cyberz.org http://www.cyberz.org/blog Andrea Leofreddi's homepage Thu, 04 Mar 2010 21:10:58 +0000 http://wordpress.org/?v=2.9-rare en hourly 1 SVGPan: a Javascript SVG (Viewer) Pan/Zoom/Drag library http://www.cyberz.org/blog/2009/12/08/svgpan-a-javascript-svg-panzoomdrag-library/ http://www.cyberz.org/blog/2009/12/08/svgpan-a-javascript-svg-panzoomdrag-library/#comments Tue, 08 Dec 2009 18:37:34 +0000 andrea http://www.cyberz.org/blog/?p=96 Some time ago the need for a browser-compatible vectorial language pushed me to consider the SVG markup language (I won’t say anything about Internet Explorer – it’s just unsupported there). The language itself is great, but, as a beginner, I was so disappointed about the fact that on the Internet I couldn’t find ANY library ready to use for panning and zooming features that I had to write one from scratch.

The SVGPan library features:

  1. Panning (pan à la Google maps) (click on the white background and pan)
  2. Zooming (using the mouse wheel)
  3. Element dragging (click on a drawing element and drag it somewhere else)
  4. Combinations of the above like zooming while dragging

The resulting javascript library is published here, in the hope that someone can find it useful. The library itself is very small and easy to use; and it’s licensed under the BSD license. You can try a demo here

View code
Title: SVGPan demo
Description: Hello

You can also open the demo in a new page and download the SVGPan library here.

The library itself requires a root group to be identified by the id viewport, which confines the SVGPan library effects, and the import of the javascript code as well. For example, to adapt the tiger drawing, was necessary to add the following:

<script xlink:href="SVGPan.js"/>
<g id="viewport" transform="translate(200,200)">...

You may also try another SVG example (triple integral, from Wikipedia).

Zeng Xiaohui has provided a patch to support the mouse wheel on Safari/Chrome, which has been merged into the latest version of SVGPan.

]]> http://www.cyberz.org/blog/2009/12/08/svgpan-a-javascript-svg-panzoomdrag-library/feed/ 8 Bode and Nyquist diagrams using GNU Octave http://www.cyberz.org/blog/2009/12/07/bode-and-nyquist-diagrams-using-gnu-octave/ http://www.cyberz.org/blog/2009/12/07/bode-and-nyquist-diagrams-using-gnu-octave/#comments Mon, 07 Dec 2009 17:51:36 +0000 andrea http://www.cyberz.org/blog/?p=14 Using GNU Octave is easy to plot Bode and Nyquist diagrams, as follows:

bode(zp([], [-1*i, i, -1], 1))

nyquist(zp([-0.5], [0.0, -0.2, -4], 1))

]]> http://www.cyberz.org/blog/2009/12/07/bode-and-nyquist-diagrams-using-gnu-octave/feed/ 0 Bacula mail changer script (aka poor man’s autoloader) http://www.cyberz.org/blog/2009/06/08/bacula-mail-changer-script-aka-poor-mans-autoloader/ http://www.cyberz.org/blog/2009/06/08/bacula-mail-changer-script-aka-poor-mans-autoloader/#comments Mon, 08 Jun 2009 22:16:32 +0000 andrea http://www.cyberz.org/blog/?p=24 I enjoy Bacula for automated home backups on DLT and DDS tape drives. Being used at home there’s no – obviously – big-dollar-company-manager to ask for an autoloader; and when the time of a tape change comes bacula lacks a simple way to request a manual tape change and just hangs up. So I managed to build a fake autoloader shell script, which, using emails, would emulate a real autoloader. This script, which I baptised mail-changer, features:

  • email support
  • periodic email resend when tape change is needed
  • tape detection and check (if you’re supposed to insert tape 4 and you enter 5, the script will kindly refuse the tape, unload it and send a warning email message asking for the right one)

To implement the third point (tape detection and check), it was necessary to extract the tape id from the bacula tape. That can be done looking at the bacula’s tape header structure:

