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Some knowledge about vdso

2012-01-04T16:45:00.001+05:30

As we can learn about linux gate or virtual dynamic shared object (VDSO) or linux-gate.so.1 or linux-vdso.so.1 by following page :
http://www.trilithium.com/johan/2005/08/linux-gate/
A lot of things explained in the above page, but when tried things, I faced some issues and solved as following :

1. Looking at ELF Auxiliary Vector
--> One can see all the ELF Auxiliary vectors on say 'true' binary as :
LD_SHOW_AUXV=1 /bin/true
This will actually execute the binary, and will show its ELF Auxilliary vector values.
2. It states that
a shared object exposed by the kernel at a fixed address in every process’ memory
Unfortunately, its no longer the case. When I tried getting the maps of vdso a couple of times :
cat /proc/self/maps | grep vdso
I always got the different address

3. Getting vdso segment.
As the above link says, dumping vdso can be done as :
Assuming the fixed mapping at 0xffffe000, the post tells you to use dd to extract the relevant information by accessing the process' pages through /proc/self/mem.
(Note that 0xffffe000/4096 = 1048574)

dd if=/proc/self/mem of=linux-gate.dso bs=4096 skip=1048574 count=1

but you will be surprised to get the following errors :
-- reading /proc/self/mem : I/O error
And no output..
Well, the reason of this error is stated beautifully in the following link :
http://unix.stackexchange.com/questions/6301/how-do-i-read-from-proc-pid-mem-under-linux
A good point made here is :
" since the first page in a process is never mapped (so that dereferencing a NULL pointer fails cleanly rather than unintendedly accessing actual memory), reading the first byte of /proc/$pid/mem always yield an I/O error."

Now then how should we dump vdso.... I then googled around ... found out the following post facing and solved the same issue I am facing :
http://anomit.com/2010/04/18/examining-the-linux-vdso/
He has actually created the following python script to get the vdso map of the current process, and seek to it in /proc/self/mem, and write down the required bytes to new file . Following is the script :
---------

#! /usr/bin/env python

from __future__ import with_statement
import re
import os

## regex pattern for finding out the memory address range from the output line
pattern = re.compile(r'[\w\d]+-[\w\d]+')

with open('/proc/self/maps', 'r') as file:
 for line in file:
  line = line.rstrip()
         if '[vdso]' in line:
   addr_range = pattern.findall(line)[0]
              start_addr, end_addr = [int(addr, 16) 
                                     for addr in addr_range.split('-')]
   break

file.close()
fd = os.open('/proc/self/mem', os.O_RDONLY)
os.lseek(fd, start_addr, os.SEEK_SET)
buf = os.read(fd, (end_addr-start_addr))
with open('linux-gate.dso.1', 'w') as file:
    file.write(buf)
    file.close()
os.close(fd)
------------------------

Another way to dump vdso, is to seek to address specified by ELF auxiliary vector AT_SYSINFO_EHDR, and dump 1 page (4096 bytes). Something like this :
-----------

#include 
#include 
#include 
#include 

static void *getsys(char **envp) 
{
   Elf64_auxv_t *auxv;
   
   /* walk past all env pointers */
   while (*envp++ != NULL);

   /* and find ELF auxiliary vectors (if this was an ELF binary) */
   auxv = (Elf64_auxv_t *) envp;
   
   for ( ; auxv->a_type != AT_NULL; auxv++)
     if (auxv->a_type == AT_SYSINFO_EHDR)
       return (void *)auxv->a_un.a_val;
   
   fprintf(stderr, "no AT_SYSINFO_EHDR auxv entry found\n");
   exit(1);
}

int main(int argc, char *argv[], char **envp)
{
   unsigned char buffer[4096];
   void *p;
   
   p=getsys(envp);
   fprintf(stderr, "AT_SYSINFO_EHDR at %p\n",p);
   memcpy(buffer, p, 4096);
   write(1, buffer, 4096);
}

What’s the Difference Between JPG, PNG, and GIF?

2010-10-06T10:41:00.000+05:30

Came across this really crispy knowledgeable article about various types of image files :
http://www.howtogeek.com/howto/30941/whats-the-difference-between-jpg-png-and-gif/

ubuntu and debugging abilities

2010-06-28T10:39:00.000+05:30

Today I came across following article by "KSplice" :
http://blog.ksplice.com/2010/06/attack-of-the-cosmic-rays/

Its a very nicely explained article for debugging a simple but ended in a complex problem.
There are lot of things to learn in the article -
First and foremost thing is .. Every single issue (big or small) has a reason, you just need to dig into the right direction.
- Ubuntu's work towards software debugging is going great. First time I have seen s/w management tools are helping so much in s/w debugging.
Do not ever ignore a small bit of details during debugging... It was just a bit flipping issue, but created a good amount of mess..

Aha! I just love systems programming/debugging and programmers ...

Nice piece of advice !!

2010-06-18T18:30:00.000+05:30

Wise people say we should always keep our eyes and ears open... I have been trying to do that a lot.... And heard a very nice piece of advice, when I was walking down the road saw an old fellow met with a young chap who probably just joined a job :
"You should never come out of your student mode. Should never sleep without reading at least for half an hour"..
What a thought it was, and how true.. Very practical and applicable to everybody.
On the similar lines, and old thought is -- "One should try to learn something daily" ..

Make a PDF book out of wikipedia

2010-04-20T13:38:00.001+05:30

I always was thinking of getting such a feature from wikipedia.. And here it is now. You can actually save the wikipedia pages as a pdf book and use it offline :

The steps are very very simple :

1. Log in to your Wikipedia account and activate the beta interface.

2. Once the new version is active, start the book creator tool inside Wikipedia.

3. Now open any Wikipedia page that would like to include in your PDF book and click the “Add this page to your book” link. Repeat this step until all the page have been added to the print basket.

4. Once you are done collecting Wikipedia articles, click “Show Book”, give it a title and hit the download button to save your book as PDF.

All PDF books created with Wikipedia are available under the Creative Commons License. And if you have no plans of printing Wikipedia pages, you may still use this trick to quickly download multiple pages from the world’s largest encyclopedia and read them offline on your mobile phone or your iPad.

Well, once you are at it, you can browse through your favourite pages, which wikipedia will find for you, and add them as you want and form your own book (the way you like it)...

I am sure people are going to luv this feature..

Reversing the roles...

2010-04-16T11:26:00.000+05:30

This is one of the most memorable and fun moment I had with my son...
Today when I was just lying near my kid who was eating Papad. Suddenly he started making very small pieces of papad and started putting on my mouth. It was exactly the same thing I used to do with him. The fun just started. Suddenly I thought of something, and started behaving exactly as he used to do, ie. started nagging about asking something and this and that and messing up things .. Then he started saying me "no no no" and waving his finger.. It was exactly the same way I do with him... Ufff.. what a fun!
I am amazed to see the kind of memory these kids have..

Running ubuntu on VirtualBox

2010-04-12T14:24:00.005+05:30

Thanks to one of my colleague, we got a very simple steps to install and run Ubuntu on virtual-box. This way one doesn't need to do a lot of jugglery to play with Linux system, be it kernel space programming or satisfying just simple Linux needs.
The benefits of running Ubuntu or any OS for that matter on virtual-box/vmWare or any other visualization equivalent are many. To name a few -
1. You can simultaneously access your windows box for using windows apps. Hence get most of both Unix and windows world.
2. No need to burn the CD to install ubuntu.
3. No need to worry about partitioning thingy (primary/secondary or extended or blah blah)
4. No mess up with MBR which gets rewritten when you install another OS.
5. It becomes very handy for showing software demo in linux, while parallely running much-tested-still-buggy MS solutions.
===================================================
I am yet to explore a few things on such a linux installation :
- Run a customized kernel.
- KERNEL Debugging ;)
- How would I access the files in windows drives ? [Solved: Explained after the installation part]
- Though I checked the sound which works, but I need to see if I can play a movie also, I dont
think there should be an issue, but just for completeness ;).
- I did try installing a couple of kernel modules and doing some stupid playing, and it worked
flawlessly till now.
===================================================

So here are the steps :

Prerequisites:

Will help if the machine has:

a processor with at least two cores
two-four Gb RAM
minimum of 40 Gb disk space (you can do with 20 - 30 too)

Since the guest uses networking etc from the host, you should not face installation issues.

Install VirtualBox

Head over to http://www.virtualbox.org, go to the Downloads sections and download/install VirtualBox for windows hosts. Once the install finishes you are ready to run Virtualbox and install your guest OS.

Once installed, run Virtualbox as Start->Programs->Sun Virtualbox->Virtualbox.

By default, Virtualbox will come up with no machines installed. And the only icon enabled will be the "New" icon in the pane on the left side of the UI.

Create Virtual Machine

Why use Ubuntu instead of the official supported RHEL? Well, Ubuntu is far simpler to install and beautiful, easier to run. Besides, virtuoso built on RHEL 4 works fine with Ubuntu 9.10. We will use the 32 bit version of the Ubuntu 9.10 here.

Let's create the machine.

Click New and follow the Wizard.

