1 : // Copyright (c) 2009 The Chromium Authors. All rights reserved.
2 : // Use of this source code is governed by a BSD-style license that can be
3 : // found in the LICENSE file.
4 :
5 : #ifndef BASE_FILE_DESCRIPTOR_SHUFFLE_H_
6 : #define BASE_FILE_DESCRIPTOR_SHUFFLE_H_
7 :
8 : // This code exists to perform the shuffling of file descriptors which is
9 : // commonly needed when forking subprocesses. The naive approve is very simple,
10 : // just call dup2 to setup the desired descriptors, but wrong. It's tough to
11 : // handle the edge cases (like mapping 0 -> 1, 1 -> 0) correctly.
12 : //
13 : // In order to unittest this code, it's broken into the abstract action (an
14 : // injective multimap) and the concrete code for dealing with file descriptors.
15 : // Users should use the code like this:
16 : // base::InjectiveMultimap file_descriptor_map;
17 : // file_descriptor_map.push_back(base::InjectionArc(devnull, 0, true));
18 : // file_descriptor_map.push_back(base::InjectionArc(devnull, 2, true));
19 : // file_descriptor_map.push_back(base::InjectionArc(pipe[1], 1, true));
20 : // base::ShuffleFileDescriptors(file_descriptor_map);
21 : //
22 : // and trust the the Right Thing will get done.
23 :
24 : #include <vector>
25 :
26 : namespace base {
27 :
28 : // A Delegate which performs the actions required to perform an injective
29 : // multimapping in place.
30 0 : class InjectionDelegate {
31 : public:
32 : // Duplicate |fd|, an element of the domain, and write a fresh element of the
33 : // domain into |result|. Returns true iff successful.
34 : virtual bool Duplicate(int* result, int fd) = 0;
35 : // Destructively move |src| to |dest|, overwriting |dest|. Returns true iff
36 : // successful.
37 : virtual bool Move(int src, int dest) = 0;
38 : // Delete an element of the domain.
39 : virtual void Close(int fd) = 0;
40 : };
41 :
42 : // An implementation of the InjectionDelegate interface using the file
43 : // descriptor table of the current process as the domain.
44 0 : class FileDescriptorTableInjection : public InjectionDelegate {
45 : bool Duplicate(int* result, int fd);
46 : bool Move(int src, int dest);
47 : void Close(int fd);
48 : };
49 :
50 : // A single arc of the directed graph which describes an injective multimapping.
51 : struct InjectionArc {
52 0 : InjectionArc(int in_source, int in_dest, bool in_close)
53 : : source(in_source),
54 : dest(in_dest),
55 0 : close(in_close) {
56 0 : }
57 :
58 : int source;
59 : int dest;
60 : bool close; // if true, delete the source element after performing the
61 : // mapping.
62 : };
63 :
64 : typedef std::vector<InjectionArc> InjectiveMultimap;
65 :
66 : bool PerformInjectiveMultimap(const InjectiveMultimap& map,
67 : InjectionDelegate* delegate);
68 : bool PerformInjectiveMultimapDestructive(InjectiveMultimap* map,
69 : InjectionDelegate* delegate);
70 :
71 : // This function will not call malloc but will mutate |map|
72 0 : static inline bool ShuffleFileDescriptors(InjectiveMultimap *map) {
73 0 : FileDescriptorTableInjection delegate;
74 0 : return PerformInjectiveMultimapDestructive(map, &delegate);
75 : }
76 :
77 : } // namespace base
78 :
79 : #endif // !BASE_FILE_DESCRIPTOR_SHUFFLE_H_
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