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coding_in_cdpfgl.md

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Coding into this project

Any help on the project will be very welcomed and appreciated. Have a look at the TODO file, the Roadmap in this file or the @todo notes in the code if you do not know where to begin or what to do. Translations are welcomed ! Please use github's issue system to report any issue or ask to add some feature.

irc

When I'm coding into this project I'm hanging onto #sauvegarde irc channel on oftc servers.

Comments

Sauvegarde uses Javadoc comment style to be parsed by doxygen. Please continue to use this style into comments in the whole project as it will be parsed by doxygen. doxygen has been configured to figure out which parameters are not documented. Please have a look at doxygen output and avoid any warning. If you want the documentation not to include the whole path for files please have a look at cdpfgl.doxygen file and modify STRIP_FROM_PATH variable with your path (where cdpfgl's sources are).

Verifying complexity

I discovered 'lizard' a simple but excellent python program that checks the complexity of a program (ok, how complex it look like because it does not take into account preprocessor macros...). If you plan to hack into this project please look at the result of this program (you may find it following this link: https://github.com/terryyin/lizard)

Learnt things from experiments

  • GFileMonitor in Glib 2.26 does not warn when the file descriptors are exhausted. The default limit on my system is 1024 files monitored
  • inotify interface does warn when one can not add a new watch. It says that the disk is full ! The limit on my system is 8192 watchs at a time.
  • We should use another mechanism to monitor a whole filesystem as limits for GFileMonitor and inotify techniques are very low compared to the number of directories a filesystem might have (my /home have 37826 directories !). We might want to look at redirfs (http://www.redirfs.org/tiki-index.php) or pluginfs (http://www.pluginfs.org/).
  • redirfs, pluginfs and dazuko seems dead (on 02 march 2014). As of 28.03.2015 we can notice that:
  • redirfs has its last commit in Jun 2014
  • pluginfs.org is no more accessible (and all ressources it had). Found plugins on github along with redirfs !!:
  • https://github.com/fhrbata/pluginfs
  • https://github.com/fhrbata/redirfs
  • dazuko still seems dead since 06.09.2008
  • fanotify can not handle file permission changes (chmod and chown) nor file deletion (rm). This is really anoying if one wants restore a directory at a specified time (and we can not decide if a file was deleted at that time).
  • It seems (on my system) that the more the blocksize is small the more the intra-deduplication rate is high (from 2.56 % at 32768 bytes to 8% at 512 bytes). But if the blocksize is smaller then cpu overhead is higher and the maximum filesystem size is smaller... For the default value we will have to find a value that will fit best intra-deduplication rate, cpu demand, maximum filesystem size and low memory consumption. For now the choosen value is 16384 bytes.
  • It seems that it will be difficult to get things via 'simple' message passing between threads -> Use of GAsyncQueue that does all that is needed.
  • I do not feel confortable with msgpack library. I miss documentation. I switched to jansson that is better documented and fills my needs.
  • 0MQ is overkill for my needs. I switched to libcurl and libmicrohttpd.

May be usefull links