VM Name and OS Type page:

Name: Ubuntu_9_10
 OS Type
   Operating System: Linux
   Version: Ubuntu

Memory page:

Allocate half your RAM (or what you think you will need to run the virtual
 machine + your software).

Virtual Hard Disk page

Select Create new hard disk in Boot Hard Disk
 Alternatively, if you have an image created by somebody else
 (eg Tapan), select Use existing hard disk and browse/select that image.

Hard Disk Storage Type page

Select Dynamically expanding storage, it is the default anyways.

Virtual Disk Location and Size page

Here, browse and select the location of the hard disk image. For
 example, if D: has the requisite space, select D:\Ubuntu_9_10.vdi

At the end, you will be shown a Summary page.

Click Finish and the virtual machine will be created.

Install Ubuntu

Download latest ubuntu ISO image from http://www.ubuntu.com/getubuntu/download

Put this image somewhere on your windows hard drives.

Right click the virtual machine you just created and select Settings.

Click Storage in left pane.

On the right, a Storage page appears.

Select the CD image from the Storage Tree tree. The CD/DVD Device on the extreme right should be Empty.

Select the Browse folder icon.

In the Virtual Media Manager, navigate to the CD/DVD Images tab and click Add toolbar icon.

Browse to the Ubuntu iso and select it.

OK all the dialogs until you are back to the main UI.

Start the machine.

At this point, you will boot into normal Ubuntu.

Install the OS.

This includes installation and creation of a user. If you choose to create a user name same as your cadence login, be sure to edit the user info and match the uid/gid (after the OS is installed and you are running it).

Note: You always sudo in ubuntu. There's no root user by default.

Bring the OS up-to-date

Few useful commands are :

apt-get update

apt-get dist-upgrade

apt-get install

You will also need a couple of utilities.

$ sudo apt-get install gawk ksh
$ cd /bin
$ sudo ln -s /usr/bin/awk .

Run ubuntu on full screen

Once you have ubuntu running, you need to use the "Install guest addition.." option under the device menu to install the proper drivers on the guest and reboot the guest. Then do a Host+F and resize your guest using the "Display properties" to the res you like.

Share Windows drive to guest OS ie. ubuntu

0. Suppose you want to add "C:\shared" as the shared folder to your ubuntu.
1. Add folder(s) to shared folder menu.
   In ubuntu, Devices->shared folder add the shared folder name of the windows folder.
   Caution : 1. It should be the folder name, and not the drive only... as probably you cant share the complete drive.
   2. Have a different name than the shared folder name, otherwise you will get protocol error.

   Give "C:\shared" for windows shared folder, and give "my_share" in name box.

2. In ubuntu terminal :
   mkdir /mnt/windowsShare
   mount.vboxsf my_share /mnt/windowsShare
And you are done.

Running through creating tiny ELF executables. ...

2010-03-17T12:25:00.002+05:30

Came across these two wonderful posts mentioning about libc/gcc/linker and lot of interesting stuff . ....

http://www.muppetlabs.com/~breadbox/software/tiny/teensy.html

http://blog.ksplice.com/2010/03/libc-free-world/

These are worth reading for any programmer or system programmers at the least.

Hooking a syscall in linux >2.6.24 kernel..

2010-01-22T15:41:00.005+05:30

Just got hold of this while following some questions around.

It seems sometime since linux 2.6.24, the system call table in linux is been made read only, and one can not simply hook the system call table, just by loading the module. He will either have to recompile the whole kernel with the hook, or do the following

(Well, before that, in 2.6 kernel sys_call_table is no longer exported, so getting the address at run time is again another issue. Well, one can look at /boot/System.map file and find out the address of the system call, better to verify this address though)

So, since 2.6.24, following module will give kernel Ooops :

#include 
#include 
#include 
#include 

void **sys_call_table;

asmlinkage int (*original_call) (const char*, int, int);

asmlinkage int our_sys_open(const char* file, int flags, int mode)
{
   printk("A file was opened\n");
   return original_call(file, flags, mode);
}

int init_module()
{
    // sys_call_table address in System.map
    sys_call_table = (void*)0xc061e4e0;
    original_call = sys_call_table[__NR_open];

    // Hook: Crashes here
    sys_call_table[__NR_open] = our_sys_open;
}

void cleanup_module()
{
   // Restore the original call
   sys_call_table[__NR_open] = original_call;
}

The reason is same, the syscall table is read only. So either rebuild the whole kernel (bad option for regular dev.), or make the memory writable as following (Credit to somebody else, I am just copying their code ;)) :

#include 
#ifdef KERN_2_6_24
#include 
int set_page_rw(long unsigned int _addr)
{
    struct page *pg;
    pgprot_t prot;
    pg = virt_to_page(_addr);
    prot.pgprot = VM_READ | VM_WRITE;
    return change_page_attr(pg, 1, prot);
}

int set_page_ro(long unsigned int _addr)
{
    struct page *pg;
    pgprot_t prot;
    pg = virt_to_page(_addr);
    prot.pgprot = VM_READ;
    return change_page_attr(pg, 1, prot);
}

#else
#include 
int set_page_rw(long unsigned int _addr)
{
    return set_memory_rw(_addr, 1);
}

int set_page_ro(long unsigned int _addr)
{
    return set_memory_ro(_addr, 1);
}

Now Modify your code as :

void **sys_call_table;

asmlinkage int (*original_call) (const char*, int, int);

asmlinkage int our_sys_open(const char* file, int flags, int mode)
{
   printk("A file was opened\n");
   return original_call(file, flags, mode);
}

int init_module()
{
    // sys_call_table address in System.map
    sys_call_table = (void*)0xc061e4e0;
    original_call = sys_call_table[__NR_open];

    set_page_rw(sys_call_table);
    sys_call_table[__NR_open] = our_sys_open;

    set_page_ro(sys_call_table);
}

void cleanup_module()
{
   // Restore the original call

   set_page_rw(sys_call_table);
   sys_call_table[__NR_open] = original_call;

   set_page_ro(sys_call_table);
}

Books Wish List

2009-09-24T10:55:00.006+05:30

I think everyone should have a reading wish list, I just thought of preparing one for myself.. Will keep adding the books into this list ..

1. Coders at Work -- almost a 5 starred book.. 60 mins. Interview of 15 selected programmers (including knuth, ken thompson) -- Sounds very interesting.

2. Thriving in tough times. -- This book is the real deal for thinking people with real problems, containing 39 tools you can use at any time to boost your productivity and brighten your mood, even in the face of tough problem

3. Beautiful Code: Leading Programmers Explain How They Think

4. Ifferisms: An Anthology of Aphorisms That Begin with the Word "IF"

5. The Elements of Style -- A good book for everyone...

6. The Design of Design (Essays from a computer scientist) -- From the writer of "Mythical man month" which is one of my favourite books.
......

troubleshooter.com

2009-09-24T10:53:00.003+05:30

Doing a lot of browsing after a long time today, and finding lot of interesting sites as well.. --
www.troubleshooters.com is one such site, containing a looooottttts of information.. maybe a good quick guides for interview aspirants.

Happy Reading.

Run with Ubuntu in a thumb drive

2009-09-24T10:48:00.002+05:30

I have a 2 GB micro sd card, and a compatible usb reader for it... Was just thinking a day, if I could load an OS in it ?
And guess what, stumbled on to this nice article on making a bootable usb drive for ubuntu.
http://www.ghacks.net/2009/09/24/how-to-create-a-bootable-usb-ubuntu-drive/
It just sounds amazing to see how technology is growing. Gone are the days of floppy disks, and then CD ROMs which are difficult to carry in a small pocket. A usb drive of few gigs can change the life :)..

sx4 is being tested ....

2009-07-23T12:30:00.003+05:30

The dude has decided to test the vehicle from outside before getting in...
My bro is trying hard to get clearance from this test ;) ...

Frustration

2009-02-20T15:13:00.005+05:30

Hi,
At the end of every day I feel frustrated, for not able to accomplish what I plan to do. Why ?
Hah, there are so many things I need to do, not only for betterment of my professional career, but also to grow personally. But at the end of the day, I ind my self standing at the same place I was at the start of this day. Not that I dont have enough time to do all this, but I dont have enough energy to do the things ... No encouragement, no enthusiasm, no motivation, no ...... blah blah...

Need to read a lot. To keep up with the technology, more important to remain in the job atleast in this recession time.
Want to read a couple of good novels.. But ..........
Want to do exercise daily ... But .......
Want to see movies ... But .........
Want to write some good code ... But ...........
Want to shop for my kid ... But ..............
Want to find peace somewhere ... But ........
Want to invest in tourism .. But ...........
Want to write some good post in the 'space' ... But ....
Want to ................................................. But ...............

Dont understand where this 'But' is leading me to... But I want to get away with this "But" somehow.
Hey, I think I am getting inspired by this now ... Need to get back to work to get over with this never ending 'But' series ...!!!!

I think frustration is part of everybody's life, but it matters only in terms of handling it. Some people go into depression, while some get inspired by it :)..

Yet another stupid post .....!!!!

New mantra for the success

2008-12-22T18:02:00.002+05:30

"Learn from your failure, and get success" is an old mantra .. The improvised version is --
"Learn from other's success, and be successful !!!"

