1 /*
2  * Copyright (C) 2015 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 #ifndef ANDROID_BASE_UNIQUE_FD_H
18 #define ANDROID_BASE_UNIQUE_FD_H
19 
20 #include <unistd.h>
21 
22 // DO NOT INCLUDE OTHER LIBBASE HEADERS!
23 // This file gets used in libbinder, and libbinder is used everywhere.
24 // Including other headers from libbase frequently results in inclusion of
25 // android-base/macros.h, which causes macro collisions.
26 
27 // Container for a file descriptor that automatically closes the descriptor as
28 // it goes out of scope.
29 //
30 //      unique_fd ufd(open("/some/path", "r"));
31 //      if (ufd.get() == -1) return error;
32 //
33 //      // Do something useful, possibly including 'return'.
34 //
35 //      return 0; // Descriptor is closed for you.
36 //
37 // unique_fd is also known as ScopedFd/ScopedFD/scoped_fd; mentioned here to help
38 // you find this class if you're searching for one of those names.
39 namespace android {
40 namespace base {
41 
42 struct DefaultCloser {
CloseDefaultCloser43   static void Close(int fd) {
44     // Even if close(2) fails with EINTR, the fd will have been closed.
45     // Using TEMP_FAILURE_RETRY will either lead to EBADF or closing someone
46     // else's fd.
47     // http://lkml.indiana.edu/hypermail/linux/kernel/0509.1/0877.html
48     ::close(fd);
49   }
50 };
51 
52 template <typename Closer>
53 class unique_fd_impl final {
54  public:
unique_fd_impl()55   unique_fd_impl() : value_(-1) {}
56 
unique_fd_impl(int value)57   explicit unique_fd_impl(int value) : value_(value) {}
~unique_fd_impl()58   ~unique_fd_impl() { reset(); }
59 
unique_fd_impl(unique_fd_impl && other)60   unique_fd_impl(unique_fd_impl&& other) : value_(other.release()) {}
61   unique_fd_impl& operator=(unique_fd_impl&& s) {
62     reset(s.release());
63     return *this;
64   }
65 
66   void reset(int new_value = -1) {
67     if (value_ != -1) {
68       Closer::Close(value_);
69     }
70     value_ = new_value;
71   }
72 
get()73   int get() const { return value_; }
74   operator int() const { return get(); }
75 
release()76   int release() __attribute__((warn_unused_result)) {
77     int ret = value_;
78     value_ = -1;
79     return ret;
80   }
81 
82  private:
83   int value_;
84 
85   unique_fd_impl(const unique_fd_impl&);
86   void operator=(const unique_fd_impl&);
87 };
88 
89 using unique_fd = unique_fd_impl<DefaultCloser>;
90 
91 }  // namespace base
92 }  // namespace android
93 
94 template <typename T>
95 int close(const android::base::unique_fd_impl<T>&)
96 #if defined(__clang__)
97   __attribute__((__unavailable__(
98 #else
99   __attribute__((__error__(
100 #endif
101     "close called on unique_fd"
102   )));
103 
104 #endif  // ANDROID_BASE_UNIQUE_FD_H
105