KFileMon

A picture of a car wreck

A perfectly fine and stable car.

So, after finally getting around to fixing that annoying Plasma Task Manager bug (and I must say, I can’t wait until that applet is ported to to QML, the animation/state change code in there is a mess), I noticed a discussion on IRC about file notification APIs and how there seems to be no good in-kernel solutions at the moment. And after reading Vishesh’ blog post I got an idea for how to maybe solve it using LD_PRELOAD.

The idea is that we have a itsy bitsy library that we inject into every process, by setting LD_PRELOAD in the startkde script. This way the dynamic linker uses our custom functions instead of the normal ones. So when we LD_PRELOAD in a library with a custom rename() function (the standard C library rename() function is used for moving files), it calls our library instead of glibc. Our library in turn tries to connect over a local Unix socket to a central process, and reporting in the old and new filename/path, as well as the current working directory (in case we are working with relative paths). Finally we call the normal glibc rename() function, which does what it does best, actually move the file.

So, I thought why not, and quickly wrote a quick and dirty proof of concept. It is available in git: http://quickgit.kde.org/index.php?p=scratch%2Fsandsmark%2Fkfilemon.git&a=summary

While it might initially seem like a fragile solution, I think it should be pretty reliable in practice (funny pictures aside). It might be crazy enough to actually work. The only thing that won’t work is if applications launched outside of a KDE session move files around, but they have no business moving files around in users home folders anyways (and a solution to this is to set LD_PRELOAD even earlier, for example in /etc/profile.d/ somewhere).

So I thought I’d blog about it, so I can get some useful criticism and learn why it shouldn’t be done this way.

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