1 //===- FileOutputBuffer.cpp - File Output Buffer ----------------*- C++ -*-===//
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 // Utility for creating a in-memory buffer that will be written to a file.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "llvm/Support/FileOutputBuffer.h"
15 #include "llvm/ADT/STLExtras.h"
16 #include "llvm/ADT/SmallString.h"
17 #include "llvm/Support/Errc.h"
18 #include "llvm/Support/Path.h"
19 #include "llvm/Support/Signals.h"
20 #include <system_error>
21 
22 #if !defined(_MSC_VER) && !defined(__MINGW32__)
23 #include <unistd.h>
24 #else
25 #include <io.h>
26 #endif
27 
28 using llvm::sys::fs::mapped_file_region;
29 
30 namespace llvm {
31 FileOutputBuffer::FileOutputBuffer(std::unique_ptr<mapped_file_region> R,
32                                    StringRef Path, StringRef TmpPath,
33                                    bool IsRegular)
34     : Region(std::move(R)), FinalPath(Path), TempPath(TmpPath),
35       IsRegular(IsRegular) {}
36 
37 FileOutputBuffer::~FileOutputBuffer() {
38   // Close the mapping before deleting the temp file, so that the removal
39   // succeeds.
40   Region.reset();
41   sys::fs::remove(Twine(TempPath));
42 }
43 
44 ErrorOr<std::unique_ptr<FileOutputBuffer>>
45 FileOutputBuffer::create(StringRef FilePath, size_t Size, unsigned Flags) {
46   // Check file is not a regular file, in which case we cannot remove it.
47   sys::fs::file_status Stat;
48   std::error_code EC = sys::fs::status(FilePath, Stat);
49   bool IsRegular = true;
50   switch (Stat.type()) {
51     case sys::fs::file_type::file_not_found:
52       // If file does not exist, we'll create one.
53       break;
54     case sys::fs::file_type::regular_file: {
55         // If file is not currently writable, error out.
56         // FIXME: There is no sys::fs:: api for checking this.
57         // FIXME: In posix, you use the access() call to check this.
58       }
59       break;
60     case sys::fs::file_type::directory_file:
61       return errc::is_a_directory;
62     default:
63       if (EC)
64         return EC;
65       IsRegular = false;
66   }
67 
68   if (IsRegular) {
69     // Delete target file.
70     EC = sys::fs::remove(FilePath);
71     if (EC)
72       return EC;
73   }
74 
75   SmallString<128> TempFilePath;
76   int FD;
77   if (IsRegular) {
78     unsigned Mode = sys::fs::all_read | sys::fs::all_write;
79     // If requested, make the output file executable.
80     if (Flags & F_executable)
81       Mode |= sys::fs::all_exe;
82     // Create new file in same directory but with random name.
83     EC = sys::fs::createUniqueFile(Twine(FilePath) + ".tmp%%%%%%%", FD,
84                                    TempFilePath, Mode);
85   } else {
86     // Create a temporary file. Since this is a special file, we will not move
87     // it and the new file can be in another filesystem. This avoids trying to
88     // create a temporary file in /dev when outputting to /dev/null for example.
89     EC = sys::fs::createTemporaryFile(sys::path::filename(FilePath), "", FD,
90                                       TempFilePath);
91   }
92 
93   if (EC)
94     return EC;
95 
96   sys::RemoveFileOnSignal(TempFilePath);
97 
98 #ifndef LLVM_ON_WIN32
99   // On Windows, CreateFileMapping (the mmap function on Windows)
100   // automatically extends the underlying file. We don't need to
101   // extend the file beforehand. _chsize (ftruncate on Windows) is
102   // pretty slow just like it writes specified amount of bytes,
103   // so we should avoid calling that.
104   EC = sys::fs::resize_file(FD, Size);
105   if (EC)
106     return EC;
107 #endif
108 
109   auto MappedFile = llvm::make_unique<mapped_file_region>(
110       FD, mapped_file_region::readwrite, Size, 0, EC);
111   int Ret = close(FD);
112   if (EC)
113     return EC;
114   if (Ret)
115     return std::error_code(errno, std::generic_category());
116 
117   std::unique_ptr<FileOutputBuffer> Buf(new FileOutputBuffer(
118       std::move(MappedFile), FilePath, TempFilePath, IsRegular));
119   return std::move(Buf);
120 }
121 
122 std::error_code FileOutputBuffer::commit() {
123   // Unmap buffer, letting OS flush dirty pages to file on disk.
124   Region.reset();
125 
126   std::error_code EC;
127   if (IsRegular) {
128     // Rename file to final name.
129     EC = sys::fs::rename(Twine(TempPath), Twine(FinalPath));
130     sys::DontRemoveFileOnSignal(TempPath);
131   } else {
132     EC = sys::fs::copy_file(TempPath, FinalPath);
133     std::error_code RMEC = sys::fs::remove(TempPath);
134     sys::DontRemoveFileOnSignal(TempPath);
135     if (RMEC)
136       return RMEC;
137   }
138 
139   return EC;
140 }
141 } // namespace
142