The first structure stored is called “Block Header” and is 24 bytes long:

   uint32_t CheckSum;                /* Block check sum */
   uint32_t BlockSize;               /* Block byte size including the header */
   uint32_t BlockNumber;             /* Block number */
   char ID[4] = "BB02";              /* Identification and block level */
   uint32_t VolSessionId;            /* Session Id for Job */
   uint32_t VolSessionTime;          /* Session Time for Job */

Then a “Record Header” follows (12 bytes):

  int32_t FileIndex;   /* File index supplied by File daemon */
  int32_t Stream;      /* Stream number supplied by File daemon */
  uint32_t DataSize;   /* size of following data record in bytes */

Then a structure which is interesting for us, called “Volume Label” follows:

  char Id[32];              /* Bacula 1.0 Immortal\n */
  uint32_t VerNum;          /* Label version number */
  /* VerNum 11 and greater Bacula 1.27 and later */
  btime_t   label_btime;    /* Time/date tape labeled */
  btime_t   write_btime;    /* Time/date tape first written */
  /* The following are 0 in VerNum 11 and greater */
  float64_t write_date;     /* Date this label written */
  float64_t write_time;     /* Time this label written */
  char VolName[128];        /* Volume name */
  char PrevVolName[128];    /* Previous Volume Name */
  char PoolName[128];       /* Pool name */
  char PoolType[128];       /* Pool type */
  char MediaType[128];      /* Type of this media */
  char HostName[128];       /* Host name of writing computer */
  char LabelProg[32];       /* Label program name */
  char ProgVersion[32];     /* Program version */
  char ProgDate[32];        /* Program build date/time */

What is really important for us is the VolName field, which is at relative offset +56 from the beginning of the Volume Label. Adding 12 bytes of Record Header and 24 of Block Header makes 92 bytes.

Please note that mail-changer has been developed on Solaris 10 using CSW’s Bacula, you may need to work a bit to adapt it to your unix.

You can download mail-changer here.

]]> http://www.cyberz.org/blog/2009/06/08/bacula-mail-changer-script-aka-poor-mans-autoloader/feed/ 0 Some applications using I2C http://www.cyberz.org/blog/2009/06/08/some-applications-using-i2c/ http://www.cyberz.org/blog/2009/06/08/some-applications-using-i2c/#comments Mon, 08 Jun 2009 21:49:43 +0000 andrea http://www.cyberz.org/blog/?p=64 Parallel and serial ports are disappearing from today’s pc making life harder for the people who wants to connect their home-made devices to a pc. The USB bus seems to be very appealing but it has the drawback of complexity while the I2C bus is very easy to implement and it’s widely supported by many devices, with the drawback of no direct pc connection (to be honest it’s used inside the pc, so somewhere on the motherboard there is a i2c bus, but yet I haven’t found any decent connection to the external world to use it – no, i won’t solder things on memory modules). Since the first way to start experimenting with i2c is building an i2c port, I’ve built a parport-to-i2c interface implementing the i2c schematics made by Kosma Moczek with the idea of replacing it with a more modern USB-to-I2C solution in the future.

So here it is the prototype of the parport to i2c interface:

The i2c board

To test the interface bus, some i2c device was needed. A common 24c04 eeprom was very easy to find, so I just setup some wires to have the 24c04 connect the bus (note the power cord powers up the parport board too). That is the result:

The 24c04 eeprom

Using the i2cdetect from lmsensors with the 24c04 unplugged, I was able to scan the i2c bus without results as expected:

[root@thufir ~]# i2cdetect -a 3
WARNING! This program can confuse your I2C bus, cause data loss and worse!
I will probe file /dev/i2c-3.
I will probe address range 0x00-0x7f.
Continue? [Y/n] y
0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
[root@thufir ~]#

Plugging the 24c04 eeprom in the i2c bus, a probe finds out something:

[root@thufir ~]# i2cdetect -a 3
WARNING! This program can confuse your I2C bus, cause data loss and worse!
I will probe file /dev/i2c-3.
I will probe address range 0x00-0x7f.
Continue? [Y/n] y
0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: 50 51 -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
[root@thufir ~]#

The eeprom has been found at 0×50-1 address, which is as expected (the 24c04 has the ‘1010 E2 E1 A8′ address scheme, so in my case E2 and E1 were ground producing 1010000 and 1010001).

