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 
23 void FileSystemStatCache::anchor() {}
24 
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.
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
114 MemorizeStatCalls::getStat(StringRef Path, FileData &Data, bool isFile,
115                            std::unique_ptr<llvm::vfs::File> *F,
116                            llvm::vfs::FileSystem &FS) {
117   LookupResult Result = statChained(Path, Data, isFile, F, FS);
118 
119   // Do not cache failed stats, it is easy to construct common inconsistent
120   // situations if we do, and they are not important for PCH performance (which
121   // currently only needs the stats to construct the initial FileManager
122   // entries).
123   if (Result == CacheMissing)
124     return Result;
125 
126   // Cache file 'stat' results and directories with absolutely paths.
127   if (!Data.IsDirectory || llvm::sys::path::is_absolute(Path))
128     StatCalls[Path] = Data;
129 
130   return Result;
131 }
132