The whole industry seems to be be following the new mantra... however, one should be very careful in learning the success mantras from others.. because what works for someone, may not work for everyone ;)

-

Do Not Disturb !!!

2008-12-11T13:05:00.004+05:30

After much fun with not-so-friendly calls with very friendly voices, my patience timed out, and I thought of registering my cell number with Do-Not-Disturb service from Vodafone.

One fine query to google gave me the page where I got the information about Do-Not-Disturb Service. I had multiple options to do that --
o1- Register my number online
o2- SMS

o3- call up some tollfree number of 4 digit

Ofcourse the best option was 'o3' for obvious reasons. So I called up. Again a sweet voice turned up the other side... And I told her my requirement. She said it can be done after confirming a few things from me. Then she said it will take atleast 45 days to register my number for this service... I was shocked to hear that. In such a jet age, how can this be possible. Well, she explained me, that they will circulate my number all over india, and thats how it works. Ofcourse her logic didnt satisfy my reasoning, but I stayed quite. I wanted to quickly get over with this.

Then she explained me, if I ever want to deregister with it, I will have to wait for another 90 days for it, and then it will take another 45 days for me to deregister :)) .. The fun was just starting...
Well there was more to it. She said, even after registering, if I get a unwanted call, I will need to give that number to Vodafone people, and it will take another 20 days for me to stop getting calls from that number .......... :)

I said ok, please go ahead and populate my number all over india, and register me for all possible junk calls...

She finally said - "Ok, Mr. Maneesh. Congratulations !! Now you will not get any promotional calls/ unwanted calls from various people", and I said "Thank You very much" ..

She then said "Mr. Maneesh I understand you are a very valuable customer to us, and we have this offer particularly for you from vodafone .......................................................... " I was shocked, and told her .. Mam, I have just registered my phone number for no promotional calls, and you are just giving me another promotion.... what kind of quality you have ? ...

Oh! It was so much of fun, but I still do wonder..... Do people really understand the meaning of any service ?

First glimpse of my little one

2008-11-26T15:31:00.005+05:30

I am writing here after a long time... infact after since I joined the new company... Well all other posts will follow but this is going to be about the best ever feeling I got :-

It was about 8:20 pm on Nov. 2nd, 2008. I was standing just next to the operation theater, when the nurse came and handed him to my mom..... Yes, it was the little Me.... MY SON, Mini-me... PooPoo, Kuchchu and what not !!!!
I thanked the god, for the blessings and for the successful delivery, I do wanted to thank my wife also for the same.

Then I looked at my son, and kept looking, couldnt just remove my eyes of him, his full body was all white, and I was wondering whether all kids with 5 minutes of age look like this, or this is just my kid who is so white :).. weird no !!! There were a storm of thoughts with happiness in my mind... its difficult to put here.

Well, all the recently born kids (newly born are older than recently born) look white because of the environment they come from...

I looked at his small and delicate hands, eyes, face ..... was damn scared to even touch him. I washed my hands atleast twice before touching him.

His hands got familiar with new environment.. and became little raddish, and slowly his whole body looked much better.

Slowly he opened his beautiful eyes, and it was so fun... I immediately wanted to talk to him :))
Well, he didnt even know how to cry at that time, he was just taking some hicc-ups and sneezing also ....... and was making some noises with very small decibel units.

That night, I stayed in the hospital, with my mother, and my wife was unconscious due to sedatives, and mini-me. And guess what, I didnt sleep that night, not because I was worried about him... but because I was so happy, and was talking to my mom just about everything. Beech beech mein mini-me bhi kuch kuch bol deta tha...

And that night itself, just when he was about 8 hours old, he learned the art of crying .. I would say, that is the first thing mini-me learned. And I dont need to specify that the kid has mastered this art next day itself :)

I guess it was the feeling of the lifetime for me. And it was the best night so far.... And I am thankful to God for the blessings. My wife for this wonderful gift ... My parents, my brother and all my friends whose support and wishes is always there with me.

Hopping to the next company ....

2008-06-04T14:11:00.005+05:30

After working in a small company (Rimo Technologies) during my training days, working in BIG HP for 5 good years was lots of fun, and learning. After HP I joined another startup Solidcore in August 2005.

Well, I decided to leave this company also about a year back ... revised the same thought 6 months ago.. Now is the time when I have communicated my decision to the management, and moving to Cadence which is a big company again.

My time here cannot be compared at all with the time I spent in HP. It was more of a compromise of staying near to my native, than working in a great company with great work and blah blah... I did not learn a lots here, because the technology remained same between my work @HP and work @SC. However, I did learn working in tight situations, also fetching help from internet rather than from people around me.

Last days here are kind of boring.. except chatting friends, reading a bit, and finishing off some work. Have got no motivation left of working here.

I am getting a sense of working away from some of the friends I made here, but then I had experienced this feeling while leaving HP too.

Well, I am going to join another big company after another small company... dont know how it is going to work out.. I am very very confused about lot of things ...
I am little tensed that I am changing the technology and domain I worked in for more than 7 years. Dont know what is going to happen in the future. Looks like I will not do the work I love in CS anymore. Am I sad ? But how far I could have gone.. "People with 9-10 years of experience in India are suppose to be managers and not programmers". The road ahead looks hazy.. and I have left everything on luck.

I still wonder, do people change their strengths after 7+ years of experience ?

I am hoping for the best .....

Lost in Michigan

2008-06-04T11:49:00.005+05:30

I had to travel to Auburn Hills, Michigan on a very short notice and for a short duration (1-2 week) for some Solaris problem at GM site.

I landed up at Detroit Metro Airport, and then took a taxi to my hotel Courtyard Mariott, Opdyke Road, Auburn Hills. The hotel was comfortable and lonely as ever. The admins had booked a rental-car for me at Airport, but I was in no mood to take the rental car services more because I wasnt comfortable with routes, and infact was scared that I might have forgotten right side driving.

Next day one of the sales engineer (E J Pappas) came to my hotel to take me to GM site. The bad news he gave me is that he will not be available in the town for the week after today, so I will have to take the car to be mobile over there. He said he will make the arrangements, and I told him I wanted a car with GPS only because I am unfamiliar with the roads out there, and he agreed to that. The hotel was about 7-8 miles from the GM office. After introducing me in the office, EJ went to arrange things for me.. and he arranged to send car directly at the office location.

After a while, Cary (GM Person I was working with), got a call that the car is ready and is standing in the parking lot. It was a Mustang. We both went outside, and found out that the car didnt have GPS.. I immediately said, I cant drive a car without GPS, I was too scared of driving at unknown roads. But the car rental officer said one can get a GPS driven car only at airports which is about 40 miles from GM office. EJ was gone to his next business after making all the necessary arrangements for me.

Cary, and EJ gave me all the required driving directions (to hotel, to office, and to near by locations).. and I had surfed google earth too. On the way back to hotel, Cary escorted me and showed me the way to hotel. Till that time I became comfortable with right side driving, as I had driven in US in the past.

Cary had given me some good instructions, like what to do and what not to do.. and one was -- not to enter in the business loop in detroit, or else I can be stuck there forever. Business loop can be identified by I-75 marked with green color. I remembered all the instructions, and noted down cary's number for urgency.

I comfortably reached hotel at 5:00 pm in the evening. Well, then I thought of going to a Target Store (which EJ showed me in the morning) to get some recharge for my local phone. I looked at all the directions in google maps, and then left hotel at 5:30 pm. The target store was suppposed to be 13 miles or 15 mins away from hotel, and I expected to reach there by 6:00 pm, and came back to hotel by 7:00 pm. Well, I was driving till 6:15 for Target but didnt find, and figured out soon that I lost it, So I took a U turn, and started back for hotel. I dont know but somewhere I missed one diversion, and then I suddenly found that "I AM LOST IN MICHIGAN".. At 7:00 pm, I parked the car and asked somebody about the road (Opdyke Road), and started again towards the direction I got. But not very late I found out that I am running in Business Loop :(, Remember Murphy's Law . It was 8:00 pm, and it started drizzling. I again parked the car near one beer shop, and asked somebody, he gave me another direction, and I started again... I was completely lost.. I opened the paper map, Cary gave me... and I couldnt get where I am. I found a Gas Station. I asked there, he told me I am driving in wrong direction, so I started going back.. My complete direction sense was gone. I was thinking of parking the car and sleeping over there only. But something was telling me that I am not very far from Hotel or Opdyke road.. I parked the car again, and suddenly I found out, I am running the car without head lights ON. Thats it, this was a new problem.. if a cop catches me, I am gone forever. I took about 15 mins. to find out how to turn ON the lights. It was very hazy outside, because of rain and clouds. And I was at a very small street. Then I found one McDonald store, and he gave me complete directions, told me that some road is bad, so gave alternate route, and that was it.. after struggling for another 15 mins. I was at Opdyke road. I finally reached hotel at 10:30. And it was a horrible experience. But then the outcome was that I now remembered all the streets, and memorized complete Detroit map, and cannot get lost again :).

