Category Archives: Software development

Creating a VM for compiling ZFS with RHEL6.10

As you know I created the DRAID project, based in ZFS.

One of our customers wanted a special custom version for their RHEL6.10 installation with a custom Kernel.

This post describes how to compile and install ZFS 7.x for RHEL6.

First create a VM with RHEL6.10. Myself I used Virtual Box on Ubuntu.

If you need to install a Custom Kernel matching the destination Servers, do it.

Download the source code from ZFS for Linux.

install the following packages which are required by zfs compiler:

sudo yum groupinstall "Development Tools"
sudo yum install autoconf automake libtool wget libtirpc-devel rpm-build
sudo yum install zlib-devel libuuid-devel libattr-devel libblkid-devel libselinux-devel libudev-devel
sudo yum install parted lsscsi ksh openssl-devel elfutils-libelf-develsudo yum install kernel-devel-$(uname -r)

steps to compile the code:1- make sure  the zfs file exists under zfs/contrib/initramfs/scripts/local-top/

if not exists, create a file called zfs  under zfs/contrib/initramfs/scripts/local-top/  and add the following to that file:

#!/bin/sh
PREREQ=”mdadm mdrun multipath”

prereqs()
{
       echo “$PREREQ”
}

case $1 in
# get pre-requisites
prereqs)
       prereqs
       exit 0
       ;;
esac


#
# Helper functions
#
message()
{
       if [ -x /bin/plymouth ] && plymouth –ping; then
               plymouth message –text=”$@”
       else
               echo “$@” >&2
       fi
       return 0
}

udev_settle()
{
       # Wait for udev to be ready, see https://launchpad.net/bugs/85640
       if [ -x /sbin/udevadm ]; then
               /sbin/udevadm settle –timeout=30
       elif [ -x /sbin/udevsettle ]; then
               /sbin/udevsettle –timeout=30
       fi
       return 0
}


activate_vg()
{
       # Sanity checks
       if [ ! -x /sbin/lvm ]; then
               [ “$quiet” != “y” ] && message “lvm is not available”
               return 1
       fi

       # Detect and activate available volume groups
       /sbin/lvm vgscan
       /sbin/lvm vgchange -a y –sysinit
       return $?
}

udev_settle
activate_vg

exit 0

make the created zfs file executable:

chmod +x  zfs/contrib/initramfs/scripts/local-top/zfs

2-  inside  draid-zfs-2019-05-09 folder, execute the following commands:execute Auto generate script:

./autogen.sh

execute configuration script:

./configure

Please note we use this specific configuration for bettter results:

./configure –disable-pyzfs –with-spec=redhat

create rpms:

make rpm

remove all test rpms:

rm zfs-test*.rpm

3- install all created rpms

yum install *x86_64* -y

4- verify that zfs is been installed

zfs

this command will display zfs help. 

Another interesting trick I instructed my Team to do is to add a version number to zfs, with a parameter -v or –version.

So if you want to do the same, you have to edit:

zfs/cmd/zfs/zfs_main.c

Under:

cmdname = argv[1];

In my code is line 7926, then add:

/* DRAIDTEAM - added new command to display zfs version*/
if ((strcmp(cmdname, "-v") == 0) || (strcmp(cmdname, "--version") == 0)) {
    (void) fprintf(stdout, "0.7.0_DRAID-1.2.9.08021755\n");
    return (0);
}

You can check the Kernel Module info by using modinfo zfs, but I found it handy to allow to just do:

zfs -v

A handy trick command line to get the usages of our Python Methods in the code

We all use powerful code analysis tool, but sometimes you’re presented with a problem and you have just… the terminal.

This Bash code is handy.

grep "def " /home/carles/code/gitlab/cloud/terraform/src/scale/lib/iscsi.py | tr "()" "  " | awk '{ print $2; }' |  grep -v "__init" | sort > ./function_names_iscsi.txt

So this basically will get all the methods (“def ” whatever), strip the parenthesis with tr, and get the second column with awk, so basically the method name, sort it and write it to the file.

