Android: /cache中的檔案是怎麼消失的

自己放某個檔案到/cache分區，重啟後發現檔案消失了，那麼是怎麼消失的呢?

Step 1. 

packages\providers\DownloadProvider\src\com\android\providers\downloads\StorageManager.java:

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1. /**  
2.  * Removes files in the systemcache and downloads data dir without corresponding entries in  
3.  * the downloads database.  
4.  * This can occur if a delete is done on the database but the file is not removed from the  
5.  * filesystem (due to sudden death of the process, for example).  
6.  * This is not a very common occurrence. So, do this only once in a while.  
7.  */  
8. private void removeSpuriousFiles() {  
9.     if (true || Constants.LOGV) {  
10.         Log.i(Constants.TAG, "in removeSpuriousFiles");  
11.     }  
12.     // get a list of all files in system cache dir and downloads data dir  
13.     List<File> files = new ArrayList<File>();  
14.     File[] listOfFiles = mSystemCacheDir.listFiles();  
15.     if (listOfFiles != null) {  
16.         files.addAll(Arrays.asList(listOfFiles));  
17.     }  
18.     listOfFiles = mDownloadDataDir.listFiles();  
19.     if (listOfFiles != null) {  
20.         files.addAll(Arrays.asList(listOfFiles));  
21.     }  
22.     if (files.size() == 0) {  
23.         return;  
24.     }  
25.     Cursor cursor = mContext.getContentResolver().query(  
26.             Downloads.Impl.ALL_DOWNLOADS_CONTENT_URI,  
27.             new String[] { Downloads.Impl._DATA }, null, null, null);  
28.     try {  
29.         if (cursor != null) {  
30.             while (cursor.moveToNext()) {  
31.                 String filename = cursor.getString(0);  
32.                 if (!TextUtils.isEmpty(filename)) {  
33.                     if (true || Constants.LOGV) {  
34.                         Log.i(Constants.TAG, "in removeSpuriousFiles, preserving file " +  
35.                                 filename);  
36.                     }  
37.                     files.remove(new File(filename));  
38.                 }  
39.             }  
40.         }  
41.     } finally {  
42.         if (cursor != null) {  
43.             cursor.close();  
44.         }  
45.     }  
46.     // delete the files not found in the database  
47.     for (File file : files) {  
48.         if (file.getName().equals(Constants.KNOWN_SPURIOUS_FILENAME) ||  
49.                 file.getName().equalsIgnoreCase(Constants.RECOVERY_DIRECTORY)) {  
50.             continue;  
51.         }  
52.         if (true || Constants.LOGV) {  
53.             Log.i(Constants.TAG, "deleting spurious file " + file.getAbsolutePath());  
54.         }  
55.         file.delete();  
56.     }  
57. }  

    /**     * Removes files in the systemcache and downloads data dir without corresponding entries in     * the downloads database.     * This can occur if a delete is done on the database but the file is not removed from the     * filesystem (due to sudden death of the process, for example).     * This is not a very common occurrence. So, do this only once in a while.     */    private void removeSpuriousFiles() {        if (true || Constants.LOGV) {            Log.i(Constants.TAG, "in removeSpuriousFiles");        }        // get a list of all files in system cache dir and downloads data dir        List<File> files = new ArrayList<File>();        File[] listOfFiles = mSystemCacheDir.listFiles();        if (listOfFiles != null) {            files.addAll(Arrays.asList(listOfFiles));        }        listOfFiles = mDownloadDataDir.listFiles();        if (listOfFiles != null) {            files.addAll(Arrays.asList(listOfFiles));        }        if (files.size() == 0) {            return;        }        Cursor cursor = mContext.getContentResolver().query(                Downloads.Impl.ALL_DOWNLOADS_CONTENT_URI,                new String[] { Downloads.Impl._DATA }, null, null, null);        try {            if (cursor != null) {                while (cursor.moveToNext()) {                    String filename = cursor.getString(0);                    if (!TextUtils.isEmpty(filename)) {                        if (true || Constants.LOGV) {                            Log.i(Constants.TAG, "in removeSpuriousFiles, preserving file " +                                    filename);                        }                        files.remove(new File(filename));                    }                }            }        } finally {            if (cursor != null) {                cursor.close();            }        }        // delete the files not found in the database        for (File file : files) {            if (file.getName().equals(Constants.KNOWN_SPURIOUS_FILENAME) ||                    file.getName().equalsIgnoreCase(Constants.RECOVERY_DIRECTORY)) {                continue;            }            if (true || Constants.LOGV) {                Log.i(Constants.TAG, "deleting spurious file " + file.getAbsolutePath());            }            file.delete();        }    }