It was one memorable experience for me.. more than an adventure. Was telling the story to my boss in US office, and he told me thank god I was not driving till Detroit city, otherwise I could have got into Canada Tunnel, and could have reached Canada without Visa.. and this post could have become much larger :)).

Thanks for your patience reading, it gives me a morale boost for one more such trips ;)

Programmer Poetry

2008-04-17T16:25:00.002+05:30

Couldnt resist myself pasting the image in my own blog. This is a very clean way of explaining a programmers life.
I often ask myself... Do I love my life ? Do I love my job ?
Do I ...... blah blah!... I am confused.. as every programmer is.

enable sysrq keys

2008-01-24T15:41:00.000+05:30

Enable sysrq keys by putting following entry into /etc/sysctl.conf file -
kernel.sysrq = 1

Now reboot the system and see sysrq keys in effect -
Press Sysrq <-- will follow your command.
command can be :
'v' : for help .. The most needed
'b' : for boot
'c' : To crash the system
....
....

Linux... Recover automatically from panic

2008-01-24T15:38:00.000+05:30

Normally when a linux system panics, it halts, and one needs to manually press the power button to reboot the system, and this irks at times... specially when you are sitting far from the system. So the solution is to do the following-

edit the /etc/sysctl.conf file, and put following line -
kernel.panic = 5

This will force the system to reboot after 5 seconds after it dumps the crash, and you are saved from touching the system :)

Save system crash on linux

2008-01-24T15:30:00.000+05:30

Documents referred :

http://fcp.surfsite.org/modules/smartfaq/faq.php?faqid=1255

http://www.redhatmagazine.com/2007/08/15/a-quick-overview-of-linux-kernel-crash-dump-analysis/

http://people.redhat.com/anderson/crash_whitepaper/

Saving Crashdumps can be useful many times for postmortem ananlysis on linux panics.

Linux is particularly not very popular when we (read kernel engineers) talk about kernel debugging. Linus always believed in writing perfect software, huh!. Anyways, here is one way of dumping the memory and analyzing it at later point and learn something useful :)

We can configure diskdump for dumping the memory incases of crash dumps in linux. The dumps generated by diskdump are kept in /var/crash directory, by name vmcore, and these dumps can be analyzed through crash utility. The only requirement of this whole setup is that crash requires 'vmlinux' file (the kernel which has panic'ed).

Setup diskdump:-

Install diskdump packages - ftp://rpmfind.net/linux/fedora/core/updates/3/i386/diskdumputils-1.1.7-3.i386.rpm
Compile kernel with debug info ON <-- google can give
Install the new kernel and save the vmlinux file in a known location
Boot with the compiled kernel.
modprobe diskdump <-------- load the diskdump module
configure a dump device by giving diskdumpfmt command

One can configure a swap partition for diskdump ...

$ diskdumpfmt -cv /dev/sda3 <------- Will check if device can be configured or not

$ diskdumpfmt -fv /dev/sda3 <-------- Will format the device for diskdump

$ vi /etc/sysconfig/diskdump and put DEVICE=/dev/sda3

$ service diskdump restart

$ cat /proc/diskdump <---- will show all parameters of diskdump configuration (it should show the device also) like -

# sample_rate: 8

# block_order: 2

# fallback_on_err: 1

# allow_risky_dumps: 1

# dump_level: 0

# compress: 0

# total_blocks: 259722

sda3 128520063 4016187

Now since diskdump is configured, next step is to test whether dump is really collected or not.

$ vi /etc/sysctl.conf

# This will enable the sysrq keys for forcibly panicing the system etc.

kernel.sysrq = 1

# following line will force the system to reboot after 5 seconds if the system crashes after some panic. By default the system halts after it panics.

kernel.panic=5

* Crash the system -

echo c > /proc/sysrq-triggered <-- This will crash the system forcibly

press the sysrq key -- Sysrq C # all keys pressed together.

This will crash the system. Note that by putting “kernel.panic=5” the system will reboot automatically after 5 seconds.

Now while booting up, since diskdump is configured, it will dump the crash stored in the dump device (swap in our case), and comes up.

Analyzing the Crash

Install crash package -- ftp://rpmfind.net/linux/fedora/core/4/i386/os/Fedora/RPMS/crash-3.10-13.i386.rpm

go to /var/crash/ directory.. you will find vmcore file here...
file vmcore ---- will show that its a core file
strings vmcore | grep 'Linux' <-- will show which vmlinux file has generated this dump.
run crash /boot/vmlinux /var/crash//vmcore

This will give you enough information about the core --
Some commands are -

There are many commands in crash. It is also possible to extend crash by adding new commands, by writing new code and compiling it into the crash executable, or creating a shared object library that can be dynamically loaded by using the extend command. The following are some commonly used crash commands that you will likely use:

help – get help
crash has a readily available help information built into the utility, by typing help. Each command has its own man-like page, which can be viewed by typing help command-name.

crash> help   *      files   mod    runq   union alias  foreach mount  search vm ascii  fuser   net    set    vtop bt     gdb     p      sig    waitq btop   help    ps     struct whatis dev    irq     pte    swap   wr dis    kmem    ptob   sym    q eval   list    ptov   sys exit   log     rd     task extend mach    repeat timer   crash version: 4.0-3.3   gdb version: 6.1 For help on any command above, enter "help “. For help on input options, enter “help input”. For help on output options, enter “help output”.

Tip: all the crash commands can be piped to external programs or redirected to files:

crash> log > log.txt

This will send the in-kernel log to a local file called log.txt.

crash> ps | fgrep bash | wc -l

This will count the number of bash tasks that were running.

sys – system data

crash> sys        KERNEL: /usr/lib/debug/lib/modules/2.6.9-22.EL/vmlinux      DUMPFILE: /home/eteo/crash/127.0.0.1-2007-04-30-21:38/vmcore          CPUS: 1          DATE: Mon Apr 30 21:38:40 2007        UPTIME: 00:04:04  LOAD AVERAGE:  0.36, 0.23, 0.08         TASKS: 36      NODENAME: localhost.localdomain       RELEASE: 2.6.9-22.EL       VERSION: #1 Mon Sep 19 18:20:28 EDT 2005       MACHINE: i686 (1862 Mhz)        MEMORY: 1 GB         PANIC: "Oops: 0002 [#1]" (check log for details)

The sys messages have information of the system (e.g. kernel release, kernel version, number of CPUs, amount of memory, etc), the time of vmcore taken, the operating period, and the panic (e.g. oops type, panic task/PID/command, etc).

bt – backtrace

crash> bt PID: 2857   TASK: f7b677f0 CPU: 0    COMMAND: "bash"  #0 [f7191e04] start_disk_dump at f89d7bb3  #1 [f7191e18] die at c010682e  #2 [f7191e48] do_page_fault at c011ab00 [...]  #9 [f7191fc0] system_call at c030f918     EAX: 00000004 EBX: 00000001 ECX: b7de7000 EDX: 00000002     DS: 007b       ESI: 00000002 ES: 007b        EDI: b7de7000     SS: 007b       ESP: bfe01650 EBP: bfe01670     CS: 0073       EIP: 003297a2 ERR: 00000004 EFLAGS: 00000246

log – dump system message buffer

crash> log [...] SysRq : Crashing the kernel by request Unable to handle kernel NULL pointer dereference at virtual address 00000000  printing eip: c0233fa7 *pde = 3e9f3067 Oops: 0002 [#1] Modules linked in: md5 ipv6 autofs4 i2c_dev i2c_core sunrpc scsi_dump diskdump dm_mirror dm_mod button battery ac yenta_socket pcmcia_core uhci_hcd ehci_hcd shpchp snd_intel8x0 snd_ac97_codec snd_pcm_oss snd_mixer_oss snd_pcm snd_timer snd_page_alloc snd_mpu401_uart snd_rawmidi snd_seq_device snd soundcore ipw2200 ieee80211 ieee80211_crypt tg3 floppy ext3 jbd ata_piix libata sd_mod scsi_mod CPU:    0 EIP:    0060:[]    Not tainted VLI EFLAGS: 00010246    (2.6.9-22.EL) EIP is at sysrq_handle_crash+0×0/0×8 eax: 00000063   ebx: c0370db4    ecx: 00000000  edx: 00000000 esi: 00000063   edi: 00000000    ebp: 00000000  esp: f7191f60 ds: 007b   es: 007b    ss: 0068 Process bash (pid: 2857, threadinfo=f7191000 task=f7b677f0) Stack: c02342d8 c032dc4e c032f105 00000003 00000002 f7b6adc0 00000002        f7191fac c01a8a13 c0362740 c0168205 f7191fac b7de7000 f7b6adc0        fffffff7 b7de7000 f7191000 c01682cf f7191fac 00000000 00000000        00000000 00000001 00000002 Call Trace:  [] __handle_sysrq+0×58/0xc6  [] write_sysrq_trigger+0×23/0×29  [] vfs_write+0xb6/0xe2  [] sys_write+0×3c/0×62  [] syscall_call+0×7/0xb Code: 4c 11 42 c0 05 00 00 00 c7 05 50 11 42 c0 2f cc 31 c0 c7 05 54 11 42 c0 00 00 00 00 c7 05 58 11 42 c0 00 00 00 00 e9 e5 0b f0 ff  05 00 00 00 00 00 c3 e9 e1 59 f3 ff e9 1e bc f3 ff 85 d2 89

The log command dumps the kernel log buffer contents in chronological order. This is similar to what you would see when you type dmesg on a running machine. This is useful when you want to look at the panic or oops message. An oops is triggered by some exception. It is a dump of the CPU register’s state and kernel stack at that instant. From the panic message, we can find hints as to how the panic was triggered (e.g. the function or process or pid or command or address that triggered the panic), the register’s information, kernel module list, whether the kernel is tainted with proprietary kernel modules loaded, and so on. Let’s walk through the panic message to see what we can learn from it. See the comments below each section within the log:

crash> log [...] SysRq : Crashing the kernel by request <-- this panic is intentional Unable to handle kernel NULL pointer dereference at virtual address 00000000

This is the address to which reference was attempted.

 printing eip: c0233fa7

This is the address at which the failure occurred.

