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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 // FIXME: This is terrible, we need this for ::close.
     19 #if !defined(_MSC_VER) && !defined(__MINGW32__)
     20 #include <unistd.h>
     21 #include <sys/uio.h>
     22 #else
     23 #include <io.h>
     24 #endif
     25 using namespace clang;
     26 
     27 #if defined(_MSC_VER)
     28 #define S_ISDIR(s) ((_S_IFDIR & s) !=0)
     29 #endif
     30 
     31 void FileSystemStatCache::anchor() { }
     32 
     33 static void copyStatusToFileData(const vfs::Status &Status,
     34                                  FileData &Data) {
     35   Data.Name = Status.getName();
     36   Data.Size = Status.getSize();
     37   Data.ModTime = Status.getLastModificationTime().toEpochTime();
     38   Data.UniqueID = Status.getUniqueID();
     39   Data.IsDirectory = Status.isDirectory();
     40   Data.IsNamedPipe = Status.getType() == llvm::sys::fs::file_type::fifo_file;
     41   Data.InPCH = false;
     42   Data.IsVFSMapped = Status.IsVFSMapped;
     43 }
     44 
     45 /// FileSystemStatCache::get - Get the 'stat' information for the specified
     46 /// path, using the cache to accelerate it if possible.  This returns true if
     47 /// the path does not exist or false if it exists.
     48 ///
     49 /// If isFile is true, then this lookup should only return success for files
     50 /// (not directories).  If it is false this lookup should only return
     51 /// success for directories (not files).  On a successful file lookup, the
     52 /// implementation can optionally fill in FileDescriptor with a valid
     53 /// descriptor and the client guarantees that it will close it.
     54 bool FileSystemStatCache::get(const char *Path, FileData &Data, bool isFile,
     55                               std::unique_ptr<vfs::File> *F,
     56                               FileSystemStatCache *Cache, vfs::FileSystem &FS) {
     57   LookupResult R;
     58   bool isForDir = !isFile;
     59 
     60   // If we have a cache, use it to resolve the stat query.
     61   if (Cache)
     62     R = Cache->getStat(Path, Data, isFile, F, FS);
     63   else if (isForDir || !F) {
     64     // If this is a directory or a file descriptor is not needed and we have
     65     // no cache, just go to the file system.
     66     llvm::ErrorOr<vfs::Status> Status = FS.status(Path);
     67     if (!Status) {
     68       R = CacheMissing;
     69     } else {
     70       R = CacheExists;
     71       copyStatusToFileData(*Status, Data);
     72     }
     73   } else {
     74     // Otherwise, we have to go to the filesystem.  We can always just use
     75     // 'stat' here, but (for files) the client is asking whether the file exists
     76     // because it wants to turn around and *open* it.  It is more efficient to
     77     // do "open+fstat" on success than it is to do "stat+open".
     78     //
     79     // Because of this, check to see if the file exists with 'open'.  If the
     80     // open succeeds, use fstat to get the stat info.
     81     std::unique_ptr<vfs::File> OwnedFile;
     82     std::error_code EC = FS.openFileForRead(Path, OwnedFile);
     83 
     84     if (EC) {
     85       // If the open fails, our "stat" fails.
     86       R = CacheMissing;
     87     } else {
     88       // Otherwise, the open succeeded.  Do an fstat to get the information
     89       // about the file.  We'll end up returning the open file descriptor to the
     90       // client to do what they please with it.
     91       llvm::ErrorOr<vfs::Status> Status = OwnedFile->status();
     92       if (Status) {
     93         R = CacheExists;
     94         copyStatusToFileData(*Status, Data);
     95         *F = std::move(OwnedFile);
     96       } else {
     97         // fstat rarely fails.  If it does, claim the initial open didn't
     98         // succeed.
     99         R = CacheMissing;
    100         *F = nullptr;
    101       }
    102     }
    103   }
    104 
    105   // If the path doesn't exist, return failure.
    106   if (R == CacheMissing) return true;
    107 
    108   // If the path exists, make sure that its "directoryness" matches the clients
    109   // demands.
    110   if (Data.IsDirectory != isForDir) {
    111     // If not, close the file if opened.
    112     if (F)
    113       *F = nullptr;
    114 
    115     return true;
    116   }
    117 
    118   return false;
    119 }
    120 
    121 MemorizeStatCalls::LookupResult
    122 MemorizeStatCalls::getStat(const char *Path, FileData &Data, bool isFile,
    123                            std::unique_ptr<vfs::File> *F, vfs::FileSystem &FS) {
    124   LookupResult Result = statChained(Path, Data, isFile, F, FS);
    125 
    126   // Do not cache failed stats, it is easy to construct common inconsistent
    127   // situations if we do, and they are not important for PCH performance (which
    128   // currently only needs the stats to construct the initial FileManager
    129   // entries).
    130   if (Result == CacheMissing)
    131     return Result;
    132 
    133   // Cache file 'stat' results and directories with absolutely paths.
    134   if (!Data.IsDirectory || llvm::sys::path::is_absolute(Path))
    135     StatCalls[Path] = Data;
    136 
    137   return Result;
    138 }
    139