[Nepomuk] Review Request: Reduce number of watches created by nepomukfilewatch

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This review has been submitted with commit beba672bbf0ee729083b3cb7befea72945d458c8 by Simeon Bird to branch master.

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On Aug. 28, 2012, 5:42 a.m., Simeon Bird wrote:
> 
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> http://git.reviewboard.kde.org/r/106086/
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> (Updated Aug. 28, 2012, 5:42 a.m.)
> 
> 
> Review request for Nepomuk, Vishesh Handa and Sebastian Trueg.
> 
> 
> Description
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> 
> Current master nepomukfilewatcher installs watches on all sub-folders of a watched folder.
> 
> This is problematic:
> 
>  - It means we have to walk the entire directory tree, even for not-indexed folders.
> This is quite a lot of work if you happen to have a large complex directory structure
> mounted over a network in your $HOME (as I do)
> 
> - It means we get inotify watches for directories which are on the filter list; eg, on this computer
> $HOME/build/nepomuk-core/services/filewatch/CMakeFiles/nepomukfilewatch.dir/__/fileindexer
> is watched, causing the filewatcher to go nuts every time I build something.
> 
> - It means we install many more watches than we need to, vastly increasing the probability  
> of hitting the inotify limit.
> 
> This code instead walks the tree until it finds a folder we don't want to index and then STOPS. 
> I couldn't find a way to avoid walking the whole tree with QDirIterator and QDir::Subdirectories, 
> so I use QDirIterator without subdirectories, then create a new QDirIterator for each subfolder to index.
> 
> I can see two objections to this change: 
> 
> 1) If someone moves a file into an ignored directory, they will now presumably lose their metadata. 
> This is true, in my opinion not a big problem; the default configuration is to watch
> $HOME minus temporary build directories. If people are moving files into temporary 
> directories they should probably lose the metadata, and if people manually add directories
> to the ignore list they probably have a good reason and expect nepomuk to ignore them. 
> 
> 2) I changed filterWatch from always returning true to returning true if we want to watch the
> file and false otherwise. I couldn't work out the reason for it always returning true before, 
> so whatever it was, I've probably broken it. 
> 
> Bonus fixes:
> 
>  - Properly pass the return value of addWatch up the tree, so that if we run out of watches, 
> we stop trying to add more.
> 
> - Check for inotify on kernels that have a two-number version string, like 3.0
> 
> - To find the length of event->name, qstrlen was used. If an event is returned 
> for a file outside a watched directory, event->name will not be allocated, and qstrlen 
> may read beyond the end of allocated memory, causing chaos, anarchy and confusion. 
> Use qstrnlen instead.
> 
> Thanks, let me know what you think.
> 
> 
> Diffs
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> 
>   services/filewatch/kinotify.h ab12d66 
>   services/filewatch/kinotify.cpp 4a744d4 
>   services/filewatch/nepomukfilewatch.cpp 9fd5d9c 
> 
> Diff: http://git.reviewboard.kde.org/r/106086/diff/
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> 
> Testing
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> 
> Compiled, run, used for a couple of days, checked which files were actually watched, timed the filewatch service's startup.
> 
> 
> Thanks,
> 
> Simeon Bird
> 
>

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