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      1 /*
      2  * Copyright (C) 2006 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 //
     18 // Encapsulate a shared file mapping.
     19 //
     20 #ifndef __LIBS_FILE_MAP_H
     21 #define __LIBS_FILE_MAP_H
     22 
     23 #include <sys/types.h>
     24 
     25 #ifdef HAVE_WIN32_FILEMAP
     26 #include <windows.h>
     27 #endif
     28 
     29 namespace android {
     30 
     31 /*
     32  * This represents a memory-mapped file.  It might be the entire file or
     33  * only part of it.  This requires a little bookkeeping because the mapping
     34  * needs to be aligned on page boundaries, and in some cases we'd like to
     35  * have multiple references to the mapped area without creating additional
     36  * maps.
     37  *
     38  * This always uses MAP_SHARED.
     39  *
     40  * TODO: we should be able to create a new FileMap that is a subset of
     41  * an existing FileMap and shares the underlying mapped pages.  Requires
     42  * completing the refcounting stuff and possibly introducing the notion
     43  * of a FileMap hierarchy.
     44  */
     45 class FileMap {
     46 public:
     47     FileMap(void);
     48 
     49     /*
     50      * Create a new mapping on an open file.
     51      *
     52      * Closing the file descriptor does not unmap the pages, so we don't
     53      * claim ownership of the fd.
     54      *
     55      * Returns "false" on failure.
     56      */
     57     bool create(const char* origFileName, int fd,
     58                 off_t offset, size_t length, bool readOnly);
     59 
     60     /*
     61      * Return the name of the file this map came from, if known.
     62      */
     63     const char* getFileName(void) const { return mFileName; }
     64 
     65     /*
     66      * Get a pointer to the piece of the file we requested.
     67      */
     68     void* getDataPtr(void) const { return mDataPtr; }
     69 
     70     /*
     71      * Get the length we requested.
     72      */
     73     size_t getDataLength(void) const { return mDataLength; }
     74 
     75     /*
     76      * Get the data offset used to create this map.
     77      */
     78     off_t getDataOffset(void) const { return mDataOffset; }
     79 
     80     /*
     81      * Get a "copy" of the object.
     82      */
     83     FileMap* acquire(void) { mRefCount++; return this; }
     84 
     85     /*
     86      * Call this when mapping is no longer needed.
     87      */
     88     void release(void) {
     89         if (--mRefCount <= 0)
     90             delete this;
     91     }
     92 
     93     /*
     94      * This maps directly to madvise() values, but allows us to avoid
     95      * including <sys/mman.h> everywhere.
     96      */
     97     enum MapAdvice {
     98         NORMAL, RANDOM, SEQUENTIAL, WILLNEED, DONTNEED
     99     };
    100 
    101     /*
    102      * Apply an madvise() call to the entire file.
    103      *
    104      * Returns 0 on success, -1 on failure.
    105      */
    106     int advise(MapAdvice advice);
    107 
    108 protected:
    109     // don't delete objects; call release()
    110     ~FileMap(void);
    111 
    112 private:
    113     // these are not implemented
    114     FileMap(const FileMap& src);
    115     const FileMap& operator=(const FileMap& src);
    116 
    117     int         mRefCount;      // reference count
    118     char*       mFileName;      // original file name, if known
    119     void*       mBasePtr;       // base of mmap area; page aligned
    120     size_t      mBaseLength;    // length, measured from "mBasePtr"
    121     off_t       mDataOffset;    // offset used when map was created
    122     void*       mDataPtr;       // start of requested data, offset from base
    123     size_t      mDataLength;    // length, measured from "mDataPtr"
    124 #ifdef HAVE_WIN32_FILEMAP
    125     HANDLE      mFileHandle;    // Win32 file handle
    126     HANDLE      mFileMapping;   // Win32 file mapping handle
    127 #endif
    128 
    129     static long mPageSize;
    130 };
    131 
    132 }; // namespace android
    133 
    134 #endif // __LIBS_FILE_MAP_H
    135