Then I will cd to the src directory and execute the seconds part:

cd /home/carles/code/gitlab/cloud/terraform/src/
for fname in $(cat ~/function_names_iscsi.txt); do printf "%s: %s\n" "$fname" "$(grep -r $fname *|grep -v 'def ' -c)"; done > ~/functions_being_used.txt

That will produce a nice list with the number of times of the method being called, in the form of:

method_name: occurrences

That’s the equivalent to doing Find Usages is PyCharm.

It’s easy to identify dead code then, with method_name: 0.

You can also run this to your Jenkins to warn when there is Dead Code in your repository.

Google Compute Engine Talk for Group Google Developers Cork

My talk in Google Developers Cork Group.
It’s about deploying an Instance in GCE and grows in complexity until Deploying a Load Balancer with AutoScaling for a group of LAMP Webservers.

Join the group at: https://www.meetup.com/GDG-Cork/

The videos:

Keshan Sodimana: Tensors

Curiosity Python string.strip() removes just more than white spaces

Another Python curiosity.

If you see the Official Python3 documentation for strip(), it says that strip without parameters will return the string without the leading and trailing white spaces.
Optionally you can pass a string with the characters you want to eliminate.

The official documentation for Python 2 says:

string.strip(s[, chars])

Return a copy of the string with leading and trailing characters removed. If chars is omitted or None, whitespace characters are removed. If given and not None, chars must be a string; the characters in the string will be stripped from the both ends of the string this method is called on.

Changed in version 2.2.3: The chars parameter was added. The chars parameter cannot be passed in earlier 2.2 versions.

https://docs.python.org/2/library/string.html

A white space is a white space. Is not an Enter.
But strip() without parameters will remove white spaces (space), and Enter \n and Tabs \t.

Probably you will not realize that unless you read from a file that has empty lines at the end for a reason, and you use strip().

You can see a demonstration following this small program, that runs the same for Python2 and Python3.

And the corresponding output for python2 and python3:

The [ ] characters where added to show that there are no hidden tabs or similar after.

Here I paste the code so you can try yourself:

import sys


def print_bar():
    print("-----------------------------------------------------")


def print_between_brackets(s_test):
    print("[" + s_test + "]")


s_string_with_enters = "  Testing strip not only removing white spaces, but Enter and Tabs s well\n\t\n\n"

print("Testing .strip()")
print("You are running Python " + sys.version)
print("This is the original string")
print_bar()
print_between_brackets(s_string_with_enters)
print_bar()
print("Now after strip()...")
print_bar()
print_between_brackets(s_string_with_enters.strip())
print_bar()
print("As you can see the Enters and the Tabs have been removed, not just the spaced")

I think this should be disambiguate so I decided to take action. Is very easy to blame and never contribute. Not me. I went to Python to fix that and I located a bug reporting this issue:

https://bugs.python.org/issue25433

The issue was registed and made specially interesting contributions by Dimitri Papadopoulos Orfanos.

The thread is really interesting to read. I recommend it.

At a glance:

“Python heavily relies on isspace() to detect “whitespace” characters.”

* Lib/string.py near line 23:
  whitespace = ' \t\n\r\v\f'

So all those characters will be stripped in Python2.7 if you use just string.strip()

The ticket was opened the 2015-10-18 12:15. So it’s a shame the documentation has not been updated yet, more than 3 years later. Those are the kind of things, lack of care, that I can’t understand. Not looking for the excellence.

Please, do note that Python3 supports Unicode natively and things are always a bit different than with Python2 and AscII.

Curiosity Python 2.7 and print() from Python 3.6

I lead a project where I decided to go with Python 2.7, for the wide compatibility across all the Servers around.

With RHEL now supporting Python 3 as well, it doesn’t make much sense any more, as all the major brands do support Python 3 directly.

I saw it coming so in my Coding Style Guide for my Team I explained that we will use print(“”) which is the required way to proceed with Python 3, as opposite to print “whatever” from Python 2. Noye Python 2 supports both methods.

But today something unexpected appeared in the Tests. One line of code was making a print of ().