*pde = 3e9f3067 Oops: 0002 [#1]

Often one oops will trigger more; only the first is reliable.

Modules linked in: md5 ipv6 autofs4 i2c_dev i2c_core sunrpc scsi_dump diskdump dm_mirror dm_mod button battery ac yenta_socket pcmcia_core uhci_hcd ehci_hcd shpchp snd_intel8x0 snd_ac97_codec snd_pcm_oss snd_mixer_oss snd_pcm snd_timer snd_page_alloc snd_mpu401_uart snd_rawmidi snd_seq_device snd soundcore ipw2200 ieee80211 ieee80211_crypt tg3 floppy ext3 jbd ata_piix libata sd_mod scsi_mod CPU: 0 EIP: 0060:[]    Not tainted VLI

The first part is the code segment and instruction address. If tainted, it will be followed by:

               G – All modules loaded have a GPL                or compatible license                P – Proprietary modules loaded                F – Module forcibly loaded                S – Oops on hardware that are not                SMP capable                R – Module forcibly unloaded                M - Machine Check Exception (MCE)                occurred                etc (see Further readings section). EFLAGS: 00010246    (2.6.9-22.EL)

This line denotes program status, registers information.

       f7191fac f7191000 c01682cf f7191fac 00000000 00000000 00000000        00000001 00000002  Call Trace:

This is the backtrace of function calls.

 [] __handle_sysrq+0×58/0xc6  [] write_sysrq_trigger+0×23/0×29  [] vfs_write+0xb6/0xe2  [] sys_write+0×3c/0×62  [] syscall_call+0×7/0xb Code: 4c 11 42 c0 05 00 00 00 c7 05 50 11 42 c0 2f cc 31 c0 c7 05 54 11 42 c0 00 00 00 00 c7 05 58 11 42 c0 00 00 00 00 e9 e5 0b f0 ff  05 00 00 00 00 00 c3 e9 e1 59 f3 ff e9 1e bc f3 ff 85 d2 89

From the line c0233fa7, we can see that this is the address at which the failure occurred. Issuing the following command can give us more hints as to which function or source code or assembly statement in the kernel triggered that:

crash> dis -lr c0233fa7 /usr/src/build/614745-i686/BUILD/kernel-2.6.9/linux-      2.6.9/drivers/char/sysrq.c: 115 0xc0233fa7 :        movb   $0×0,0×0

ps – display process status information

crash> ps    PID    PPID CPU   TASK   ST %MEM  VSZ  RSS COMM       0      0  0 c0358be0  RU  0.0    0    0 [swapper]       1      0  0 f7e01770  IN  0.1 1680  684 init [...]    2380      1  0  f7ac2800 IN  0.0 1604  504 mingetty    2769   2371  0  f7ac3970 IN  0.2 5740 1636 bash    2852      1  0  f7b1a880 IN  0.2 4240 2012 sshd   2855 2852 0 f7b66680 IN 0.3 8316 2756 sshd > 2857 2855 0 f7b677f0 RU 0.2 6260 1628 bash   Sometimes it is useful to know which process belongs to which parent or vice versa. ps has -c and -p to show the child and parent processes.  crash> ps -p 2857 PID: 0       TASK: c0358be0 CPU: 0    COMMAND: "swapper"  PID: 1       TASK: f7e01770 CPU: 0    COMMAND: "init"   PID: 2852    TASK: f7b1a880 CPU: 0    COMMAND: "sshd"    PID: 2855    TASK: f7b66680 CPU: 0    COMMAND: "sshd"     PID: 2857    TASK: f7b677f0 CPU: 0    COMMAND: "bash"

files – open files

crash> files PID: 2857    TASK: f7b677f0 CPU: 0   COMMAND: "bash" ROOT: /     CWD: /root  FD    FILE      DENTRY    INODE   TYPE  PATH   0 f7a6e7c0 f7790198 f7b0fdcc     CHR   /dev/pts/0   1 f7b6adc0 f7190130 f7b9ca4c     REG   /proc/sysrq-trigger   2 f7a6e7c0 f7790198 f7b0fdcc     CHR   /dev/pts/0  10 f7a6e7c0 f7790198 f7b0fdcc     CHR   /dev/pts/0 255 f7a6e7c0 f7790198 f7b0fdcc     CHR   /dev/pts/0 crash> files 2852 PID: 2852    TASK: f7b1a880 CPU: 0   COMMAND: "sshd" ROOT: /     CWD: /  FD    FILE      DENTRY    INODE   TYPE  PATH   0 f7b336c0 f78001d8 f7cb1ba4     CHR   /dev/null   1 f7b336c0 f78001d8 f7cb1ba4     CHR   /dev/null   2 f7b336c0 f78001d8 f7cb1ba4     CHR   /dev/null   3 f7b69600 f7bf5280 f7aadafc     SOCK  socket:/[6277]

dev – device data

crash> help dev [...]  If no argument is entered, this command dumps the contents of the  chrdevs and blkdevs arrays. crash> dev CHRDEV    NAME         OPERATIONS  1      mem              (none)  4      /dev/vc/0        (none)  4      tty              (none) [...] BLKDEV     NAME        OPERATIONS  1      ramdisk        c0376d08   2      fd            (unknown)  8      sd             f880e070

Read the white paper of core for more commands about crash -- http://people.redhat.com/anderson/crash_whitepaper/

Some fishy stuff...

2007-10-24T16:01:00.000+05:30

If you are in Linux and running gnome, do the following -
Alt-F2 and type "free the fish" and you get a great company on the monitor :)
You can try clicking on the companion.

Couldnt find which process this is running ????

A couple of unsolved ones .... plz solve `em

2007-09-17T09:51:00.001+05:30

I have been trying a couple of questions (mentioned below), but didnt get a good hit uptill now...... I request readers also to make some good attempts, and provide answers if they could.. thanks!

1. A machine starts flipping a fair coin. It halts after 2n flips if and

only if the last n flips were all heads. Otherwise, it continues
flipping. For example, each of these would be complete flipping
sequences:

HH
TH
HTHH
HTTHHH
TTHTHHTHHHHHHH

What is the probability that the machine eventually halts?

Some good 'U' and some good 'K' questions...

2007-09-14T16:30:00.000+05:30

I am trying to collate some good Unix and some good kernel questions... Will start with writing only questions here, but as and when I find time I will fill up the answers as well... BUT hope that free time comes sooner than later ;)... Have fun!

The list will keep growing. I request the readers also to put their answers to make the best use of the post. Thanks!

[Some are picked from coolinterview.com]

- How does the kernel differentiate device files and ordinary files?
- what is kernel?
2. what is the difference between kernel and microkernel?
3. what is the difference between unix and Linux?
- Explain the steps that a shell follows while processing a command.
- How to terminate a process which is running and the specialty on command kill 0?
- What is a pipe and give an example?
- What are the difference between Daemons in Unix and service processes in Windows?
- What is the difference between soft link and hard link in unix ?
- Explain the UNIX Kernel.
- What is Concurrency? Explain with example Deadlock and Starvation.
- What are your solution strategies for "Dining Philosophers Problem”?
- Explain Memory Partitioning, Paging, Segmentation.
- Explain Scheduling.
- What is Semaphore?
- Explain the following file systems : NTFS, Macintosh (HPFS), and FAT.
- What are the different process states?
- What is Marshalling?
- Difference - Loading and Linking?
- Do you have idea about "Shell Job Control"?
- Exlain Stickybit?
-
-
-

Solve Me !!

2007-09-14T13:53:00.000+05:30

What is the beginning of eternity, the end of time and space, the start of every end, and the end of every race?

Delete duplicate mails

2007-08-17T09:19:00.000+05:30

Many times I have found myself playing with thunderbird settings, and/or juggling around with it.... and ended up with having multiple downloads of the same mail from the server. The reason being, I dont delete mails at the server when I download them at my desktop.. which is a good habit.
Anyways, the problem is to have a clean inbox with atmost one copy of each mail. I just thought of using the popular verb and finding out on my own (Btw, I use thunderbird mail client). ...... Great, the problem is faced by many and so the solution is found (re-using solution ... rocks!) -- http://www.ghacks.net/2007/05/18/automatically-remove-duplicate-mails-in-thunderbird/
explains how to do it by just setting internal variable ;).. Well, you can infact tweak many more things in thunderbird now ... Have fun !