To be sure about the functionality of the port, I used the eeprog program by Stefano Barbato to test the 24c04.

Writing “hello world\n” on the first 12 bytes of the eeprom was fine:

[root@thufir eeprog-0.7.6]# echo hello world | ./eeprog -f /dev/i2c-3 0x50 -w 0:12
eeprog 0.7.6, a 24Cxx EEPROM reader/writer
Copyright (c) 2003-2004 by Stefano Barbato - All rights reserved.
Bus: /dev/i2c-3, Address: 0x50, Mode: 8bit
Writing stdin starting at address 0x0
............

…and so was reading what’s inside the first 12 bytes of the eeprom (the “hello world\n” string which we have just written).


[root@thufir eeprog-0.7.6]# ./eeprog -f /dev/i2c-3 0x50 -r 0:12
eeprog 0.7.6, a 24Cxx EEPROM reader/writer
Copyright (c) 2003-2004 by Stefano Barbato - All rights reserved.
Bus: /dev/i2c-3, Address: 0x50, Mode: 8bit
Reading 12 bytes from 0x0
hello world
[root@thufir eeprog-0.7.6]#

The i2c eeprom is working as expected. The eeprom was connected with a 3 meters cable. As of today I still have to buy some PCF8574 to start experimenting with some other circuits.

]]> http://www.cyberz.org/blog/2009/06/08/some-applications-using-i2c/feed/ 2 Code Review http://www.cyberz.org/blog/2009/02/18/code-review/ http://www.cyberz.org/blog/2009/02/18/code-review/#comments Wed, 18 Feb 2009 18:34:45 +0000 andrea http://www.cyberz.org/blog/?p=55 qa

]]> http://www.cyberz.org/blog/2009/02/18/code-review/feed/ 0 Nagios nrpe and sudo: “NRPE: Unable to read output” http://www.cyberz.org/blog/2009/01/03/nagios-nrpe-and-sudo-nrpe-unable-to-read-output/ http://www.cyberz.org/blog/2009/01/03/nagios-nrpe-and-sudo-nrpe-unable-to-read-output/#comments Sat, 03 Jan 2009 18:21:21 +0000 andrea http://www.cyberz.org/blog/?p=49 On CentOS 5 (and RedHat EL as well), you can encounter the following behaviour when configuring an nrpe plugin with sudo:

[andrea@feyd ~]$ /usr/lib/nagios/plugins/check_nrpe -H 1.2.3.4 -c check_md_raid
NRPE: Unable to read output


Given that check_md_raid is defined as follows, in nrpe.conf:

command[check_md_raid]=sudo /usr/local/bin/nagios_check_md_raid

And given (for completeness) its relative /etc/sudoers line as follows:

nagios ALL=(ALL) NOPASSWD:/usr/local/bin/nagios_check_md_raid

Then the problem is in the requiretty options in /etc/sudoers, enabled by default on CentOS. Simply comment it as follows:

#Defaults requiretty

After that the plugin should work as expected:

[andrea@feyd ~]$ /usr/lib/nagios/plugins/check_nrpe -H 1.2.3.4 -c check_md_raid
RAID OK: All arrays OK [1 array checked]

