Android: /cache中的文件是怎么消失的[转]

自己放某个文件到/cache分区，重启后发现文件消失了，那么是怎么消失的呢?

Step 1.

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

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/**
*Removesfilesinthesystemcacheanddownloadsdatadirwithoutcorrespondingentriesin
*thedownloadsdatabase.
*Thiscanoccurifadeleteisdoneonthedatabasebutthefileisnotremovedfromthe
*filesystem(duetosuddendeathoftheprocess,forexample).
*Thisisnotaverycommonoccurrence.So,dothisonlyonceinawhile.
*/
privatevoidremoveSpuriousFiles(){
if(true||Constants.LOGV){
Log.i(Constants.TAG,"inremoveSpuriousFiles");
}
//getalistofallfilesinsystemcachediranddownloadsdatadir
List<File>files=newArrayList<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;
}
Cursorcursor=mContext.getContentResolver().query(
Downloads.Impl.ALL_DOWNLOADS_CONTENT_URI,
newString[]{Downloads.Impl._DATA},null,null,null);
try{
if(cursor!=null){
while(cursor.moveToNext()){
Stringfilename=cursor.getString(0);
if(!TextUtils.isEmpty(filename)){
if(true||Constants.LOGV){
Log.i(Constants.TAG,"inremoveSpuriousFiles,preservingfile"+
filename);
}
files.remove(newFile(filename));
}
}
}
}finally{
if(cursor!=null){
cursor.close();
}
}
//deletethefilesnotfoundinthedatabase
for(Filefile:files){
if(file.getName().equals(Constants.KNOWN_SPURIOUS_FILENAME)||
file.getName().equalsIgnoreCase(Constants.RECOVERY_DIRECTORY)){
continue;
}
if(true||Constants.LOGV){
Log.i(Constants.TAG,"deletingspuriousfile"+file.getAbsolutePath());
}
file.delete();
}
}

    /**     * 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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/**Amagicfilenamethatisallowedtoexistwithinthesystemcache*/
publicstaticfinalStringKNOWN_SPURIOUS_FILENAME="lost+found";
/**Amagicfilenamethatisallowedtoexistwithinthesystemcache*/
publicstaticfinalStringRECOVERY_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这两个目录外的文件都删掉

Setp 2.

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

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/**
*Calledafterbootingtoprocessandremoverecovery-relatedfiles.
*@returnthelogfilefromrecovery,ornullifnonewasfound.
*
*@hide
*/
publicstaticStringhandleAftermath(){
//RecordthetailoftheLOG_FILE
Stringlog=null;
try{
log=FileUtils.readTextFile(LOG_FILE,-LOG_FILE_MAX_LENGTH,"...\n");
}catch(FileNotFoundExceptione){
Log.i(TAG,"Norecoverylogfile");
}catch(IOExceptione){
Log.e(TAG,"Errorreadingrecoverylog",e);
}
//DeleteeverythinginRECOVERY_DIRexceptthosebeginning
//withLAST_PREFIX
String[]names=RECOVERY_DIR.list();
for(inti=0;names!=null&&i<names.length;i++){
if(names[i].startsWith(LAST_PREFIX))continue;
Filef=newFile(RECOVERY_DIR,names[i]);
if(!f.delete()){
Log.e(TAG,"Can'tdelete:"+f);
}else{
Log.i(TAG,"Deleted:"+f);
}
}
returnlog;
}

    /**     * 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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privatestaticStringLAST_PREFIX="last_";

private static String LAST_PREFIX = "last_";

/cache/recovery目录中，除last_开头的文件都删掉

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

开机走完这两步后幸存的文件只有 /cache/lost+found目录中的文件，及/cache/recovery/last_ 开头的文件了

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

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