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