]]> http://www.cyberz.org/blog/2009/01/03/nagios-nrpe-and-sudo-nrpe-unable-to-read-output/feed/ 4 Using samba with autofs on Fedora 9 http://www.cyberz.org/blog/2008/09/07/using-samba-with-autofs-on-fedora-9/ http://www.cyberz.org/blog/2008/09/07/using-samba-with-autofs-on-fedora-9/#comments Sun, 07 Sep 2008 14:55:54 +0000 andrea http://www.cyberz.org/blog/?p=26 Mount a samba share on the fly without having it mounted statically at boot via the /etc/fstab file can bring you the advantage of an unpainful boot in case of unavailability of the samba server like in the following common scenarios:

  • laptop: you mount your pc share at home, but when you move it becomes unavailable
  • workstation: you mount the share of your workmate – but when he/she goes on holiday his/her workstation stays off

Using autofs this can be accomplished easily following these steps:

  1. Set /auto under the control of autofs adding this line to /etc/auto.master:

    /auto            /etc/auto.auto    --timeout=5 --ghost

  2. Point directory to a samba share //server/share in /etc/auto.auto:

    directory -fstype=cifs,credentials=/etc/smb.auth ://server/share (directory is a child directory of /auto)

  3. Store access credentials to the samba share in /etc/smb.auth:

    username=yourusername
    password=youpassword

  4. Secure the password file:

    # chmod 600 /etc/smb.auth

  5. Start autofs:

    # /etc/init.d/autofs start
    Starting automount: [ OK ]

]]> http://www.cyberz.org/blog/2008/09/07/using-samba-with-autofs-on-fedora-9/feed/ 0 Bash delirium (delirio in bash) http://www.cyberz.org/blog/2008/04/18/delirii-in-bash/ http://www.cyberz.org/blog/2008/04/18/delirii-in-bash/#comments Fri, 18 Apr 2008 12:19:44 +0000 andrea http://www.cyberz.org/blog/?p=19 f1() { :; }; f0() { f$((${#1}==0)) "${1:1}"; echo -n "${1:0:1}"; }; f0 'dlrow olleh'; echo

]]> http://www.cyberz.org/blog/2008/04/18/delirii-in-bash/feed/ 3 MusicBrainz not working with Amarok on Fedora 8 http://www.cyberz.org/blog/2008/04/13/musicbrainz-not-working-with-amarok-on-fedora-8/ http://www.cyberz.org/blog/2008/04/13/musicbrainz-not-working-with-amarok-on-fedora-8/#comments Sun, 13 Apr 2008 10:14:05 +0000 andrea http://www.cyberz.org/blog/2008/04/13/musicbrainz-not-working-with-amarok-on-fedora-8/ On my Fedora 8 system with Amarok I was trying to fill an mp3’s tag header using MusicBrainz, getting the following error:

Tunepimp (MusicBrainz tagging library) returned the following error: "Fingerprinting of .mp3 files is not supported."

To make it work, just yum install libtunepimp-extras-nonfree

]]> http://www.cyberz.org/blog/2008/04/13/musicbrainz-not-working-with-amarok-on-fedora-8/feed/ 0 SSH X11 forwarding issue http://www.cyberz.org/blog/2008/04/12/ssh-x11-forwarding-issue/ http://www.cyberz.org/blog/2008/04/12/ssh-x11-forwarding-issue/#comments Sat, 12 Apr 2008 21:38:53 +0000 andrea http://www.cyberz.org/blog/2008/04/12/ssh-x11-forwarding-issue/ Recently I’ve been in an awkward situation with ssh and X11 forwarding, where ssh using the classic -Y (or -X) switch wasn’t working (DISPLAY was not set):

[andrea@duncan ~]$ ssh -Y root@vladimir
root@vladimir's password:
Last login: Sat Apr 12 23:30:09 2008 from ***
[root@vladimir ~]# echo $DISPLAY
[root@vladimir ~]#

If you are experiencing the same and your sshd_config looks fine (which means TCP and X11 forwarding is already enabled) then the answer is missing xauth!

On RedHat yum install xauth will do the trick

]]> http://www.cyberz.org/blog/2008/04/12/ssh-x11-forwarding-issue/feed/ 0