Complicated Toilet Seat Problem

2007-06-04T11:29:00.001+05:30

Wondering how the simple things can be made complicated ... Read out -
http://www.scq.ubc.ca/the-social-norm-of-leaving-the-toilet-seat-down-a-game-theoretic-analysis/

Thinking .... What is the culprit for the complications --
1) The Scientists involved in this useless(yet usefull) research.
2) The toilet seats... Na to toilet seat hoti .. aur na hi problems ;)
3) Mathematis .... .......... Mathematics can enter anywhere.. why leave toilet seats.
4) Marriage ---- This you can find out only after reading the article .. After this is the root of all good or bad things in life ;)

Enjoy!

Good habits on Unix

2007-06-01T12:58:00.000+05:30

http://www.ibm.com/developerworks/aix/library/au-badunixhabits.html

Quite helpful

Finally something on AIX filesystems

2007-06-01T12:51:00.000+05:30

Since the time, I looked into AIX systems, I have wondered the AIX file system framework. Read a bit about that in docs, but confused more.. as I used to be ..!! gfs/gnode interface was never clear to me. vfs/vnode are not so clear as in Solaris and HPUX. Today I came across the following article.. and things are becoming clearer now ..........

http://www.ibm.com/developerworks/aix/library/au-aixfilesystem/?ca=dgr-lnxw07aixfileframe

Still there are many hiccups on the way of understanding it completely.. it is much better. I am in discussion with concerned people, will add the conclusion to this article.

Marriage does wonders..

2007-05-30T17:13:00.001+05:30

Ppl say marriage does wonders.. :) I am yet to see. But all I can say right now is that wonders start much before that ;)...

More thoughts are still uncooked.. coming soon ..

Kernel programming from a philosophical viewpoint

2007-05-30T17:11:00.000+05:30

Thoughts are in process ................ coming soon !

2007-05-22T12:21:00.000+05:30

Data Structures and Algorithms:

* Find the loop in a linked list and fix the cycle.
very good explanation and soln. are given in :
http://www.tekpool.com/?p=16
http://k5rec.blogspot.com/2006/12/c-programming-removing-loop-from.html

Though I am yet to work out on the solutions.. But theoritically they look perfect.

A scratch on the data structures (Live)

2007-05-21T09:08:00.000+05:30

Found some good data structures (thinking!) questions.... Possible answers follow the question.

1. A string stored in a singly linked list. Find a best (space + time) way to find if string is a palindrome string - "A string can be called palindrome, if it is same from forward and backward". Assume the length of string is known.

A1: Store the string into an array and then start comparing from both end points until the pointers meet each other.

A2: Push the link list elements into a stack until midpoint, and then starting popping them while other pointer traverse and compare from midpoint to end.

A3(Best Soln): Reverse the link list till the midpoint, and then compare first element with middle element and so on.

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

ek chidiya, anek chidiya

2007-05-10T14:26:00.000+05:30

The days when I used to love life ........

Doordarshan rocks, atleast not spoils the life ..

Feisty Fawn

2007-04-20T23:18:00.000+05:30

There you go with another Ubuntu release 7.04, the FEISTY FAWN.
It was a breeze to install, though I had some problems while I upgraded from edgy. But fresh installation was as cool as ever. After that first noticeable cool thing was the splash gnome window, the opaque startup window was giving a good feel.
Then I started experimenting with new features, like configuring wireless by new network-manager.. was easy. In edgy I needed to install wifi-radar to have almost similar feature, but now I dont think I need.
Running media files without pre-installing the codecs (having a trouble of finding the codecs) was again a nice addition.
Desktop effects, was a nice eye candy, but it was very limited after I had a wonderful hooked up experience with beryl. I think beryl should have been a default app. in this release. I hope it will be in next for sure.

I am yet to check out the real addition on kernel 2.6.20 ie. kernel virtualization, but I am sure it is going to be as perfect as linux is. Overall I am happy to upgrade to 7.04.

UBUNTU ROCKS !!!

Came across nice tips for ubuntu lovers ... http://www.pcworld.com/article/id,130923-page,1-c,linux/article.html

Having fun!

The Toilet example

2007-04-17T14:28:00.000+05:30

Found a real life example when you want the difference between Semaphore and Mutex. The example is called as "The toilet example".

Not to temper with copyrights, access the link : http://koti.mbnet.fi/niclasw/MutexSemaphore.html

However, the contents are as follows (incase the link is down sometime) -

Mutex vs. Semaphore, what is the difference?

The Toilet Example (c) Copyright 2005, Niclas Winquist ;)

Mutex:

Is a key to a toilet. One person can have the key - occupy the toilet - at the time. When finished, the person gives (frees) the key to the next person in the queue.

Officially: "Mutexes are typically used to serialise access to a section of re-entrant code that cannot be executed concurrently by more than one thread. A mutex object only allows one thread into a controlled section, forcing other threads which attempt to gain access to that section to wait until the first thread has exited from that section."
Ref: Symbian Developer Library

(A mutex is really a semaphore with value 1.)

Semaphore:

Is the number of free identical toilet keys. Example, say we have four toilets with identical locks and keys. The semaphore count - the count of keys - is set to 4 at beginning (all four toilets are free), then the count value is decremented as people are coming in. If all toilets are full, ie. there are no free keys left, the semaphore count is 0. Now, when eq. one person leaves the toilet, semaphore is increased to 1 (one free key), and given to the next person in the queue.

Officially: "A semaphore restricts the number of simultaneous users of a shared resource up to a maximum number. Threads can request access to the resource (decrementing the semaphore), and can signal that they have finished using the resource (incrementing the semaphore)."
Ref: Symbian Developer Library

Love my job

2007-04-13T18:37:00.000+05:30

Its been pathetic some months (lost ?) I am trying to rediscover myself.... How ? why ? dont know. Every morning I wake up with some day plans ... And the day ends with lots of guilt of not being honest with my job, with my career. Dont know how it is going to be fine. But only know that it will be fine, because history repeats :).

Wondering does this happen with everyone ?

Hah! scorps. were suppose to be very deterministic, am I ?? .......

Just a useless post, because it is meant to be like this.

Live to work or work to Live

2007-01-18T18:13:00.000+05:30

Stumbled onto this nice article

work and life has always been on opposite sides... And each person has to go through it..
I have been thinking about it for a pretty long time.. Do the productivity remain same if we work long hours (this includes asked to work, and work long hours volunterily).. ? I have found from what I call a rich yet small experience of 6 years in the engineering industry....
when we come out of the school, we are overflowing with the education and knowledge (do we?), and we want to do some real good stuff.. thinking that if we put extra hour of work, we can change the world... And over the period this becomes a routine work .. keep aside changing the world. Worst part of this is that you have corrupted your management to think that you like to put up long hours, and if you are not doing that you are not working hard.. and dont get appraised for regular hours .. Pretty sad, eh! But you only set the trend ;)

When I changed my job, I was passionate about the work I do, but I decided not to put up long working hours. And I found that I am better productive in the office as well as in my regular thinking. I can now give a good amount of time to myself, my friends and my family. And I did maintained the same passion for my work.
Ofcourse work is always demanding, but if the time is well planned, it can easily be managed and can be more fun.

recordmydesktop

2007-01-02T12:15:00.000+05:30

Was looking for this tool for quite sometime .... Record your desktop with a video stream.
http://ubuntuforums.org/showthread.php?t=294605

YKK

2006-12-11T20:10:00.000+05:30

Do you know what is "YKK". One of the most day to day used letters ... mostly for men. "YKK" are the letters framed on your zips... Stands for "Yoshida Kogyo Kabushibibaisha", the worlds largest zipper (also called fastners) manufacturer. Next time you zip yourself, you will remember this ;)

blogging

2006-12-08T12:29:00.000+05:30

"Space needs more space in the blog !!! "

Hah, its been around 6 months and 17 posts I started blogging. I am bugged with the kind of space given to me ... ..

When I open my blog on browser or for that matter anybody's blog, I see it occupying just about 50% of the complete page (sidewise), and remaining page is completely blank... When in this world we talk about resource utilization, this much space is a complete waste... I think the blog pages is divided into frames, so I think the frames could be more flexibly made, or atleast some intelligence could be use. It could be customized in the sense that main post could be stretched side-wise to use the blank space. Dont know if this can really be done, and I am just ignorant... Need to find out !!!!!

Can google hear me ?????

performancing

2006-12-07T14:57:00.000+05:30

Well as in last post, I used performancing of firefox. So I just thought of writing down some exeperiences ...
It wasnt upto my marks .... It did removed a couple of words, mostly from the start of the paragraph. Also some of the indentation was badly messed.

I just hope the extensions improve a lots, or I will improve ;)

Btw, if you are a regular visitor of my blog, and if you have a good eye.. you must have noticed that I started putting a lots of links (to the famous pages) ... So the reason is simple... I just want to be noticed by recent but famous verb "google" :). Will write some of my close *but* deep thoughts on page-ranking algo sometime soon.

Kuch Dil ki baatein...

