refactor(tvix/store/fuse): Switch from fuser to fuse-backend-rs r/6621

This switches the FUSE implementation from fuser to fuse-backend-rs.
fuse-backend-rs is designed to work with both FUSE and virtiofs.
Virtiofs support will make it possible to plug the tvix-store into a
microvm and have `/nix/store` access without having to setup FUSE inside
the guest.

Additionally fuse-backend-rs has nice support for running multiple FUSE
threads and has some async support.

The goal of this commit is to mechanically switch over to
fuse-backend-rs with minimal changes. I did have to add some locks here
and there because fuse-backend-rs uses `&self` on all methods whereas
fuser uses `&mut self`. `&self` is required for concurrent access to the
FUSE server, so this makes sense.

We can consider switching to concurrent maps and use some other
techniques to reduce lock contention and critical section size.

Issue: https://b.tvl.fyi/issues/305

Change-Id: Icde5a58c6eef98f8984c1e04e980b756dfb76b47
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9341
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>

1 files changed, 22 insertions, 33 deletions

diff --git a/tvix/store/src/fuse/file_attr.rs b/tvix/store/src/fuse/file_attr.rs
index 25cfd28dd1f9..b946aa977a0a 100644
--- a/tvix/store/src/fuse/file_attr.rs
+++ b/tvix/store/src/fuse/file_attr.rs
@@ -1,20 +1,19 @@
-use std::time::SystemTime;
-
 use super::inodes::{DirectoryInodeData, InodeData};
-use fuser::FileAttr;
+use fuse_backend_rs::abi::fuse_abi::Attr;
 
-/// The [FileAttr] describing the root
-pub const ROOT_FILE_ATTR: FileAttr = FileAttr {
-    ino: fuser::FUSE_ROOT_ID,
+/// 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,
-    atime: SystemTime::UNIX_EPOCH,
-    mtime: SystemTime::UNIX_EPOCH,
-    ctime: SystemTime::UNIX_EPOCH,
-    crtime: SystemTime::UNIX_EPOCH,
-    kind: fuser::FileType::Directory,
-    perm: 0o555,
+    mode: libc::S_IFDIR | 0o555,
+    atime: 0,
+    mtime: 0,
+    ctime: 0,
+    atimensec: 0,
+    mtimensec: 0,
+    ctimensec: 0,
     nlink: 0,
     uid: 0,
     gid: 0,
@@ -22,10 +21,12 @@ pub const ROOT_FILE_ATTR: FileAttr = FileAttr {
     flags: 0,
 };
 
-/// for given &Node and inode, construct a [FileAttr]
-pub fn gen_file_attr(inode_data: &InodeData, inode: u64) -> FileAttr {
-    FileAttr {
+/// 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,
@@ -34,24 +35,12 @@ pub fn gen_file_attr(inode_data: &InodeData, inode: u64) -> FileAttr {
                 children.len() as u64
             }
         },
-        // FUTUREWORK: play with this numbers, as it affects read sizes for client applications.
-        blksize: 1024,
-        blocks: 0,
-        atime: SystemTime::UNIX_EPOCH,
-        mtime: SystemTime::UNIX_EPOCH,
-        ctime: SystemTime::UNIX_EPOCH,
-        crtime: SystemTime::UNIX_EPOCH,
-        kind: inode_data.into(),
-        perm: match inode_data {
-            InodeData::Regular(_, _, false) => 0o444, // no-executable files
-            InodeData::Regular(_, _, true) => 0o555,  // executable files
-            InodeData::Symlink(_) => 0o444,
-            InodeData::Directory(..) => 0o555,
+        mode: match inode_data {
+            InodeData::Regular(_, _, false) => libc::S_IFREG | 0o444, // no-executable files
+            InodeData::Regular(_, _, true) => libc::S_IFREG | 0o555,  // executable files
+            InodeData::Symlink(_) => libc::S_IFLNK | 0o444,
+            InodeData::Directory(_) => libc::S_IFDIR | 0o555,
         },
-        nlink: 0,
-        uid: 0,
-        gid: 0,
-        rdev: 0,
-        flags: 0,
+        ..Default::default()
     }
 }