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/Errc.h"
15 #include "llvm/Support/FileOutputBuffer.h"
16 #include "llvm/ADT/SmallVector.h"
17 #include "llvm/ADT/STLExtras.h"
18 #include "llvm/Support/raw_ostream.h"
19 #include <system_error>
20 
21 using llvm::sys::fs::mapped_file_region;
22 
23 namespace llvm {
24 FileOutputBuffer::FileOutputBuffer(std::unique_ptr<mapped_file_region> R,
25                                    StringRef Path, StringRef TmpPath)
26     : Region(std::move(R)), FinalPath(Path), TempPath(TmpPath) {}
27 
28 FileOutputBuffer::~FileOutputBuffer() {
29   sys::fs::remove(Twine(TempPath));
30 }
31 
32 std::error_code
33 FileOutputBuffer::create(StringRef FilePath, size_t Size,
34                          std::unique_ptr<FileOutputBuffer> &Result,
35                          unsigned Flags) {
36   // If file already exists, it must be a regular file (to be mappable).
37   sys::fs::file_status Stat;
38   std::error_code EC = sys::fs::status(FilePath, Stat);
39   switch (Stat.type()) {
40     case sys::fs::file_type::file_not_found:
41       // If file does not exist, we'll create one.
42       break;
43     case sys::fs::file_type::regular_file: {
44         // If file is not currently writable, error out.
45         // FIXME: There is no sys::fs:: api for checking this.
46         // FIXME: In posix, you use the access() call to check this.
47       }
48       break;
49     default:
50       if (EC)
51         return EC;
52       else
53         return make_error_code(errc::operation_not_permitted);
54   }
55 
56   // Delete target file.
57   EC = sys::fs::remove(FilePath);
58   if (EC)
59     return EC;
60 
61   unsigned Mode = sys::fs::all_read | sys::fs::all_write;
62   // If requested, make the output file executable.
63   if (Flags & F_executable)
64     Mode |= sys::fs::all_exe;
65 
66   // Create new file in same directory but with random name.
67   SmallString<128> TempFilePath;
68   int FD;
69   EC = sys::fs::createUniqueFile(Twine(FilePath) + ".tmp%%%%%%%", FD,
70                                  TempFilePath, Mode);
71   if (EC)
72     return EC;
73 
74   auto MappedFile = llvm::make_unique<mapped_file_region>(
75       FD, true, mapped_file_region::readwrite, Size, 0, EC);
76   if (EC)
77     return EC;
78 
79   Result.reset(
80       new FileOutputBuffer(std::move(MappedFile), FilePath, TempFilePath));
81 
82   return std::error_code();
83 }
84 
85 std::error_code FileOutputBuffer::commit(int64_t NewSmallerSize) {
86   // Unmap buffer, letting OS flush dirty pages to file on disk.
87   Region.reset();
88 
89   // If requested, resize file as part of commit.
90   if ( NewSmallerSize != -1 ) {
91     std::error_code EC = sys::fs::resize_file(Twine(TempPath), NewSmallerSize);
92     if (EC)
93       return EC;
94   }
95 
96   // Rename file to final name.
97   return sys::fs::rename(Twine(TempPath), Twine(FinalPath));
98 }
99 } // namespace
100