Alsa library musings

I have taken a look at the alsa library tonight.

There seems to be a few fun things one can do. I started to use the small test program: pcm.c from the alsa-lib source directory.

I looked at the code. I have not changed anything yet. But the program is small but shows many aspects of how to interact with pcm streams and drivers.

So one thing I did was to use the small program to create a little scale playing: some thing like:

for a in 1 1.25 1.33 1.5 1.66 1.75 2 do \
    ./pcm -f `echo $a * 440|bc`& pid $! \
    & (sleep 1; kill $pid) \
done

Of course, the numbers 1 1.25 1.33 1.5 1.66 1.75 2 are approximation of some of the notes of a scala. I have been to lazy to look for the exact numbers.

This little test is really not much, and it certainly does make clear how to use the alsa function libraries, but it's fun. Nevertheless, after looking at the code, I have the feeling that I am going to have much fun in the future with playing with sound.

The possibility of combining both my musical theory musings together with my programming is quite a wonderful feeling.

Some of the ideas I have:

• find the different instruments harmonic series and implement a small tool to be able to play some instrument
• implement some composition mechanisms:
  • arpegios
  • Travis picking
  • combinations of instruments
  • combine with language ?

SMP and NUMA architectures

I have had a look at the SMP and NUMA architectures which are for multiprocessor systems.

I found a number of interesting resources:

• OpenMP.org

SMP means symmetric multiprocessor while NUMA stands for Non-Uniform Memory Access. Actually SMP is a type of UMA, i.e Uniform Memory Access. Basically, SMP processor share all the same memory, this imposes some overhead on the cache of the processor to speed up the processing. NUMA architectures (of which different flavor exist, in particular cache-coherent models, aka ccNUMA) have a non uniform access to memory, some processor have access to local caches. In that way, the processes do not need to synchronize to access the data.

Mail Spam Report and Strategies

It is always good to keep an eye on strategies to reduce SPAM. Though this report is a bit old. It presents at least most of the methods to prevent SPAM on one's email address.

Time Managment - Decision Making Techniques

Well... Right now my time management is not so bad as long as I don't have to do anything. But it is still important to remind oneself of the different time management techniques. So I think this blog should be a good way of making sure of this. At least, I will always have this to go back to.

One of the things I always have to keep an eye, it is certainly the decision making process. For this there are few techniques which exist (I looked this up more than once... but the following site should be suitable):

• pareto analysis
• six thinking hats
• grid analysis
• cost-benefit analysis
• decision trees
• force field analysis
• paired comparison analysis
• pmi

I will probably come back to these later.

Kernel Makefile

In this post, I sum up the main Makefile parameters and targets, right now it mainly corresponds to $make help but I might edit this entry to add useful information.

First of all use (if in the directory of the kernel sources)

$ make help

or if you are not in the directory of the kernel sources (then located in )

$ make -C help

This more or less gives the following information.

This outputs a list of possible target and supplementary information:

• a few variable can be set
  ARCH=um ... for the corresponding architecture V=1 > means verbose build V=2 > gives reason for rebuild of target O=dir > is the output directory of the build including .config file C=1 or C=2 > checking (resp force check) of c sources
• Documentation
  • make [htmldocs|mandocs|pdfdocs|psdocs|xmldocs] ->>> build the corresponding docs
• Packages
  • make rpm-pkg > allows to build src and binary rpm packages
  • make binrpm-pkg > allows to build binary rpm packages
  • make deb-pkg > allows to build deb packages
  • make tar-pkg > allows to build uncompressed tarball
  • make targz-pkg > allows to build gzipped compressed tarball
  • make tarbz2-pkg > allows to build bzip2 compressed tarball
• Cleaning targets:
  • clean - Remove most generated files but keep the config and enough build support to build external modules
  • mrproper - Remove all generated files + config + various backup files
  • distclean - mrproper + remove editor backup and patch files
  Note that it can be useful to use ARCH=... in the cleaning process
• Kernel Configuration targets:
  • config - Update current config utilising a line-oriented program
  • menuconfig - Update current config utilising a menu based program
  • xconfig - Update current config utilising a QT based front-end
  • gconfig - Update current config utilising a GTK based front-end
  • oldconfig - Update current config utilising a provided .config as base
  • silentoldconfig - Same as oldconfig, but quietly
  • randconfig - New config with random answer to all options
  • defconfig - New config with default answer to all options
  • allmodconfig - New config selecting modules when possible
  • allyesconfig - New config where all options are accepted with yes
  • allnoconfig - New config where all options are answered with no
• Other useful targets:
  • prepare - Set up for building external modules
  • all - Build all targets marked with [*]
    • * vmlinux - Build the bare kernel
    • * modules - Build all modules
    • modules_install - Install all modules to INSTALL_MOD_PATH (default: /)
  • dir/ - Build all files in dir and below
  • dir/file.[ois] - Build specified target only
  • dir/file.ko - Build module including final link

Note that there are also some little things about tags for editors, but I am not so sure what it really brings.

Linux Standard Base

Yes I like standards... Standards are great... Of course you should not exaggerate it, but yeah standard base are a good thing for linux.

So take a look at the Linux Standard Base ( aka LSB). It is a specification of what rules all linux distribution should respect.

For example, it specifies the executable and linking format: ELF, as well as specifying a number of useful libraries: libc, libm, lipthread, libgcc_s, librt, libcrypt, libpam and libdl. Some util libraries are also specified: libz, libncurses, libutil.

It also specifies a number of commandline command ( see the standard on this subject)

Linux Config Archive

I found an interesting site which is an archive for configuration files from the linux kernel. Unfortunately, it did not work when I tried it. But at least the idea is quite good. I am sure I will try this from time to time.

init scripts

For a few things I am interested in doing, I wanted to be able to have a small script preparing as soon as I boot up. Perhaps it is more interesting to use atd or cron for this but I wanted to make sure how the initscript system works.

