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
anchor()31 void FileSystemStatCache::anchor() { }
32
33 /// FileSystemStatCache::get - Get the 'stat' information for the specified
34 /// path, using the cache to accelerate it if possible. This returns true if
35 /// the path does not exist or false if it exists.
36 ///
37 /// If FileDescriptor is non-null, then this lookup should only return success
38 /// for files (not directories). If it is null this lookup should only return
39 /// success for directories (not files). On a successful file lookup, the
40 /// implementation can optionally fill in FileDescriptor with a valid
41 /// descriptor and the client guarantees that it will close it.
get(const char * Path,struct stat & StatBuf,int * FileDescriptor,FileSystemStatCache * Cache)42 bool FileSystemStatCache::get(const char *Path, struct stat &StatBuf,
43 int *FileDescriptor, FileSystemStatCache *Cache) {
44 LookupResult R;
45 bool isForDir = FileDescriptor == 0;
46
47 // If we have a cache, use it to resolve the stat query.
48 if (Cache)
49 R = Cache->getStat(Path, StatBuf, FileDescriptor);
50 else if (isForDir) {
51 // If this is a directory and we have no cache, just go to the file system.
52 R = ::stat(Path, &StatBuf) != 0 ? CacheMissing : CacheExists;
53 } else {
54 // Otherwise, we have to go to the filesystem. We can always just use
55 // 'stat' here, but (for files) the client is asking whether the file exists
56 // because it wants to turn around and *open* it. It is more efficient to
57 // do "open+fstat" on success than it is to do "stat+open".
58 //
59 // Because of this, check to see if the file exists with 'open'. If the
60 // open succeeds, use fstat to get the stat info.
61 int OpenFlags = O_RDONLY;
62 #ifdef O_BINARY
63 OpenFlags |= O_BINARY; // Open input file in binary mode on win32.
64 #endif
65 *FileDescriptor = ::open(Path, OpenFlags);
66
67 if (*FileDescriptor == -1) {
68 // If the open fails, our "stat" fails.
69 R = CacheMissing;
70 } else {
71 // Otherwise, the open succeeded. Do an fstat to get the information
72 // about the file. We'll end up returning the open file descriptor to the
73 // client to do what they please with it.
74 if (::fstat(*FileDescriptor, &StatBuf) == 0)
75 R = CacheExists;
76 else {
77 // fstat rarely fails. If it does, claim the initial open didn't
78 // succeed.
79 R = CacheMissing;
80 ::close(*FileDescriptor);
81 *FileDescriptor = -1;
82 }
83 }
84 }
85
86 // If the path doesn't exist, return failure.
87 if (R == CacheMissing) return true;
88
89 // If the path exists, make sure that its "directoryness" matches the clients
90 // demands.
91 if (S_ISDIR(StatBuf.st_mode) != isForDir) {
92 // If not, close the file if opened.
93 if (FileDescriptor && *FileDescriptor != -1) {
94 ::close(*FileDescriptor);
95 *FileDescriptor = -1;
96 }
97
98 return true;
99 }
100
101 return false;
102 }
103
104
105 MemorizeStatCalls::LookupResult
getStat(const char * Path,struct stat & StatBuf,int * FileDescriptor)106 MemorizeStatCalls::getStat(const char *Path, struct stat &StatBuf,
107 int *FileDescriptor) {
108 LookupResult Result = statChained(Path, StatBuf, FileDescriptor);
109
110 // Do not cache failed stats, it is easy to construct common inconsistent
111 // situations if we do, and they are not important for PCH performance (which
112 // currently only needs the stats to construct the initial FileManager
113 // entries).
114 if (Result == CacheMissing)
115 return Result;
116
117 // Cache file 'stat' results and directories with absolutely paths.
118 if (!S_ISDIR(StatBuf.st_mode) || llvm::sys::path::is_absolute(Path))
119 StatCalls[Path] = StatBuf;
120
121 return Result;
122 }
123