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/Path.h"
16 #include <fcntl.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 /// FileSystemStatCache::get - Get the 'stat' information for the specified
32 /// path, using the cache to accelerate it if possible.  This returns true if
33 /// the path does not exist or false if it exists.
34 ///
35 /// If FileDescriptor is non-null, then this lookup should only return success
36 /// for files (not directories).  If it is null this lookup should only return
37 /// success for directories (not files).  On a successful file lookup, the
38 /// implementation can optionally fill in FileDescriptor with a valid
39 /// descriptor and the client guarantees that it will close it.
40 bool FileSystemStatCache::get(const char *Path, struct stat &StatBuf,
41                               int *FileDescriptor, FileSystemStatCache *Cache) {
42   LookupResult R;
43   bool isForDir = FileDescriptor == 0;
44 
45   // If we have a cache, use it to resolve the stat query.
46   if (Cache)
47     R = Cache->getStat(Path, StatBuf, FileDescriptor);
48   else if (isForDir) {
49     // If this is a directory and we have no cache, just go to the file system.
50     R = ::stat(Path, &StatBuf) != 0 ? CacheMissing : CacheExists;
51   } else {
52     // Otherwise, we have to go to the filesystem.  We can always just use
53     // 'stat' here, but (for files) the client is asking whether the file exists
54     // because it wants to turn around and *open* it.  It is more efficient to
55     // do "open+fstat" on success than it is to do "stat+open".
56     //
57     // Because of this, check to see if the file exists with 'open'.  If the
58     // open succeeds, use fstat to get the stat info.
59     int OpenFlags = O_RDONLY;
60 #ifdef O_BINARY
61     OpenFlags |= O_BINARY;  // Open input file in binary mode on win32.
62 #endif
63     *FileDescriptor = ::open(Path, OpenFlags);
64 
65     if (*FileDescriptor == -1) {
66       // If the open fails, our "stat" fails.
67       R = CacheMissing;
68     } else {
69       // Otherwise, the open succeeded.  Do an fstat to get the information
70       // about the file.  We'll end up returning the open file descriptor to the
71       // client to do what they please with it.
72       if (::fstat(*FileDescriptor, &StatBuf) == 0)
73         R = CacheExists;
74       else {
75         // fstat rarely fails.  If it does, claim the initial open didn't
76         // succeed.
77         R = CacheMissing;
78         ::close(*FileDescriptor);
79         *FileDescriptor = -1;
80       }
81     }
82   }
83 
84   // If the path doesn't exist, return failure.
85   if (R == CacheMissing) return true;
86 
87   // If the path exists, make sure that its "directoryness" matches the clients
88   // demands.
89   if (S_ISDIR(StatBuf.st_mode) != isForDir) {
90     // If not, close the file if opened.
91     if (FileDescriptor && *FileDescriptor != -1) {
92       ::close(*FileDescriptor);
93       *FileDescriptor = -1;
94     }
95 
96     return true;
97   }
98 
99   return false;
100 }
101 
102 
103 MemorizeStatCalls::LookupResult
104 MemorizeStatCalls::getStat(const char *Path, struct stat &StatBuf,
105                            int *FileDescriptor) {
106   LookupResult Result = statChained(Path, StatBuf, FileDescriptor);
107 
108   // Do not cache failed stats, it is easy to construct common inconsistent
109   // situations if we do, and they are not important for PCH performance (which
110   // currently only needs the stats to construct the initial FileManager
111   // entries).
112   if (Result == CacheMissing)
113     return Result;
114 
115   // Cache file 'stat' results and directories with absolutely paths.
116   if (!S_ISDIR(StatBuf.st_mode) || llvm::sys::path::is_absolute(Path))
117     StatCalls[Path] = StatBuf;
118 
119   return Result;
120 }
121