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/Optional.h"
13 #include "llvm/ADT/STLExtras.h"
14 #include "llvm/ADT/SmallString.h"
15 #include "llvm/ADT/StringRef.h"
16 #include "llvm/Support/Path.h"
17 #include "llvm/Support/VirtualFileSystem.h"
18 #include <memory>
19 
20 namespace clang {
21 namespace clangd {
22 
23 namespace {
24 /// Always opens files in the underlying filesystem as "volatile", meaning they
25 /// won't be memory-mapped. Memory-mapping isn't desirable for clangd:
26 ///   - edits to the underlying files change contents MemoryBuffers owned by
27 //      SourceManager, breaking its invariants and leading to crashes
28 ///   - it locks files on windows, preventing edits
29 class VolatileFileSystem : public llvm::vfs::ProxyFileSystem {
30 public:
31   explicit VolatileFileSystem(llvm::IntrusiveRefCntPtr<FileSystem> FS)
32       : ProxyFileSystem(std::move(FS)) {}
33 
34   llvm::ErrorOr<std::unique_ptr<llvm::vfs::File>>
35   openFileForRead(const llvm::Twine &InPath) override {
36     llvm::SmallString<128> Path;
37     InPath.toVector(Path);
38 
39     auto File = getUnderlyingFS().openFileForRead(Path);
40     if (!File)
41       return File;
42     // Try to guess preamble files, they can be memory-mapped even on Windows as
43     // clangd has exclusive access to those and nothing else should touch them.
44     llvm::StringRef FileName = llvm::sys::path::filename(Path);
45     if (FileName.startswith("preamble-") && FileName.endswith(".pch"))
46       return File;
47     return std::unique_ptr<VolatileFile>(new VolatileFile(std::move(*File)));
48   }
49 
50 private:
51   class VolatileFile : public llvm::vfs::File {
52   public:
53     VolatileFile(std::unique_ptr<llvm::vfs::File> Wrapped)
54         : Wrapped(std::move(Wrapped)) {
55       assert(this->Wrapped);
56     }
57 
58     virtual llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>>
59     getBuffer(const llvm::Twine &Name, int64_t FileSize,
60               bool RequiresNullTerminator, bool /*IsVolatile*/) override {
61       return Wrapped->getBuffer(Name, FileSize, RequiresNullTerminator,
62                                 /*IsVolatile=*/true);
63     }
64 
65     llvm::ErrorOr<llvm::vfs::Status> status() override {
66       return Wrapped->status();
67     }
68     llvm::ErrorOr<std::string> getName() override { return Wrapped->getName(); }
69     std::error_code close() override { return Wrapped->close(); }
70 
71   private:
72     std::unique_ptr<File> Wrapped;
73   };
74 };
75 } // namespace
76 
77 llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem>
78 ThreadsafeFS::view(PathRef CWD) const {
79   auto FS = view(llvm::None);
80   if (auto EC = FS->setCurrentWorkingDirectory(CWD))
81     elog("VFS: failed to set CWD to {0}: {1}", CWD, EC.message());
82   return FS;
83 }
84 
85 llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem>
86 RealThreadsafeFS::viewImpl() const {
87   // Avoid using memory-mapped files.
88   // FIXME: Try to use a similar approach in Sema instead of relying on
89   //        propagation of the 'isVolatile' flag through all layers.
90   return new VolatileFileSystem(llvm::vfs::createPhysicalFileSystem());
91 }
92 } // namespace clangd
93 } // namespace clang
94