The line of code was:

print()

And not

print("")

And the curiosity is that if you do print() in Python 2.7 it outputs ().

 

My talk at OpenZFS 2018 about DRAID

This September I was invited to talk in OpenZFS 2018 about DRAID and Cold Storage (Spinning drives).

Thanks to @delphix for all their kindness.

Here you can watch mine and all the presentations.

The slides:


You can download the video of the sample Rebuild with DRAID in here:

draid-rebuild-read-write-1sec-vokoscreen-2018-09-06_11-37-48

Also in the Hackaton I presented my mini utility run_with_timeout.sh to execute a command (zdb, zpool, zfs, or any shell command like ls, “sleep 5; ping google.com”…) with a timeout, and returning a Header with the Error Level and the Error Level itself.

Myself I appear at minute 53:50.

Special greetings to my Amazing Team in Cork, Ireland. :)

Troubleshooting upgrading and loading a ZFS module in RHEL7.4

I illustrate this troubleshooting as it will be useful for some of you.

I requested to one of the members of my Team to compile and to install ZFS 7.9 to some of the Servers loaded with drives, that were running ZFS 7.4 older version.

Those systems were running RHEL7.4.

The compilation and install was fine, however the module was not able to load.

My Team member reported that: when trying to run “modprobe zfs”. It was giving the error:

modprobe: ERROR: could not insert 'zfs': Invalid argument

Also when trying to use a zpool command it gives the error:

Failed to initialize the libzfs library

That was only failing in one of the Servers, but not in the others.

My Engineer ran dmesg and found:

zfs: `' invalid for parameter `metaslab_debug_unload

He though it was a compilation error, but I knew that metaslab_debug_unload is an option parameter that you can set in /etc/zfs.conf

So I ran:

 modprobe -v zfs

And that confirmed my suspicious, so I edited /etc/zfs.conf and commented the parameter and tried again. And it failed.

As I run modprobe -v zfs (verbose) it was returning me the verbose info, and so I saw that it was still trying to load those parameters so I knew it was reading those parameters from some file.
I could have grep all the files in the filesystem looking for the parameter failing in the verbose or find all the files in the system named zfs.conf. To me it looked inefficient as it would be slow and may not bring any result (as I didn’t know how exactly my team member had compiled the code), however I expected to get the result. But what if I found 5 or 7 zfs.conf files?. Slow.
I used strace. It was not installed but the RHEL license was active so I simple did:

 yum install strace

strace is for System Trace and so it records all the System Calls that the programs do.
That’s a pro trick that will accompany you all your career.

So I did strace modprobe zfs

I did not use -v in here cause all the verbose would had been logged as a System Call and made more difficult my search.
I got the output of all the System Calls and I just had to look for which files were being read.

Then I found that zfs.conf under /etc/modprobe.d/zfs.conf
That was the one being read. So I commented the line and tried modprobe zfs and it worked perfectly. :)

 

An Epic fail that are committing all the universities

Article created on: 1528997557 | 2018-06-14 18:32:15 IST

Recently a mentor of the UCC university came to visit me to my office, in order to do the following of one of the members of my Team, an intern.
Conversation was well, and then at some point he asked what courses could do the university teach to their students in order to be more prepared for working with us.
The Head of Business Development, that was in the meeting with me, mentioned something interesting:
– Make the publish their best code in github, bitbucket or similar git repository, and maintain it. It is like a CV.
He pointed that some of the students sent me their repository page, and they have not committed a thing for more than a year. And usually the code that I find there is less than a tic-tac-toe exercise.
– Obviously, to have git experience.
– Having contributed to an Open Source project

I exposed some things that would be helpful to have in the interns and grads that I hire:
– git experience
– Python programming
– C programming
– Unit Testing experience
– Networking experience, in particular iSCSI exports, tcpdump
– Programming Best practices, PEP-8 at least for Python
– Usage of Professional Tools like PyCharm, JetBrains IntelliJ, PHPStorm, Code Lion, Netbeans, Eclipse
– Linux experience. Many of them use Windows at home cause they also play video games. Really few programmers in real life use windows. So at least guys install Virtual Box or VMWare and run Linux in an Virtual Machine.
– Cloud experience. Using instances, CDNs, APIs, tools…