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1. /** A magic filename that is allowed to exist within the system cache */  
2. public static final String KNOWN_SPURIOUS_FILENAME = "lost+found";  
3.   
4. /** A magic filename that is allowed to exist within the system cache */  
5. public static final String RECOVERY_DIRECTORY = "recovery";  

    /** A magic filename that is allowed to exist within the system cache */    public static final String KNOWN_SPURIOUS_FILENAME = "lost+found";    /** A magic filename that is allowed to exist within the system cache */    public static final String RECOVERY_DIRECTORY = "recovery";

除 lost+found, recovery這兩個目錄外的檔案都刪掉

Setp 2.

frameworks\base\core\java\android\os\RecoverySystem.java:

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1. /**  
2.  * Called after booting to process and remove recovery-related files.  
3.  * @return the log file from recovery, or null if none was found.  
4.  *  
5.  * @hide  
6.  */  
7. public static String handleAftermath() {  
8.     // Record the tail of the LOG_FILE  
9.     String log = null;  
10.     try {  
11.         log = FileUtils.readTextFile(LOG_FILE, -LOG_FILE_MAX_LENGTH, "...\n");  
12.     } catch (FileNotFoundException e) {  
13.         Log.i(TAG, "No recovery log file");  
14.     } catch (IOException e) {  
15.         Log.e(TAG, "Error reading recovery log", e);  
16.     }  
17.   
18.     // Delete everything in RECOVERY_DIR except those beginning  
19.     // with LAST_PREFIX  
20.     String[] names = RECOVERY_DIR.list();  
21.     for (int i = 0; names != null && i < names.length; i++) {  
22.         if (names[i].startsWith(LAST_PREFIX)) continue;  
23.         File f = new File(RECOVERY_DIR, names[i]);  
24.         if (!f.delete()) {  
25.             Log.e(TAG, "Can't delete: " + f);  
26.         } else {  
27.             Log.i(TAG, "Deleted: " + f);  
28.         }  
29.     }  
30.   
31.     return log;  
32. }  

    /**     * Called after booting to process and remove recovery-related files.     * @return the log file from recovery, or null if none was found.     *     * @hide     */    public static String handleAftermath() {        // Record the tail of the LOG_FILE        String log = null;        try {            log = FileUtils.readTextFile(LOG_FILE, -LOG_FILE_MAX_LENGTH, "...\n");        } catch (FileNotFoundException e) {            Log.i(TAG, "No recovery log file");        } catch (IOException e) {            Log.e(TAG, "Error reading recovery log", e);        }        // Delete everything in RECOVERY_DIR except those beginning        // with LAST_PREFIX        String[] names = RECOVERY_DIR.list();        for (int i = 0; names != null && i < names.length; i++) {            if (names[i].startsWith(LAST_PREFIX)) continue;            File f = new File(RECOVERY_DIR, names[i]);            if (!f.delete()) {                Log.e(TAG, "Can't delete: " + f);            } else {                Log.i(TAG, "Deleted: " + f);            }        }        return log;    }

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1. private static String LAST_PREFIX = "last_";  

private static String LAST_PREFIX = "last_";

/cache/recovery目錄中，除last_開頭的檔案都刪掉

------------------------------------------------

開機走完這兩步後倖存的檔案只有 /cache/lost+found目錄中的檔案，及/cache/recovery/last_ 開頭的檔案了

來自：http://blog.csdn.net/zmyde2010/article/details/7408207