2006-12-07T14:50:00.001+05:30

Ah, its not really about "Dil" ki baatein.. I will do that some other time.. This is something about Heart .. which honestly I flicked from somewhere.. --

This entry comes in blog just for the reason that I should refer to it anytime, anywhere (ofcourse wherever I have internet), and dont lose it.

Btw, I am editing this post through blogging extension of Firefox ie. "Performancing".. Lets see how it goes :D.

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

Heart Diseases, Prevention

Diseases are the major cause of death in today's world, indeed much above any other cause. The prevalence of heart diseases is much more in western countries, some figures showing an incidence of as much as 50%. In India too there has been a considerable rise in the number of heart patients.

How does Heart Function

To understand the diseases of the heart it is essential to understand its structure. Heart can be divided into 4 major parts: left and right auricle that are at the upper part of heart, and left and right ventricle, which constitute the lower part. The auricles are connected to the lung through pulmonary artery and veins. The right part pumps fresh blood to all body parts. The tissues use up oxygen and nutrients from the blood, after which it returns to the left part of the heart. From here, the deoxygenated blood goes to lungs where oxygen mixes in it. The right side again pumps back to the body completing a cycle.

In a normal adult, such cycles happen 72 times a minute. In an active person the rate could be as low as 60 times a minute. Consider the difference: in one day it is 72*60*24 = 103680 versus 60*60*24 = 86400. This means that an active heart is able to pump more blood per cycle.

Heart Diseases

Most of the diseases of the heart are due to formation of deposition in the inner walls of arteries. This prevents smooth flow of blood. Such deposition, like due to excessive intake of calcium especially in childhood, may get rigid with time, more rigid than the artery itself.

In acute cases, an artery may be completely blocked. This happens particularly when a particle flowing in a larger artery block the gate of a thinner artery. This completely cuts off blood flow from some parts, leading to death of tissues.

causes:

Involuntary causes : Age, Hereditary, Gender.

Partially voluntary causes: Diabetes, Obesity, Food habits

Voluntary causes: Smoking, Alcohol, Stress, Inactive Lifestyle

Although the bad effects of inactive lifestyle and unsuitable food start accumulating right from the childhood, their effects may show up after a couple of decades. The risk of heart diseases is much more above the age of 40 and still much more after 60.

There is a strong positive correlation of heart diseases and inheritance.

Females have considerable lesser incidence.

Obesity means that the heart has to work much more, when compared with its strength.

Food habits: The cholestral level above 250 is considered dangerous. A level of 200-225 is also moderately dangerous. Food having saturated fat are especially undesirable: ghee, butter, coconut oil, vanaspati oil, cream, biscuit, egg, meat, fish. Unsaturated fat contained in kardi oil, maize oil and soyabean oil, is less harmful.

Some researchers do not think there is a positive correlation between cholestral level and the amount taken with food. They are of the opinion that the body produces cholestral from other components when it is not taken with food. There have been many experiments where a difference in eating habits did not reflect in the blood cholestral level. The researchers of this school place the blame on homosystine. This is produced from a protein called metheonine when the intake of Vitamin B6 is less. Some experiments seem to confirm this.

A delicate balance of Sodium in blood is essential for proper functioning of heart. Some doctors say common salt, that contains sodium, is not needed at all.

Others say no sugar is needed. The sugar contained in natural food is sufficient for the body.

The role of Exercise in preventing diseases cannot be overemphasized. Doctors say visible effects can be seen just after a couple of weeks of regular exercise. For example, noting down the pulse rate before and after two weeks of regular exercise show up a difference. A stronger heart needs fewer pumps per minute. Even 30 minutes of exercise, with 15 minutes that give moderate stress, also called primary or warm-up zone (like cycling) every couple of days is good enough.

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

Technorati Tags: Heart, Firefox, Performancing,

Thoda sa techy ho jayein.

2006-11-23T20:52:00.000+05:30

Hi,
we have been well versed about process address space (only in understanding terms, and not in depth), but how many times we bothered to figure out how an executable looks like, what all things are there, and in a typical OS how the executable is loaded ??
Well I have been reading about this from various places... wikipedia,google, some C texts etc etc.. and this is what I found .. Just thought to jot down to keep things always into my brain (somebody told me --- YOU WRITE DOWN THINGS, IT WILL ALWAYS BE THERE IN YOUR BRAIN).

In a typical C program text, we have globals, static variables, functions, local variables, and lots of code. When we compile (including linking), we get a.out (Origin of "a.out" name ??? --- assembler and link editor output format, for more info on a.out "RTFM") , and typically it is an ELF (Executable and Linking Format, which was originally "Extensible Linker Format") format file.

So out of the whole program text, executable a.out will have a number of segments --
1. a.out magic string
2. a.out specific contents -- which distiguish machine type, binary type etc.
3. size needed for BSS segment
4. data segment (initialized global and static variables)
5. text segment.

Going bottom up manner,
text segment -- includes executable instructions,
data segment -- has all the Initialized global and static variables.. [Only initialized ones]
Point 3 is important, it is just the size needed for BSS segment [ Block Started by Symbol or to remember -- Better Save Space] ... (and not the BSS segment itself), so the size is equal to total size of all the uninitialized global and static variables and nothing else..
Point 2 and 1 are pretty much executable format specific data.

Question for the reader : Where in executable local variables and function calls stored ... ???

Summarizing uptil this point -
o data segment is completely kept in the object (executable) file
o bss segment isnt kept in the obj file, but only a note of its runtime size requirements.
o the text segment is the most affected part of optimization ... [ Think ...???]
o a.out file size can be affected by compiling for debugging ... [ Analyze ... !!! ]

Now when the a.out file is loaded in the memory, it becomes a process [Old OS text says "Program in the memory is called Process" so I very much support this defn. ;)].. And the space allocated to it is called process address space, and typically it has text, data and code segments only... Lets look at the one to one conversion from executable to process address space -

- text segment (exectuable instruction) -----> as it is ----> text segment (code seg.)
- data segment(initialized global/static data) ----> same--> data segment
- size to bss segment ----> allocate this much size in bss segment (upper/lower part of data segment), and initialize with 0 [thats how all the uninitialized global/static data is initialized to 0.
- a.out specific data ---- > Ignored..

So the remaining part of the process address space is kept as a hole for runtime data, ie. for stack and heap. [ Did you get a clue of the question I asked above ?]

Though this post doesnt look complete, I will stop here for the reader and myself to dive deep into executable data (both on disk and in-memory) ................

However, me open for any discussions ;)

is this a bug in orkut ?

2006-11-21T17:33:00.000+05:30

I suddenly found some spam orkut msgs entered into my scrap book, I thought of deleting them right away, but .... prcastination prevails :).. and I left those dirty messages there itself.
Well today I suddenly found out that those messages are vanised ??? I was surprised, who can do that ... it means somebody in this world has write access (to do something other than writing new msg, or deleting their own msg) also in my orkut scrap book, I can say its not the writer itself because that would be really difficult and next to impossible thing [think why?] ;)......... Now I am worried who all can access/delete/modify/ my details ... .. .
I dont mind spam messages in my scrap book, but I mind giving write authorities to anybody into that.

Pls. ponder

"make" my world.. Just a tip

2006-11-21T12:24:00.000+05:30

Well this article is not what is makefile, what is make and blah blah.. if you are looking for it, I must tell you... go use wikipedia or google

One of the most usable development tool for programming in unix is "make". The rich set of functionalities in make has always amazed me.
Though I used to consider myself pretty much familiar with makefiles, I still could not understand many many advanced makefiles, one of which was to compile hpux kernel, and then linux kernel, well I had mastered (actually understood only) hpux kernel makefile, reading through and getting comfortable to linux kernel makefile is still in my pending items (Procrastination rules :)).. Well I found the following command very handy lately --
"List of suffixes built into make on any machine can be displayed with the following
command"

make -fp - 2>/dev/null < /dev/null Even "make -p" shows the same result, so whats the difference ??

The list of suffixes built into a user makefile mymakefile can be displayed with the following command:

make -fp mymakefile 2>/dev/null

Is there a non-gui alternative to make ?? well, it has to be equally rich in features.

Little bit handy on HPUX

2006-11-17T11:07:00.000+05:30

I always wanted to have one point (url) which gives me a lot of information on hpux. Finally I found some place to breath at (well some of these are pretty much common for normal C programming on Any other Unices also) :-

HPUX Tips

Edgy Eft -- some comments :)

2006-11-12T21:29:00.000+05:30

As I promised... its been a while since I am using this Edgy beta.. Well, here are my observations -

- Upgrading from dapper to edgy was more than a 24 hour pain... , while fresh installation was pretty fast.
- I could finally see the beryl effects on my laptop. In edgy I didnt have to do much as it has compiz installed already..... however, installation on my laptop was a fresh installation, but on my other desktop I couldnt run beryl properly...infact it took a long time to stabilize the machine.... the X server used to go off.
- Boot time is certainly reduced and much visible change.

- Other than these I didnt really see much changes from dapper, for which a person like me will die to move to edgy... I think Dapper still rocks.

More later ...