And as the talking advanced I gave him a hint of the Epic fail that all the universities are committing.
They teach git for a semester. They teach Python for one or two semester, the first year usually one, the second year another. And that’s it. Is gone.
When they exit the university they have not programmed in Python for 2 or 3 years, they have not used git, they have not used SQL for the same amount of time, etc…

My boss pointed that the best candidates do side projects in their spare time, and have that bright in their eyes. That sparkling in the eyes is what I call the eye of the tiger, the desire to improve, to learn. That spark.

I told the mentor of my intern that the big mistake is doing things in small parcels, isolated, one block and is gone. That the best way to proceed would be to:
Make the student start a project from the very beginning, from the first semester. Then keep making it bigger and better over time.
Let them improve it over time. Screw it in all the ways possible. Make them reach the limits of their initial architecture. Allow them to face having to redo the thing from the scratch. Allow them to do screw it, to break things, and to learn from their mistakes. Over and over.

Nobody becomes a great programmer coding average things for two semesters.
But let them realize where the problems are. Let them come back to their code of two or three months ago, before holidays, and realize how important is to make comments, to give proper names to the files and to the variables. Let them run that project over so many time, that at some point they have to change computer and they realize that what worked with windows Uppercases and Lowercase mixed files, does not work with Unix (case sensitive).
Let them grow.
Let them see their mistakes over the time.

Let them run the project for so long so they switch several times from Cloud provider, and discover the pros and the cons and the not-to-do, and things like run for your life before using sharing hostings that limit your CPU quota even that kills your MySql instances when they look at the email (true history, connecting to POP3 was raising the CPU and the provider was killing the MySQL instances, and so the queries) or that limits your queries per second, and then ask them to install a drupal and they will learn the hard way why Quality is always better than price and will make the right decisions when they work for somebody else or for their own Startup.

Even many of the supposedly Senior guys never learned from their mistakes, for example the Outsourcing guys, cause they work 6 months to a year in a project and then jump to another. Nobody explains the hell in maintenance and incidental they have left there. Nobody teach them.

Programming an small project for 6 months doesn’t make a master. Doing it for 5 years, growing it, learning from your mistakes and learning the YES and DO-NOT the hard way, the real way that works, cause makes you understand why something is better than other things, is the path.

That also remembers me why I love the MT Notation and many of the guys in Barcelona that saw it criticized the method, while my colleagues at Facebook and Dropbox actually told me that they use it, specially for Python and C/C++.

Allow them to thing about how to solve sorting a list of 1000 items by themselves. Let them think. The lazy will copy, but they will not grow.

Then let them implement a Bubble sort. Let them improve it, if they can. Allow them a week to try to improve that. Then make them sort 1,000,000 items so they see that is bloody slow. How can I improve that?. May I read the data from the drive at once, reading line by line was slow… let them think. Like if they were learning Martial Arts, and so discovering their strengths, that they have fast reflexes, allow them to grow.

Universities have to create good professional, not just machines of passing the exams. Real world demands talent, problem solving abilities, passion, ability to learn, and will to do the things well and to improve, and discipline.

After 5-6 years of programming on a daily basis, with an IDE, git, deploying to the Cloud as the basic, and growing a program and seeing the downsides of the solutions chosen, observing that the caveats where for a reason, learning that the Hardware is important, that is not the same to write to memory that to disk or to network, detecting the problems, redoing things, ending in a cul-de-sac, fixing, improving, learning, growing the project, growing himself/herself as a mind, as a programmer, as a thinker, as an expert, daily, even if it’s 30 minutes per day, then that person is prepared for some serious business.

Like piano, guitar, painting, writing… and any other activity, one require continue training in order to improve.

Students have to follow a journey in order to improve.

Let them start with Command Line, i.e. in C and files. Let’s do add later database support.

Deal with buffer overflow, file descriptor, locks and conversion types. Let them migrate to another language the entire project, using Git from the beginning.

