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      1 /*
      2  * Copyright 2012, The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *     http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 #ifndef BCC_SUPPORT_FILE_BASE_H
     18 #define BCC_SUPPORT_FILE_BASE_H
     19 
     20 #include <fcntl.h>
     21 
     22 #include <string>
     23 
     24 #include <llvm/Support/system_error.h>
     25 
     26 namespace android {
     27   class FileMap;
     28 }
     29 
     30 namespace bcc {
     31 
     32 class FileBase {
     33 public:
     34   enum OpenModeEnum {
     35     kReadMode       = 1 << 0,
     36     kWriteMode      = 1 << 1,
     37     kReadWriteMode  = (kReadMode | kWriteMode),
     38   };
     39 
     40   enum FlagEnum {
     41     kBinary = 1 << 0,
     42     kTruncate = 1 << 1,
     43     kAppend = 1 << 2,
     44     kDeleteOnClose = 1 << 3
     45   };
     46 
     47   enum LockModeEnum {
     48     // The shared resource behind the Stream locked in ReadLock mode can be
     49     // locked by other processes at the same time.
     50     kReadLock,
     51 
     52     // The shared resource behind the Stream locked in WriteLock mode can only
     53     // be locked by one process. It's exclusive. That is, the shared resource
     54     // cannot have both ReadLock and WriteLock simultaneously.
     55     kWriteLock
     56   };
     57 
     58   // Default configuration to the lock().
     59   enum {
     60     kDefaultMaxRetryLock = 4,
     61     kDefaultRetryLockInterval = 200000UL,
     62   };
     63 
     64 protected:
     65   // Grant direct access of the internal file descriptor to the sub-class and
     66   // error message such that they can implement their own I/O functionality.
     67   int mFD;
     68 
     69   llvm::error_code mError;
     70 
     71 private:
     72   std::string mName;
     73 
     74   // The 2nd argument to the POSIX open().
     75   unsigned mOpenFlags;
     76 
     77   // True true if we should call unlock() in destructor.
     78   bool mShouldUnlock;
     79 
     80   // True if file should be deleted in destructor.
     81   bool mShouldDelete;
     82 
     83   // Open mName with flag mOpenFlags (using POSIX open().)
     84   bool open();
     85 
     86   // Return true if mFD is the corresponded file descriptor to the file named
     87   // mName on the filesystem. This check may returns failed, for example,
     88   // someone re-create the file with the same name after we openning the file.
     89   bool checkFileIntegrity();
     90 
     91   inline bool reopen() {
     92     // It's a private method, and all its callers are the few that can invoke it.
     93     // That is, the pre-condition will be checked by the caller. Therefore, we don't
     94     // need to check it again in reopen().
     95     close();
     96     return open();
     97   }
     98 
     99 private:
    100   FileBase(FileBase &); // Do not implement.
    101   void operator=(const FileBase &); // Do not implement.
    102 
    103 protected:
    104   // pOpenFlags is the 2nd argument to the POSIX open(). pFlags are the flags to
    105   // FileBase. It's a bit set composed by the value defined in
    106   // FileBase::FlagEnum.
    107   FileBase(const std::string &pFilename, unsigned pOpenFlags, unsigned pFlags);
    108 
    109   void detectError();
    110 
    111 public:
    112   // Lock the file descriptor in given pMode. If pNonblocking is true, the lock
    113   // request issued will return immediately when the shared resource is locked.
    114   // In this case, it retries pMaxRetry times, each wait pRetryInterval (in
    115   // usecs) before the previous retry getting done.
    116   //
    117   // Only file is allowed to use this API.
    118   bool lock(enum LockModeEnum pMode, bool pNonblocking = true,
    119             unsigned pMaxRetry = kDefaultMaxRetryLock,
    120             useconds_t pRetryInterval = kDefaultRetryLockInterval);
    121 
    122   void unlock();
    123 
    124   // Map the file content to the memory.
    125   //
    126   // One who gets non-null android::FileMap returned from this API is responsible
    127   // for destroying it after the use.
    128   android::FileMap *createMap(off_t pOffset, size_t pLength, bool pIsReadOnly);
    129 
    130   size_t getSize();
    131 
    132   off_t seek(off_t pOffset);
    133   off_t tell();
    134 
    135   inline bool hasError() const
    136   { return (mError.value() != llvm::errc::success); }
    137 
    138   inline const llvm::error_code &getError() const
    139   { return mError; }
    140 
    141   // The return value of llvm::error_code::message() is obtained upon the call
    142   // and is passed by value (that is, it's not a member of llvm::error_code.)
    143   inline std::string getErrorMessage() const
    144   { return mError.message(); }
    145 
    146   inline const std::string &getName() const
    147   { return mName; }
    148 
    149   void close();
    150 
    151   virtual ~FileBase();
    152 };
    153 
    154 } // end namespace bcc
    155 
    156 #endif  // BCC_SUPPORT_FILE_BASE_H
    157