1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
|
// Copyright (c) 2009 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_FILE_DESCRIPTOR_SHUFFLE_H_
#define BASE_FILE_DESCRIPTOR_SHUFFLE_H_
#pragma once
// This code exists to perform the shuffling of file descriptors which is
// commonly needed when forking subprocesses. The naive approve is very simple,
// just call dup2 to setup the desired descriptors, but wrong. It's tough to
// handle the edge cases (like mapping 0 -> 1, 1 -> 0) correctly.
//
// In order to unittest this code, it's broken into the abstract action (an
// injective multimap) and the concrete code for dealing with file descriptors.
// Users should use the code like this:
// base::InjectiveMultimap file_descriptor_map;
// file_descriptor_map.push_back(base::InjectionArc(devnull, 0, true));
// file_descriptor_map.push_back(base::InjectionArc(devnull, 2, true));
// file_descriptor_map.push_back(base::InjectionArc(pipe[1], 1, true));
// base::ShuffleFileDescriptors(file_descriptor_map);
//
// and trust the the Right Thing will get done.
#include <vector>
namespace base {
// A Delegate which performs the actions required to perform an injective
// multimapping in place.
class InjectionDelegate {
public:
// Duplicate |fd|, an element of the domain, and write a fresh element of the
// domain into |result|. Returns true iff successful.
virtual bool Duplicate(int* result, int fd) = 0;
// Destructively move |src| to |dest|, overwriting |dest|. Returns true iff
// successful.
virtual bool Move(int src, int dest) = 0;
// Delete an element of the domain.
virtual void Close(int fd) = 0;
protected:
virtual ~InjectionDelegate() {}
};
// An implementation of the InjectionDelegate interface using the file
// descriptor table of the current process as the domain.
class FileDescriptorTableInjection : public InjectionDelegate {
virtual bool Duplicate(int* result, int fd);
virtual bool Move(int src, int dest);
virtual void Close(int fd);
};
// A single arc of the directed graph which describes an injective multimapping.
struct InjectionArc {
InjectionArc(int in_source, int in_dest, bool in_close)
: source(in_source),
dest(in_dest),
close(in_close) {
}
int source;
int dest;
bool close; // if true, delete the source element after performing the
// mapping.
};
typedef std::vector<InjectionArc> InjectiveMultimap;
bool PerformInjectiveMultimap(const InjectiveMultimap& map,
InjectionDelegate* delegate);
bool PerformInjectiveMultimapDestructive(InjectiveMultimap* map,
InjectionDelegate* delegate);
// This function will not call malloc but will mutate |map|
static inline bool ShuffleFileDescriptors(InjectiveMultimap* map) {
FileDescriptorTableInjection delegate;
return PerformInjectiveMultimapDestructive(map, &delegate);
}
} // namespace base
#endif // BASE_FILE_DESCRIPTOR_SHUFFLE_H_
|