Let them migrate again when they need to add Web support. Allow them to discover that instead of reloading all the page they can use Ajax/JSON. Let them deal with click-click that many common users do on the page buttons (so they submit twice the information). To discover SQL Injections. To use a Web Framework. To add Unit Testing. Add some improvement via Javascript Frameworks like responsive for mobiles.

Allow them to use a new Database, new Webserver or technology that is fashion and everybody on Twitter talks about, so it crashes in their face. And so they discover that they will not play or discover new technologies in actual project time in the Company of their future employers, cause shit happens, and impacts the Schedule, and the Company loses money. Universities: Teach them, let the students learn this for themselves, rather than screwing it up in several companies after university.

A simple sample to print colors in Terminal with Python (local tty or stty in a ssh)

This is a very simple code, but handy.

I love the output for the simplicity and I use to check for my programs to see what will suit best.

 

#!/bin/env python 
# Collection of Effects
# 1m - Bold
# 2m - Normal Dark colors
# 3m - Italic
# 4m - Underline
# 7m - Background
# 9m - Strikethrough (except 38;9m)
# 40m - Bakground Dark Grey, with the colors in foreground 1 (bold),2,31-37
# 41m - Bakground Red, with the colors in foreground 1 (bold),2,30-37
# 42m - Bakground Green, with the colors in foreground 1 (bold),2,30-37
# 43m - Bakground Yellow, with the colors in foreground 1 (bold),2,30-37
# 44m - Bakground Blue, with the colors in foreground 1 (bold),2,30-37
# 45m - Bakground Violet, with the colors in foreground 1 (bold),2,30-37
# 46m - Bakground Cyan, with the colors in foreground 1 (bold),2,30-37
# 47m - Bakground Grey, with the colors in foreground 1 (bold),2,31-37
# 49m - Normal

CLEAR = "\x1B[0m"

a_s_background = ["1", "2", "3", "4", "7", "9", "40", "41", "42", "43", "44", "45", "46", "47", "49"]
a_s_color = ["1", "2", "31", "32", "33", "34", "35", "36", "37"]

for s_effect in a_s_background:
    s_line = ""
    for s_color in a_s_color:
        s_color_text = "\x1B[" + s_color + ";" + s_effect + "m"
        s_line += s_color_text + s_color + ";" + s_effect + "m" + CLEAR + " "
    print(s_line)
    print("--------------------------------------------")

You can find the source code here:

https://gitlab.com/carles.mateo/blog.carlesmateo.com-source-code/-/blob/master/colors_in_terminal.py

Please, take in count that the colors may be different depending on the Terminal used, so if you’re creating a commercial application I recommend you to try with some of them like: ubuntu terminal, ssh, putty for windows, MobaXTerm…

 

View from the colors from the Console of PyCharm Community Edition

A sample way to return in Python not-to-do

Today I was checking the code, the latest push to the git repo, as I always do, and I saw something that was wrong.

Often Engineers can be confused by the ways different languages treat similar operations, so similarly as POSIX I try to use an standard way to program in any language that makes the code very clear and easy to understand, no matter if it’s C, Java, Python, PHP…

My code and the code of my Teams will be clear, and easy to understand. And as the good Engineers jump from language to language upon the needs, is better for all to proceed like this to avoid confusions.

In this case I want to cover a simple case that I detected. A wrong usage.

The code was returning True on success and if not simply return.

Here I show a simple demonstration that return itself will be returning return None.

# Proof of Concept for avoiding return without the type
# Author: Carles Mateo
# Creation Date: 2018-03-27
#

from pprint import pprint

def boolean_test(b_value):
if b_value is False:
return

return True

b_true = boolean_test(True)
b_false = boolean_test(False)

pprint(b_true)
pprint(b_false)

if b_false is False:
print “I detect it as False (even if it’s None)”

if b_false is True:
print “I detect it as True (even if it’s None)”

if b_false is None:
print “It is None!”

print “Be careful”

Variables use the MT Notation. I include tips like this and guidelines in programming guide for my Teams.

See: Wiki Python Programming/Data Types