Using fuser to view file usage

 stay android Sometimes we need to check whether a file has been operated by other files through the application , stay linux On the command line, you can use fuser Command view , If the upper class android When the application directly calls the program, it cannot view because of permission （fuser Will pass /proc File system to collect information about related operation files ）, namely fuser Only in root  Only with permission can you give full play to the problem of viewing occupancy . To achieve this goal , Can be fuer Become a running on root On demand service under permission , Through this service, you can indirectly view files . The communication between services and applications can be through property To carry out . As follows ：

 modify init.rc file , Join in fuser service.

service fuser /system/bin/fuser.sh

    user root

    oneshot

    disabled

 increase fuser.sh Run the script as follows ：

#!/system/bin/busybox sh

#app will set boot.CHK_FILE to the file(absolute path) he wants to check,then trigger this service

#the result will be incuded in the proprity ,0 means occupied, 1 means file not exist or some error occuor.

/system/bin/setprop "boot.LOOK_PROG_RES" ""

/system/bin/setprop "boot.LOOK_PROG_STAT" "beginning"

PRG=`/system/bin/getprop "boot.CHK_FILE"`

/system/bin/busybox fuser $PRG

CHK_RESULT=$?

echo check prg=$PRG,result=$CHK_RESULT

/system/bin/setprop "boot.LOOK_PROG_RES" "$CHK_RESULT"

/system/bin/setprop "boot.LOOK_PROG_STAT" "end"

 Embed the following code in the application code ：

SystemProperties.set("boot.CHK_FILE", "/sdcard/music/zh.mp3");

       SystemProperties.set("boot.LOOK_PROG_STAT","");

        SystemService.start("fuser");

        try{Thread.sleep(1000);}catch(Exception e){}

while(SystemProperties.get("boot.LOOK_PROG_STAT").compareTo("end")!=0)

{
   

      Log.v("boot.LOOK_PROG_STAT="+SystemProperties.get("boot.LOOK_PROG_STAT"));

       try{Thread.sleep(100);}catch(Exception e){}

}

Log.v("====get check result:"+SystemProperties.get("boot.LOOK_PROG_RES"));

 Whether to check or not can be realized /sdcard/music/zh.mp3 Whether it is operated by other programs .

 Pay attention to the manifest You need to add system jurisdiction ：

android:sharedUserId="android.uid.system"

 In addition, it needs to be adjusted property_service.c, Add new boot Yes system Authority .