I love my india

2006-11-10T23:31:00.000+05:30

I dont know whom to credit for this program.. but this one is pretty cool .. just check out the output ... .. you can use CP technology (cut & paste ;)).
Blv. me it is worth taking a look. More importantly once you are tired of appreciating the program, you can really decode the logic also... its very simple :))

#include
void main()
{
int a = 10,b = 10,c = 10;
for (b=c=10;a=
"Love Your Country\
TFy!QJu ROo TNn(ROo)SLq SLq ULo+\
UHs UJq TNn*RPn/QPbEWS_JSWQAIJO^\
NBELPeHBFHT}TnALVlBLO\
FAKFCFQHFOQIAIREET\
MSQGCSQOUHATFAJKSbEALGSkMCSl\
OASn\
^r^r\\tZvYxXy\
T|S~Pn SPm SOn TNn ULo0ULo#ULo-W\
Hq!WFs XDt!" [b+++7]
;)

for(; a-- > 64 ; )
putchar ( ++c=='Z' ? c = c/ 9:33^b&1);

}

The exit !!!

2006-11-02T19:58:00.000+05:30

My random thoughts on what all situations one can face while exiting out from the company ..

Everybody who joins IT company (cant comment on other type of companies), signs some papers on the joining day, which nobody reads .. however those papers contain lots of information which are crucial for anybody's proper existence in the company. Well... actually there is no enough time given to read all those papers and since we are joining the company, we are suppose to be trusting it , and I find this concept very funny :D. Anyways, so one signs a paper which says after the employee becomes permanent, he can leave the company with a notice period of 1 month (in most cases), *but* this notice period can be bought by some certain amount (generally a months basic), and this rule applies to both employee and employer.

Lets assume an employee (Mr. X, who is a permanent emp.) wants to leave, he gives certain notice. In some cases it is 1 month (which is as per papers he signed), and in most cases it is less than a month. In the other case he has an option to pay the money of remaining days, or the company can be liberal enough to let him go happily without taking any money..
BUT what if management says, NO you cant go before 1 month. Do they have such an authority to make Mr. X stay and work for the month, which he wants to do at any cost ???

So what are the options -

- Mr. X stays in the company till his notice period and make the company happy which he is leaving :)

- According to me Mr. X can leave anytime by paying the money to company, as he signed while joining.

My Question is what company can do if Mr. X wants to go early in any case ?? [Did company gets something signed on the papers which Mr. X didnt read while joining]

What if company doesnt relieve the employee ?? .... Some bad relations with company... and company doesnt give relieving letter, or doesnt relieve him formally. And Mr. X leaves the company and joins other company ............ Can there be any issues ???? [ I can think of tons of flaws in this ]

I actually Dont know , these are seem to be more of a loud thoughts ... but ya I am really concerned .... if both the sides (employer and Mr. X) wants to play their bad games (one wants to go, while company do not agree to take money but want him to stay for notice period and work )..... what happens ?
What is more ethical ?
What is a professional approach ?

On the contrary, lets consider a flip side, when Mr Y (another permanent employee) is not performing good, or does some unhappy things with company.. and company decides to FIRE him. Does company consider 1 month notice period so seriously ?? Most of the cases, company just hand over 1 month salary to Mr Y and shows him the door.
So why cant Mr. X do the same thing ????

Can somebody put their thoughts ???

Edgy Eft : will i like it

2006-10-27T10:45:00.000+05:30

The Edgy Eft (ubuntu 6.10) is released. Well more than anything I want to know the philosophy behind this name :).. Look at the release notes for the features in this release ..

Well I am going to try this .. and maybe comment on somethings ;)

Enhancing the skills... The slashdot ways :)

2006-10-26T11:37:00.000+05:30

Since a long time I wanted to ask myself something like this ... Well, lots of other people think like me :), thanks to my regular slashdot reading --

Taking Your Programming Skills to the Next Level?

My Fav.. Ubuntu Tips

2006-10-25T10:30:00.000+05:30

These ubuntu tips which were useful at times for me.... And I dont want to research them in forum.... This is a live post ie.. I will keep updating this ......

READ THIS FIRST prior to posting/upgrading/installing - IMPORTANT links

Sharing a folder in Windows LAN (through SAMBA)

Prince Of Percia for Ubuntu

Making Ubuntu lookalike Mac

The composite Manager Guide- Howto get Vista Effects

Make your own source list

Read/Write to Windows partition (NTFS)

Convert any audio format to mp3

Some Edgy links -

Ubuntu guide for edgy

Complete Source list for edgy

Install beryl/nvidia

Install latest beryl

Cont...

Magical Unix Part-A of Z

2006-09-20T21:46:00.000+05:30

Dont know if there are going to be A to Z versions of Magical Unix.... but it has to start with A only ;)

There was a problem kicked in my mind long ago --
"How can you write a dynamic program ?"
I did solve this problem after lots of thoughts ... today I just thought of preserving it through blogging .. and thus making this blog feel little active ;)

Lets simplify the problem --
The program while compiling should take a C program as the input, compiles that C program, and produces a.out of this new C program ?
Example --

$ gcc
... <--------- waiting for an input which should be a C program .. So I write - main() { printf("hello there\n");} EOF (or Ctrl-D) $ ./a.out hello there $ So how it can be done ??
$ cat dynamic_prog.c
#include "/dev/tty"

$

THATs ALL !!!!! :-) wasnt that a easy task ... How can we explain this -

In unix, current terminal is /dev/tty so when we include this file, the preprosessor tries to include this file, it actually replaces /dev/tty with the current terminal, and so expects an input terminated by EOF (Ctrl-D in unix). And when user enters a C program and as soon as it presses C-d , gcc compiles the C program entered by the user ..... and prepares the
magic a.out ........

Question 1 : How should we achieve the same in Windows ?
Question 2: How should one give beautiful messages on the screen for user to type in a C program... :-) ... like -

$ gcc dynamic.c
Please type a C program here ........ then press C-d to compile that

Well I dont have an answer to this ... Any takers ?

glance in hpux

2006-08-21T16:33:00.001+05:30

A couple of good discussions on usage of glance on hpux.
google-link1

Nice to find memory utilization formula - ((phys.mem - free)/phy.mem) * 100. And the explanation of
having such a high mem utilization on modern OSs in following thread --
"Most modern OSs treat (most of) memory as a cache, so it is
(nearly) full all the time. I.e. why throw away something when it might
be needed in the future? Next question: Why then is "Mem Util" not
close to 100%, but around 90-95%? Answer: HP-UX keeps a little memory
really free, so the response time will be good if some new processes
have to be started. If that was not done, the response time could be bad
if (part of) the "perhaps not (yet) free" memory has to paged out first."
google-link2

Another good explanations on HPUX memory.
google-link3

This one is best...
1. The amount of RAM in use, or resident set size, (RSS).
2. The amount of virtual memory address space, (VSS).
3. The amount of swap space allocated or reserved.

google-link4

google-link5

Week of a programmer.

2006-08-21T16:33:00.000+05:30

Thus spake the master programmer: "After three days without programming, life becomes meaningless."

My addition to it -

"After another two days with programming, life seemed much better earlier" ;)

And yet another weekend approched, and two days without computer.. made me fresh enough to spend another week with two above breaks ;)

How to Survive a Heart Attack !!

2006-08-16T21:24:00.000+05:30

Let's say it's 6.15p m and you're going home (alone of course), after an unusually hard day on the job.
You're really tired, upset and frustrated. Suddenly you start experiencing severe pain in your
chest that starts to adiate out into your arm and up into your jaw. You are only about five miles from the hospital nearest your home. Unfortunately you don't know if you'll be able to make it that far. You have been trained in CPR, but the guy that taught the course did not tell you how to perform it on yourself.

HOW TO SURVIVE A HEART ATTACK WHEN ALONE

Since many people are alone when they suffer a heart attack, without help,the person whose heart is beating improperly and who begins to feel faint, has only about 10 seconds left before losing consciousness.
However,these victims can help themselves by coughing repeatedly and very vigorously. A deep breath should be taken before each cough, and the cough must be deep and prolonged, as when producing sputum from deep inside the chest.

A breath and a cough must be repeated about every two seconds without let-up until help arrives, or until the heart is felt to be beating normally again. Deep breaths get oxygen into the lungs and coughing movements squeeze the heart and keep the blood circulating. The squeezing pressure on the heart also helps it regain normal rhythm. In this way, heart attack victims can get to a hospital.

What is this !!!! " "

2006-06-01T09:29:00.001+05:30

Space !!! A nice, simple and beautiful word .. but it is lot heavy if you think about it.., just like ZERO.
Space - is " "
Space - is an important key in a physical realistic computer keyboard.
Space - is just a blank place
Space - is a complete universe
Space - is something which indicates that something 'was' here..
Space - is used in like --- I want my space

Some different scenerios of its usage, which I can think of right now, well these sentences may have multiple interpretations..
-- Press the 'space' bar to continue...
-- Give me my 'space'
-- I love my 'space'
-- Can I sit in this 'space'
-- space this out
And a lot more ................... space can be filled out... create a space and fill it out :-)

So I am at my space on the web, and I hope u will enjoy reading it to fill the space in your busy time ;)

Please feel free to comment .........