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99 lines
3.3 KiB
C++
99 lines
3.3 KiB
C++
// Copyright (c) 2012 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_GLOBAL_DESCRIPTORS_H_
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#define BASE_POSIX_GLOBAL_DESCRIPTORS_H_
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#include "build/build_config.h"
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#include <vector>
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#include <utility>
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#include <stdint.h>
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#include "base/files/memory_mapped_file.h"
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#include "base/files/scoped_file.h"
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#include "base/memory/singleton.h"
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namespace base {
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// It's common practice to install file descriptors into well known slot
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// numbers before execing a child; stdin, stdout and stderr are ubiqutous
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// examples.
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//
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// However, when using a zygote model, this becomes troublesome. Since the
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// descriptors which need to be in these slots generally aren't known, any code
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// could open a resource and take one of the reserved descriptors. Simply
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// overwriting the slot isn't a viable solution.
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//
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// We could try to fill the reserved slots as soon as possible, but this is a
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// fragile solution since global constructors etc are able to open files.
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//
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// Instead, we retreat from the idea of installing descriptors in specific
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// slots and add a layer of indirection in the form of this singleton object.
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// It maps from an abstract key to a descriptor. If independent modules each
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// need to define keys, then values should be chosen randomly so as not to
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// collide.
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//
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// Note that this class is deprecated and passing file descriptor should ideally
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// be done through the command line and using FileDescriptorStore.
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// See https://crbugs.com/detail?id=692619
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class BASE_EXPORT GlobalDescriptors {
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public:
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typedef uint32_t Key;
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struct Descriptor {
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Descriptor(Key key, int fd);
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Descriptor(Key key, int fd, base::MemoryMappedFile::Region region);
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// Globally unique key.
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Key key;
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// Actual FD.
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int fd;
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// Optional region, defaults to kWholeFile.
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base::MemoryMappedFile::Region region;
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};
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typedef std::vector<Descriptor> Mapping;
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// Often we want a canonical descriptor for a given Key. In this case, we add
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// the following constant to the key value:
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static const int kBaseDescriptor = 3; // 0, 1, 2 are already taken.
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// Return the singleton instance of GlobalDescriptors.
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static GlobalDescriptors* GetInstance();
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// Get a descriptor given a key. It is a fatal error if the key is not known.
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int Get(Key key) const;
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// Get a descriptor given a key. Returns -1 on error.
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int MaybeGet(Key key) const;
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// Returns a descriptor given a key and removes it from this class mappings.
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// Also populates |region|.
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// It is a fatal error if the key is not known.
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base::ScopedFD TakeFD(Key key, base::MemoryMappedFile::Region* region);
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// Get a region given a key. It is a fatal error if the key is not known.
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base::MemoryMappedFile::Region GetRegion(Key key) const;
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// Set the descriptor for the given |key|. This sets the region associated
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// with |key| to kWholeFile.
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void Set(Key key, int fd);
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// Set the descriptor and |region| for the given |key|.
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void Set(Key key, int fd, base::MemoryMappedFile::Region region);
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void Reset(const Mapping& mapping);
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private:
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friend struct DefaultSingletonTraits<GlobalDescriptors>;
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GlobalDescriptors();
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~GlobalDescriptors();
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Mapping descriptors_;
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};
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} // namespace base
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#endif // BASE_POSIX_GLOBAL_DESCRIPTORS_H_
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