             let written = add_entry(
                 fuse_backend_rs::api::filesystem::DirEntry {
-                    ino: *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(),
+                    type_: inode_data.as_fuse_type(),
+                    name: &name,
                 },
-                inode_data.as_fuse_entry(*ino),
+                inode_data.as_fuse_entry(ino),
             )?;
             // If the buffer is full, add_entry will return `Ok(0)`.
             if written == 0 {