1 //===- FileSystemStatCache.cpp - Caching for 'stat' calls -----------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file defines the FileSystemStatCache interface.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "clang/Basic/FileSystemStatCache.h"
15 #include "llvm/Support/Chrono.h"
16 #include "llvm/Support/ErrorOr.h"
17 #include "llvm/Support/Path.h"
18 #include "llvm/Support/VirtualFileSystem.h"
19 #include <utility>
20
21 using namespace clang;
22
anchor()23 void FileSystemStatCache::anchor() {}
24
copyStatusToFileData(const llvm::vfs::Status & Status,FileData & Data)25 static void copyStatusToFileData(const llvm::vfs::Status &Status,
26 FileData &Data) {
27 Data.Name = Status.getName();
28 Data.Size = Status.getSize();
29 Data.ModTime = llvm::sys::toTimeT(Status.getLastModificationTime());
30 Data.UniqueID = Status.getUniqueID();
31 Data.IsDirectory = Status.isDirectory();
32 Data.IsNamedPipe = Status.getType() == llvm::sys::fs::file_type::fifo_file;
33 Data.InPCH = false;
34 Data.IsVFSMapped = Status.IsVFSMapped;
35 }
36
37 /// FileSystemStatCache::get - Get the 'stat' information for the specified
38 /// path, using the cache to accelerate it if possible. This returns true if
39 /// the path does not exist or false if it exists.
40 ///
41 /// If isFile is true, then this lookup should only return success for files
42 /// (not directories). If it is false this lookup should only return
43 /// success for directories (not files). On a successful file lookup, the
44 /// implementation can optionally fill in FileDescriptor with a valid
45 /// descriptor and the client guarantees that it will close it.
get(StringRef Path,FileData & Data,bool isFile,std::unique_ptr<llvm::vfs::File> * F,FileSystemStatCache * Cache,llvm::vfs::FileSystem & FS)46 bool FileSystemStatCache::get(StringRef Path, FileData &Data, bool isFile,
47 std::unique_ptr<llvm::vfs::File> *F,
48 FileSystemStatCache *Cache,
49 llvm::vfs::FileSystem &FS) {
50 LookupResult R;
51 bool isForDir = !isFile;
52
53 // If we have a cache, use it to resolve the stat query.
54 if (Cache)
55 R = Cache->getStat(Path, Data, isFile, F, FS);
56 else if (isForDir || !F) {
57 // If this is a directory or a file descriptor is not needed and we have
58 // no cache, just go to the file system.
59 llvm::ErrorOr<llvm::vfs::Status> Status = FS.status(Path);
60 if (!Status) {
61 R = CacheMissing;
62 } else {
63 R = CacheExists;
64 copyStatusToFileData(*Status, Data);
65 }
66 } else {
67 // Otherwise, we have to go to the filesystem. We can always just use
68 // 'stat' here, but (for files) the client is asking whether the file exists
69 // because it wants to turn around and *open* it. It is more efficient to
70 // do "open+fstat" on success than it is to do "stat+open".
71 //
72 // Because of this, check to see if the file exists with 'open'. If the
73 // open succeeds, use fstat to get the stat info.
74 auto OwnedFile = FS.openFileForRead(Path);
75
76 if (!OwnedFile) {
77 // If the open fails, our "stat" fails.
78 R = CacheMissing;
79 } else {
80 // Otherwise, the open succeeded. Do an fstat to get the information
81 // about the file. We'll end up returning the open file descriptor to the
82 // client to do what they please with it.
83 llvm::ErrorOr<llvm::vfs::Status> Status = (*OwnedFile)->status();
84 if (Status) {
85 R = CacheExists;
86 copyStatusToFileData(*Status, Data);
87 *F = std::move(*OwnedFile);
88 } else {
89 // fstat rarely fails. If it does, claim the initial open didn't
90 // succeed.
91 R = CacheMissing;
92 *F = nullptr;
93 }
94 }
95 }
96
97 // If the path doesn't exist, return failure.
98 if (R == CacheMissing) return true;
99
100 // If the path exists, make sure that its "directoryness" matches the clients
101 // demands.
102 if (Data.IsDirectory != isForDir) {
103 // If not, close the file if opened.
104 if (F)
105 *F = nullptr;
106
107 return true;
108 }
109
110 return false;
111 }
112
113 MemorizeStatCalls::LookupResult
getStat(StringRef Path,FileData & Data,bool isFile,std::unique_ptr<llvm::vfs::File> * F,llvm::vfs::FileSystem & FS)114 MemorizeStatCalls::getStat(StringRef Path, FileData &Data, bool isFile,
115 std::unique_ptr<llvm::vfs::File> *F,
116 llvm::vfs::FileSystem &FS) {
117 if (get(Path, Data, isFile, F, nullptr, FS)) {
118 // Do not cache failed stats, it is easy to construct common inconsistent
119 // situations if we do, and they are not important for PCH performance
120 // (which currently only needs the stats to construct the initial
121 // FileManager entries).
122 return CacheMissing;
123 }
124
125 // Cache file 'stat' results and directories with absolutely paths.
126 if (!Data.IsDirectory || llvm::sys::path::is_absolute(Path))
127 StatCalls[Path] = Data;
128
129 return CacheExists;
130 }
131