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// Copyright 2020 Google Inc. // // Licensed under the Apache License, Version 2.0 (the "License"); you may not // use this file except in compliance with the License. You may obtain a copy // of the License at: // // http://www.apache.org/licenses/LICENSE-2.0 // // Unless required by applicable law or agreed to in writing, software // distributed under the License is distributed on an "AS IS" BASIS, WITHOUT // WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the // License for the specific language governing permissions and limitations // under the License. use {fuse, IdGenerator}; use nodes::{ArcNode, Cache, Dir, File, Symlink}; use std::collections::HashMap; use std::fs; use std::path::{Path, PathBuf}; use std::sync::Mutex; /// Node factory without any caching. #[derive(Default)] pub struct NoCache { } impl Cache for NoCache { fn get_or_create(&self, ids: &IdGenerator, underlying_path: &Path, attr: &fs::Metadata, writable: bool) -> ArcNode { if attr.is_dir() { Dir::new_mapped(ids.next(), underlying_path, attr, writable) } else if attr.file_type().is_symlink() { Symlink::new_mapped(ids.next(), underlying_path, attr, writable) } else { File::new_mapped(ids.next(), underlying_path, attr, writable) } } fn delete(&self, _path: &Path, _file_type: fuse::FileType) { // Nothing to do. } fn rename(&self, _old_path: &Path, _new_path: PathBuf, _file_type: fuse::FileType) { // Nothing to do. } } /// Cache of sandboxfs nodes indexed by their underlying path. /// /// This cache is critical to offer good performance during reconfigurations: if the identity of an /// underlying file changes across reconfigurations, the kernel will think it's a different file /// (even if it may not be) and will therefore not be able to take advantage of any caches. You /// would think that avoiding kernel cache invalidations during the reconfiguration itself (e.g. if /// file `A` was mapped and is still mapped now, don't invalidate it) would be sufficient to avoid /// this problem, but it's not: `A` could be mapped, then unmapped, and then remapped again in three /// different reconfigurations, and we'd still not want to lose track of it. /// /// Nodes should be inserted in this cache at creation time and removed from it when explicitly /// deleted by the user (because there is a chance they'll be recreated, and at that point we truly /// want to reload the data from disk). /// /// TODO(jmmv): There currently is no cache expiration, which means that memory usage can grow /// unboundedly. A preliminary attempt at expiring cache entries on a node's forget handler sounded /// promising (because then cache expiration would be delegated to the kernel)... but, on Linux, the /// kernel seems to be calling this very eagerly, rendering our cache useless. I did not track down /// what exactly triggered the forget notifications though. /// /// TODO(jmmv): This cache has proven to be problematic in some cases and should probably be /// removed. See https://jmmv.dev/2020/01/osxfuse-hardlinks-dladdr.html for details. #[derive(Default)] pub struct PathCache { entries: Mutex<HashMap<PathBuf, ArcNode>>, } impl Cache for PathCache { fn get_or_create(&self, ids: &IdGenerator, underlying_path: &Path, attr: &fs::Metadata, writable: bool) -> ArcNode { if attr.is_dir() { // Directories cannot be cached because they contain entries that are created only // in memory based on the mappings configuration. // // TODO(jmmv): Actually, they *could* be cached, but it's hard. Investigate doing so // after quantifying how much it may benefit performance. return Dir::new_mapped(ids.next(), underlying_path, attr, writable); } let mut entries = self.entries.lock().unwrap(); if let Some(node) = entries.get(underlying_path) { if node.writable() == writable { // We have a match from the cache! Return it immediately. // // It is tempting to ensure that the type of the cached node matches the type we // want to return based on the metadata we have now in `attr`... but doing so does // not really prevent problems: the type of the underlying file can change at any // point in time. We could check this here and the type could change immediately // afterwards behind our backs, so don't bother. return node.clone(); } // We had a match... but node writability has changed; recreate the node. // // You may wonder why we care about this and not the file type as described above: the // reason is that the writability property is a setting of the mappings, not a property // of the underlying files, and thus it's a setting that we fully control and must keep // correct across reconfigurations or across different mappings of the same files. info!("Missed node caching opportunity because writability has changed for {:?}", underlying_path) } let node: ArcNode = if attr.is_dir() { panic!("Directory entries cannot be cached and are handled above"); } else if attr.file_type().is_symlink() { Symlink::new_mapped(ids.next(), underlying_path, attr, writable) } else { File::new_mapped(ids.next(), underlying_path, attr, writable) }; entries.insert(underlying_path.to_path_buf(), node.clone()); node } fn delete(&self, path: &Path, file_type: fuse::FileType) { let mut entries = self.entries.lock().unwrap(); if file_type == fuse::FileType::Directory { debug_assert!(!entries.contains_key(path), "Directories are not currently cached"); } else { entries.remove(path).expect("Tried to delete unknown path from the cache"); } } fn rename(&self, old_path: &Path, new_path: PathBuf, file_type: fuse::FileType) { let mut entries = self.entries.lock().unwrap(); if file_type == fuse::FileType::Directory { debug_assert!(!entries.contains_key(old_path), "Directories are not currently cached"); } else { let node = entries.remove(old_path).expect("Tried to rename unknown path in the cache"); entries.insert(new_path, node); } } } #[cfg(test)] mod tests { use super::*; use tempfile::tempdir; use testutils; #[test] fn path_cache_behavior() { let root = tempdir().unwrap(); let dir1 = root.path().join("dir1"); fs::create_dir(&dir1).unwrap(); let dir1attr = fs::symlink_metadata(&dir1).unwrap(); let file1 = root.path().join("file1"); drop(fs::File::create(&file1).unwrap()); let file1attr = fs::symlink_metadata(&file1).unwrap(); let file2 = root.path().join("file2"); drop(fs::File::create(&file2).unwrap()); let file2attr = fs::symlink_metadata(&file2).unwrap(); let ids = IdGenerator::new(1); let cache = PathCache::default(); // Directories are not cached no matter what. assert_eq!(1, cache.get_or_create(&ids, &dir1, &dir1attr, false).inode()); assert_eq!(2, cache.get_or_create(&ids, &dir1, &dir1attr, false).inode()); assert_eq!(3, cache.get_or_create(&ids, &dir1, &dir1attr, true).inode()); // Different files get different nodes. assert_eq!(4, cache.get_or_create(&ids, &file1, &file1attr, false).inode()); assert_eq!(5, cache.get_or_create(&ids, &file2, &file2attr, true).inode()); // Files we queried before but with different writability get different nodes. assert_eq!(6, cache.get_or_create(&ids, &file1, &file1attr, true).inode()); assert_eq!(7, cache.get_or_create(&ids, &file2, &file2attr, false).inode()); // We get cache hits when everything matches previous queries. assert_eq!(6, cache.get_or_create(&ids, &file1, &file1attr, true).inode()); assert_eq!(7, cache.get_or_create(&ids, &file2, &file2attr, false).inode()); // We don't get cache hits for nodes whose writability changed. assert_eq!(8, cache.get_or_create(&ids, &file1, &file1attr, false).inode()); assert_eq!(9, cache.get_or_create(&ids, &file2, &file2attr, true).inode()); } #[test] fn path_cache_nodes_support_all_file_types() { let ids = IdGenerator::new(1); let cache = PathCache::default(); for (_fuse_type, path) in testutils::AllFileTypes::new().entries { let fs_attr = fs::symlink_metadata(&path).unwrap(); // The following panics if it's impossible to represent the given file type, which is // what we are testing. cache.get_or_create(&ids, &path, &fs_attr, false); } } }