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83 lines
3.0 KiB
C++
83 lines
3.0 KiB
C++
// Copyright (c) 2011 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef BASE_POSIX_FILE_DESCRIPTOR_SHUFFLE_H_
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#define BASE_POSIX_FILE_DESCRIPTOR_SHUFFLE_H_
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// This code exists to shuffle file descriptors, which is commonly needed when
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// forking subprocesses. The naive approach (just call dup2 to set up the
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// desired descriptors) is very simple, but wrong: it won't handle edge cases
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// (like mapping 0 -> 1, 1 -> 0) correctly.
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//
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// In order to unittest this code, it's broken into the abstract action (an
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// injective multimap) and the concrete code for dealing with file descriptors.
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// Users should use the code like this:
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// base::InjectiveMultimap file_descriptor_map;
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// file_descriptor_map.push_back(base::InjectionArc(devnull, 0, true));
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// file_descriptor_map.push_back(base::InjectionArc(devnull, 2, true));
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// file_descriptor_map.push_back(base::InjectionArc(pipe[1], 1, true));
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// base::ShuffleFileDescriptors(file_descriptor_map);
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//
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// and trust the the Right Thing will get done.
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#include <vector>
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#include "base/compiler_specific.h"
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namespace base {
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// A Delegate which performs the actions required to perform an injective
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// multimapping in place.
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class InjectionDelegate {
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public:
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// Duplicate |fd|, an element of the domain, and write a fresh element of the
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// domain into |result|. Returns true iff successful.
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virtual bool Duplicate(int* result, int fd) = 0;
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// Destructively move |src| to |dest|, overwriting |dest|. Returns true iff
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// successful.
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virtual bool Move(int src, int dest) = 0;
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// Delete an element of the domain.
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virtual void Close(int fd) = 0;
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protected:
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virtual ~InjectionDelegate() = default;
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};
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// An implementation of the InjectionDelegate interface using the file
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// descriptor table of the current process as the domain.
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class FileDescriptorTableInjection : public InjectionDelegate {
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bool Duplicate(int* result, int fd) override;
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bool Move(int src, int dest) override;
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void Close(int fd) override;
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};
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// A single arc of the directed graph which describes an injective multimapping.
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struct InjectionArc {
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InjectionArc(int in_source, int in_dest, bool in_close)
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: source(in_source), dest(in_dest), close(in_close) {}
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int source;
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int dest;
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bool close; // if true, delete the source element after performing the
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// mapping.
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};
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typedef std::vector<InjectionArc> InjectiveMultimap;
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bool PerformInjectiveMultimap(const InjectiveMultimap& map,
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InjectionDelegate* delegate);
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bool PerformInjectiveMultimapDestructive(InjectiveMultimap* map,
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InjectionDelegate* delegate);
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// This function will not call malloc but will mutate |map|
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static inline bool ShuffleFileDescriptors(InjectiveMultimap* map) {
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FileDescriptorTableInjection delegate;
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return PerformInjectiveMultimapDestructive(map, &delegate);
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}
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} // namespace base
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#endif // BASE_POSIX_FILE_DESCRIPTOR_SHUFFLE_H_
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