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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 "llvm/Support/FileSystem.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 llvm::sys::fs::file_status &Status,
     34                                  FileData &Data) {
     35   Data.Size = Status.getSize();
     36   Data.ModTime = Status.getLastModificationTime().toEpochTime();
     37   Data.UniqueID = Status.getUniqueID();
     38   Data.IsDirectory = is_directory(Status);
     39   Data.IsNamedPipe = Status.type() == llvm::sys::fs::file_type::fifo_file;
     40   Data.InPCH = false;
     41 }
     42 
     43 /// FileSystemStatCache::get - Get the 'stat' information for the specified
     44 /// path, using the cache to accelerate it if possible.  This returns true if
     45 /// the path does not exist or false if it exists.
     46 ///
     47 /// If isFile is true, then this lookup should only return success for files
     48 /// (not directories).  If it is false this lookup should only return
     49 /// success for directories (not files).  On a successful file lookup, the
     50 /// implementation can optionally fill in FileDescriptor with a valid
     51 /// descriptor and the client guarantees that it will close it.
     52 bool FileSystemStatCache::get(const char *Path, FileData &Data, bool isFile,
     53                               int *FileDescriptor, FileSystemStatCache *Cache) {
     54   LookupResult R;
     55   bool isForDir = !isFile;
     56 
     57   // If we have a cache, use it to resolve the stat query.
     58   if (Cache)
     59     R = Cache->getStat(Path, Data, isFile, FileDescriptor);
     60   else if (isForDir || !FileDescriptor) {
     61     // If this is a directory or a file descriptor is not needed and we have
     62     // no cache, just go to the file system.
     63     llvm::sys::fs::file_status Status;
     64     if (llvm::sys::fs::status(Path, Status)) {
     65       R = CacheMissing;
     66     } else {
     67       R = CacheExists;
     68       copyStatusToFileData(Status, Data);
     69     }
     70   } else {
     71     // Otherwise, we have to go to the filesystem.  We can always just use
     72     // 'stat' here, but (for files) the client is asking whether the file exists
     73     // because it wants to turn around and *open* it.  It is more efficient to
     74     // do "open+fstat" on success than it is to do "stat+open".
     75     //
     76     // Because of this, check to see if the file exists with 'open'.  If the
     77     // open succeeds, use fstat to get the stat info.
     78     llvm::error_code EC = llvm::sys::fs::openFileForRead(Path, *FileDescriptor);
     79 
     80     if (EC) {
     81       // If the open fails, our "stat" fails.
     82       R = CacheMissing;
     83     } else {
     84       // Otherwise, the open succeeded.  Do an fstat to get the information
     85       // about the file.  We'll end up returning the open file descriptor to the
     86       // client to do what they please with it.
     87       llvm::sys::fs::file_status Status;
     88       if (!llvm::sys::fs::status(*FileDescriptor, Status)) {
     89         R = CacheExists;
     90         copyStatusToFileData(Status, Data);
     91       } else {
     92         // fstat rarely fails.  If it does, claim the initial open didn't
     93         // succeed.
     94         R = CacheMissing;
     95         ::close(*FileDescriptor);
     96         *FileDescriptor = -1;
     97       }
     98     }
     99   }
    100 
    101   // If the path doesn't exist, return failure.
    102   if (R == CacheMissing) return true;
    103 
    104   // If the path exists, make sure that its "directoryness" matches the clients
    105   // demands.
    106   if (Data.IsDirectory != isForDir) {
    107     // If not, close the file if opened.
    108     if (FileDescriptor && *FileDescriptor != -1) {
    109       ::close(*FileDescriptor);
    110       *FileDescriptor = -1;
    111     }
    112 
    113     return true;
    114   }
    115 
    116   return false;
    117 }
    118 
    119 MemorizeStatCalls::LookupResult
    120 MemorizeStatCalls::getStat(const char *Path, FileData &Data, bool isFile,
    121                            int *FileDescriptor) {
    122   LookupResult Result = statChained(Path, Data, isFile, FileDescriptor);
    123 
    124   // Do not cache failed stats, it is easy to construct common inconsistent
    125   // situations if we do, and they are not important for PCH performance (which
    126   // currently only needs the stats to construct the initial FileManager
    127   // entries).
    128   if (Result == CacheMissing)
    129     return Result;
    130 
    131   // Cache file 'stat' results and directories with absolutely paths.
    132   if (!Data.IsDirectory || llvm::sys::path::is_absolute(Path))
    133     StatCalls[Path] = Data;
    134 
    135   return Result;
    136 }
    137