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| 1 // Copyright (c) 2012 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_POSIX_GLOBAL_DESCRIPTORS_H_ | |
| 6 #define BASE_POSIX_GLOBAL_DESCRIPTORS_H_ | |
| 7 | |
| 8 #include "build/build_config.h" | |
| 9 | |
| 10 #include <vector> | |
| 11 #include <utility> | |
| 12 | |
| 13 #include <stdint.h> | |
| 14 | |
| 15 #include "base/files/memory_mapped_file.h" | |
| 16 #include "base/memory/singleton.h" | |
| 17 | |
| 18 namespace base { | |
| 19 | |
| 20 // It's common practice to install file descriptors into well known slot | |
| 21 // numbers before execing a child; stdin, stdout and stderr are ubiqutous | |
| 22 // examples. | |
| 23 // | |
| 24 // However, when using a zygote model, this becomes troublesome. Since the | |
| 25 // descriptors which need to be in these slots generally aren't known, any code | |
| 26 // could open a resource and take one of the reserved descriptors. Simply | |
| 27 // overwriting the slot isn't a viable solution. | |
| 28 // | |
| 29 // We could try to fill the reserved slots as soon as possible, but this is a | |
| 30 // fragile solution since global constructors etc are able to open files. | |
| 31 // | |
| 32 // Instead, we retreat from the idea of installing descriptors in specific | |
| 33 // slots and add a layer of indirection in the form of this singleton object. | |
| 34 // It maps from an abstract key to a descriptor. If independent modules each | |
| 35 // need to define keys, then values should be chosen randomly so as not to | |
| 36 // collide. | |
| 37 class BASE_EXPORT GlobalDescriptors { | |
| 38 public: | |
| 39 typedef uint32_t Key; | |
| 40 struct Descriptor { | |
| 41 Descriptor(Key key, int fd); | |
| 42 Descriptor(Key key, int fd, base::MemoryMappedFile::Region region); | |
| 43 | |
| 44 // Globally unique key. | |
| 45 Key key; | |
| 46 // Actual FD. | |
| 47 int fd; | |
| 48 // Optional region, defaults to kWholeFile. | |
| 49 base::MemoryMappedFile::Region region; | |
| 50 }; | |
| 51 typedef std::vector<Descriptor> Mapping; | |
| 52 | |
| 53 // Often we want a canonical descriptor for a given Key. In this case, we add | |
| 54 // the following constant to the key value: | |
| 55 #if !defined(OS_ANDROID) | |
| 56 static const int kBaseDescriptor = 3; // 0, 1, 2 are already taken. | |
| 57 #else | |
| 58 static const int kBaseDescriptor = 4; // 3 used by __android_log_write(). | |
| 59 #endif | |
| 60 | |
| 61 // Return the singleton instance of GlobalDescriptors. | |
| 62 static GlobalDescriptors* GetInstance(); | |
| 63 | |
| 64 // Get a descriptor given a key. It is a fatal error if the key is not known. | |
| 65 int Get(Key key) const; | |
| 66 | |
| 67 // Get a descriptor given a key. Returns -1 on error. | |
| 68 int MaybeGet(Key key) const; | |
| 69 | |
| 70 // Get a region given a key. It is a fatal error if the key is not known. | |
| 71 base::MemoryMappedFile::Region GetRegion(Key key) const; | |
| 72 | |
| 73 // Set the descriptor for the given |key|. This sets the region associated | |
| 74 // with |key| to kWholeFile. | |
| 75 void Set(Key key, int fd); | |
| 76 | |
| 77 // Set the descriptor and |region| for the given |key|. | |
| 78 void Set(Key key, int fd, base::MemoryMappedFile::Region region); | |
| 79 | |
| 80 void Reset(const Mapping& mapping); | |
| 81 | |
| 82 private: | |
| 83 friend struct DefaultSingletonTraits<GlobalDescriptors>; | |
| 84 GlobalDescriptors(); | |
| 85 ~GlobalDescriptors(); | |
| 86 | |
| 87 Mapping descriptors_; | |
| 88 }; | |
| 89 | |
| 90 } // namespace base | |
| 91 | |
| 92 #endif // BASE_POSIX_GLOBAL_DESCRIPTORS_H_ | |
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