Operating Systems I
Homework II
Readme
1st October 2012

About
============================
We added a new system call to Android Linux
Kernel. This system call is called ptree and it returns
into the given buffer a depth first pre-order list of 
processes running on the system. The return value of the system call
is total actual number of process running. 


Code Changed
==============

The main relevant files added are: 

include/linux/prinfo.h -> Includes a structure that defines the information about a process that is returned.
This structure is defined as follows:
struct prinfo {
	long state;			/* current state of process */
	pid_t pid;			/* process id */
	pid_t parent_pid;		/* process id of parent */
	pid_t first_child_pid;  	/* pid of youngest child */
	pid_t next_sibling_pid;  	/* pid of older sibling */
	long uid;			/* user id of process owner */
	char comm[64];			/* name of program executed */
};

kernel/ptree.c ->  System call implementation
kernel/ptree.h -> Header file


How to Compile Kernel
=====================
The first time you type: 
Change directory to the kernel root folder. Then execute: 

make ARCH=arm goldfish_armv7_defconfig 
make ARCH=arm CROSS_COMPILE=arm-none-linux-gnueabi-


On Subsequent recompiles, it is easier to make a short cut by doing:
alias armmake="make -j2 ARCH=arm CROSS_COMPILE=arm-none-linux-gnueabi-"

Then you can run the re-compile by just doing: "armmake"


How to Compile Test Program
===========================

Change directory into the 'test-program' folder. Then execute:
make


How to Run Test Program
==================
I'm assuming you have Android SDK tools in your Path. 
1) Compile Test Program
2) Compile Kernel
3) Start an Android emulator with the modified kernel image by doing: 
emulator -avd OS_W41118 -kernel arch\arm\boot\zImage -show-kernel -no-snapshot-load

4) Push the new binary to the Running Emulator: 
adb push test-program\ptree_test /data/misc

5) Open a shell into the emulator:
adb shell

6) Execute the test program
/data/misc/ptree_test

NB: If you get an execution error and you're on Windows, then run this command first. 
cd /data/misc
chmod 751 *

Then try running the test program again. 

Error Handling
=================
We did our best to handle error conditions gracefully in both the kernel code and the test user program. 


Testing
=================
We tested our system call by running the test-program on the emulator. An example output of the test
output is given below: 

./ptree_test 5
 init,1,1,0,29,2,0
         ueventd,29,1,1,0,30,0
         servicemanager,30,1,1,0,31,1000
         vold,31,1,1,0,33,0
         netd,33,1,1,0,34,0

You will notice that the ptree_test program takes in an optional parameter that determines how many processes should
be returned. (This is the nr value)

Running ptree_test with no arguments defaults the number to 100. You should an output like this:

# ./ptree_test
./ptree_test
 init,1,1,0,29,2,0
         ueventd,29,1,1,0,30,0
         servicemanager,30,1,1,0,31,1000
         vold,31,1,1,0,33,0
         netd,33,1,1,0,34,0
         debuggerd,34,1,1,0,35,0
         rild,35,1,1,0,36,1001
         surfaceflinger,36,1,1,0,37,1000
         zygote,37,1,1,148,38,0
                 system_server,148,1,37,0,149,1000
                 ndroid.systemui,203,1,37,0,207,10022
                 m.android.phone,233,1,37,0,234,1001
                 ndroid.launcher,246,1,37,0,248,10009
                 ndroid.settings,270,1,37,0,273,1000
                 ndroid.contacts,297,1,37,0,299,10001
                 d.process.acore,318,1,37,0,320,10001
                 com.android.mms,353,1,37,0,356,10002
                 d.process.media,369,1,37,0,371,10010
                 putmethod.latin,386,1,37,0,389,10000
                 m.android.email,415,1,37,0,417,10005
                 ndroid.exchange,432,1,37,0,434,10031
                 droid.deskclock,451,1,37,0,454,10030
                 viders.calendar,474,1,37,0,476,10036
                 ndroid.calendar,504,1,37,0,506,10019
         drmserver,38,1,1,0,39,1019
         mediaserver,39,1,1,0,40,1013
         installd,40,1,1,0,41,0
         keystore,41,1,1,0,42,1017
         qemud,42,1,1,0,45,0
         sh,45,1,1,0,46,2000
         adbd,46,1,1,554,49,0
                 sh,554,1,46,564,0,0
                         ptree_test,564,0,554,0,0,0
 kthreadd,2,1,0,3,0,0
         ksoftirqd/0,3,1,2,0,4,0
         events/0,4,1,2,0,5,0
         khelper,5,1,2,0,6,0
         suspend,6,1,2,0,7,0
         kblockd/0,7,1,2,0,8,0
         cqueue,8,1,2,0,9,0
         kseriod,9,1,2,0,10,0
         kmmcd,10,1,2,0,11,0
         pdflush,11,1,2,0,12,0
         pdflush,12,1,2,0,13,0
         kswapd0,13,1,2,0,14,0
         aio/0,14,1,2,0,24,0
         mtdblockd,24,1,2,0,25,0
         kstriped,25,1,2,0,26,0
         hid_compat,26,1,2,0,27,0
         rpciod/0,27,1,2,0,28,0
         mmcqd,28,1,2,0,0,0

Total entries: 51


Coding Style
=============
The code style used is consistent with that of the linux kernel coding style.
You can run the checkpatch.pl[1] with the arguments --no-tree -f [FILE_NAME]
to validate that the style was followed.

Example:
./checkpatch.pl --no-tree -f ptree.c

[1] - You can download checkpath script from: https://github.com/mirrors/linux-2.6/blob/master/scripts/checkpatch.pl