1 //===--- ThreadsafeFS.cpp -------------------------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #include "support/ThreadsafeFS.h"
10 #include "Logger.h"
11 #include "llvm/ADT/None.h"
12 #include "llvm/ADT/SmallString.h"
13 #include "llvm/ADT/StringRef.h"
14 #include "llvm/Support/Path.h"
15 #include "llvm/Support/VirtualFileSystem.h"
16 #include <memory>
17 
18 namespace clang {
19 namespace clangd {
20 
21 namespace {
22 /// Always opens files in the underlying filesystem as "volatile", meaning they
23 /// won't be memory-mapped. Memory-mapping isn't desirable for clangd:
24 ///   - edits to the underlying files change contents MemoryBuffers owned by
25 //      SourceManager, breaking its invariants and leading to crashes
26 ///   - it locks files on windows, preventing edits
27 class VolatileFileSystem : public llvm::vfs::ProxyFileSystem {
28 public:
29   explicit VolatileFileSystem(llvm::IntrusiveRefCntPtr<FileSystem> FS)
30       : ProxyFileSystem(std::move(FS)) {}
31 
32   llvm::ErrorOr<std::unique_ptr<llvm::vfs::File>>
33   openFileForRead(const llvm::Twine &InPath) override {
34     llvm::SmallString<128> Path;
35     InPath.toVector(Path);
36 
37     auto File = getUnderlyingFS().openFileForRead(Path);
38     if (!File)
39       return File;
40     // Try to guess preamble files, they can be memory-mapped even on Windows as
41     // clangd has exclusive access to those and nothing else should touch them.
42     llvm::StringRef FileName = llvm::sys::path::filename(Path);
43     if (FileName.startswith("preamble-") && FileName.endswith(".pch"))
44       return File;
45     return std::unique_ptr<VolatileFile>(new VolatileFile(std::move(*File)));
46   }
47 
48 private:
49   class VolatileFile : public llvm::vfs::File {
50   public:
51     VolatileFile(std::unique_ptr<llvm::vfs::File> Wrapped)
52         : Wrapped(std::move(Wrapped)) {
53       assert(this->Wrapped);
54     }
55 
56     virtual llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>>
57     getBuffer(const llvm::Twine &Name, int64_t FileSize,
58               bool RequiresNullTerminator, bool /*IsVolatile*/) override {
59       return Wrapped->getBuffer(Name, FileSize, RequiresNullTerminator,
60                                 /*IsVolatile=*/true);
61     }
62 
63     llvm::ErrorOr<llvm::vfs::Status> status() override {
64       return Wrapped->status();
65     }
66     llvm::ErrorOr<std::string> getName() override { return Wrapped->getName(); }
67     std::error_code close() override { return Wrapped->close(); }
68 
69   private:
70     std::unique_ptr<File> Wrapped;
71   };
72 };
73 } // namespace
74 
75 llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem>
76 ThreadsafeFS::view(PathRef CWD) const {
77   auto FS = view(llvm::None);
78   if (auto EC = FS->setCurrentWorkingDirectory(CWD))
79     elog("VFS: failed to set CWD to {0}: {1}", CWD, EC.message());
80   return FS;
81 }
82 
83 llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem>
84 RealThreadsafeFS::viewImpl() const {
85   // Avoid using memory-mapped files.
86   // FIXME: Try to use a similar approach in Sema instead of relying on
87   //        propagation of the 'isVolatile' flag through all layers.
88   return new VolatileFileSystem(llvm::vfs::createPhysicalFileSystem());
89 }
90 } // namespace clangd
91 } // namespace clang
92