So I prepare a small script in order to start some system tools as soon as the boot process is finished.

For example, a little tool starting a remote process when I first boot which would allow me to use some remote processing facilities, e.g (focused) crawler. This could be also some system starting before/after the httpd daemon is up.

For this I took a look at the /etc/init.d/postgres script.

#!/bin/sh # newscript This is the init script for starting up the newscript
# service
#
# chkconfig: - 99 99
# description: Starts and stops the newscript that handles \
# all newscript requests.
# processname: mynewscript
# pidfile: /var/run/mynewscript.pid

# Version 0.1 myname
# Added code to start newscript

Note the use of chkconfig: - 99 99 .

This should be adapted with more useful priorities, basically 99 means that the initscript is started as one of the last scripts. Taking a look at $man chkconfig should prove useful.

The new script stores the pid of the newscript application in /var/run/mynewscript.pid

Note that it also stores things in /var/lock/subsys/

Maintainers File in Kernel and SCM tools for the kernel

I have just had a look at the maintener file in the linux kernel Tree.

I have noticed that there are a number of orphaned project. The question is whether any of these orphaned project really needs to be taken care of.

Another interesting thing was to learn about the different scm and patching tools used in kernel development: git, quilt and hg.

Here is an interesting overview of the reason for the development of git and quilt.

I really start to like the patch approach, and the article linked above gives a good idea of the reasons to use this approach. I should try to summarise in a future post the advantages and disadvantages of the different source code management approaches.

Kernel Stuff

I did some little things with kernel programming (or more compiling) these days.

Part of the things I did were compiling kernel because I wanted to try UML (user mode linux).

So that's what I did:

• Download the kernel configs from: http://uml.nagafix.co.uk/kernels/.
• Download kernels from kernel.org.
• untar the kernels to some directory
• cd into the main directory of the kernel
• copy the config of the kernels into main directory as .config file
• $ make ARCH=um oldconfig
• answered the necessary questions as good as I could
• $ make ARCH=um

  At that point some errors appeared, so I tried to correct them.

• to help me in the debugging process I used $ make V=1 ARCH=um
• when I had some things that did not work well I used the gcc output to call it right away. For example, sometimes the architecture files would not be found right so I used -Iinclude sometimes a precompiler marks was not set correctly so I used -D__someprecompilermarks__. At some point I removed some problematic definition by using this together with a #ifndef in the header file. $ gcc ..... -Iinclude -D__someprecompilermarks__ ...
• then I also downloaded a few kernel repositories using git, though I still need to perfect this.
• I read (or skipped/read) quite a few Documentation files from the kernel or from the internet.
• I familiarised myself with the git web interface, this together with having a kernel RSS feed in my thunderbird.

And all this in one day and half together with other things.

Fedora and chkconfig

I was having some troubles with the starting up of my linux box. Now these problems are solved or at least I hope so :-). The problem seemed to lie with haldaemon or messagebus. After reading a bug description for my problem on bugzilla, I had the solution. (see the bugzilla bug page for bug : 444410). The priorities of some services in runlevel 5 had to be corrected. this can be performed using: $ /sbin/chkconfig --level 5 resetpriorities with being the service's name, e.g NetworkManager, messagebus, ...

Naemi and RPM

As I tend to forget pretty often the syntax of the query format of rpm, I had a short look at the internet. I found this web page which explains some aspects of the use of the rpm -q command.

I discovered a command which I did not know and which might turn out quite useful: namei. It follows the symbolic links until their end point can be found.

Example:

$> namei /usr/java/latest/
f: /usr/java/latest/
d /
d usr
d java
l latest -> /usr/java/jdk1.6.0_03
d /
d usr
d java
d jdk1.6.0_03

AjaxMP - a small Music server

In order to listen to your music on the local network, a php based tool: AjaxMP using mpd as music publishing daemon. Edit

I noticed that the mpd server must be configured in another way if you want to publish it to other nodes in the network.

For this:

1. install mpd
2. set password and port for mpd
3. add music to the mpd directory
4. extract the tar from ajaxmp in a php enabled web server
5. copy config.php.dist to config.php
6. edit the mpd parameters: host, port and password
7. copy user.txt.example to user.txt
8. add for each person needing access a username and a password separated by tabs

The stored password can be stored as md5, and in that way somewhat more secure... But not much!!!

Apache Problem With IP resolution

One of the apache rule for the resolution of API seems to be that addresses of request cannot be numeric.

I commented the rule out... But I should take a look whether there is no better solution.

To find the rule posing the problem I looked at the logs in: /etc/httpd/logs/error_log.

There was a line:

[Fri May 09 02:09:51 2008] [error] [client xxx.xxx.x.xxx] ModSecurity: Access denied with code 400 (phase 2). Pattern match "^[\\\\d\\\\.]+$" at REQUEST_HEADERS:Host. [id "960017"] [msg "Host header is a numeric IP address"] [severity "CRITICAL"] [hostname "xxx.xxx.x.xxx"] [uri "/ajaxmp"] [unique_id "BFUWMX8AAAEAAA8ewlgAAAAC"]

I then did a grep:

$> grep 960017 /etc/httpd/modsecurity.d/*.conf /etc/httpd/modsecurity.d/modsecurity_crs_21_protocol_anomalies.conf:SecRule REQUEST_HEADERS:Host "^[\d\.]+$" "deny,log,auditlog,status:400,msg:'Host header is a numeric IP address', severity:'2',id:'960017'"

I had found the rule causing the problem and commented it out. I hope there is a beeter solution, perhaps a better rule ???