FileMap.h revision edbf3b6af777b721cd2a1ef461947e51e88241e1 
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
29namespace 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 */
45class FileMap {
46public:
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
108protected:
109    // don't delete objects; call release()
110    ~FileMap(void);
111
112private:
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