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Mac OS X's FSEvents API has something similar to that. When you create a FSEvent listener you can pass in an old event ID so the system can give you all the stu

Mac OS X's FSEvents API has something similar to that. When you create a FSEvent listener you can pass in an old event ID so the system can give you all the stuff that happened while you weren't listening [1]. Apple uses this for Time Machine (and I suspect Spotlight, too). [1] https://developer.apple.com/library/mac/#documentation/Darwin/Reference/FSEvents_Ref/FSEvents_h/index.html#//apple_ref/c/func/FSEventStreamCreate https://developer.apple.com/library/mac/#documentation/Darwi...

ori_b 15y ago
What happens if a file is created and deleted multiple times? How does this avoid doing a complete walk of FS state and being O(size) itself?
- icehawk 15y ago
  It doesn't. But it does mean you don't have to do it every time This is a nice overview on FSevents http://arstechnica.com/apple/reviews/2007/10/mac-os-x-10-5.ars/7 http://arstechnica.com/apple/reviews/2007/10/mac-os-x-10-5.a...
- Someone 15y ago
  It does not actually tell you what files got changed; it tells you what directories saw at least one change. Programs will still have to inspect those directories to find out what file(s) changed. To quote https://developer.apple.com/library/mac/#documentation/Darwin/Conceptual/FSEvents_ProgGuide/TechnologyOverview/TechnologyOverview.html https://developer.apple.com/library/mac/#documentation/Darwi...: To better understand this technology, you should first understand what it is not. It is not a mechanism for registering for fine-grained notification of filesystem changes. It was not intended for virus checkers or other technologies that need to immediately learn about changes to a file and preempt those changes if needed. [...] The file system events API is also not designed for finding out when a particular file changes. For such purposes, the kqueues mechanism is more appropriate. The file system events API is designed for passively monitoring a large tree of files for changes. The most obvious use for this technology is for backup software. Indeed, the file system events API provides the foundation for Apple’s backup technology. IMO, only telling users what directories changed is a smart move. It means that the amount of data that must be kept around is much smaller. That allows the OS to keep this list around 'forever' (I do not know how 'forever' that actually is)

ori_b 15y ago

What happens if a file is created and deleted multiple times? How does this avoid doing a complete walk of FS state and being O(size) itself?

icehawk 15y ago
It doesn't. But it does mean you don't have to do it every time This is a nice overview on FSevents http://arstechnica.com/apple/reviews/2007/10/mac-os-x-10-5.ars/7 http://arstechnica.com/apple/reviews/2007/10/mac-os-x-10-5.a...
Someone 15y ago
It does not actually tell you what files got changed; it tells you what directories saw at least one change. Programs will still have to inspect those directories to find out what file(s) changed. To quote https://developer.apple.com/library/mac/#documentation/Darwin/Conceptual/FSEvents_ProgGuide/TechnologyOverview/TechnologyOverview.html https://developer.apple.com/library/mac/#documentation/Darwi...: To better understand this technology, you should first understand what it is not. It is not a mechanism for registering for fine-grained notification of filesystem changes. It was not intended for virus checkers or other technologies that need to immediately learn about changes to a file and preempt those changes if needed. [...] The file system events API is also not designed for finding out when a particular file changes. For such purposes, the kqueues mechanism is more appropriate. The file system events API is designed for passively monitoring a large tree of files for changes. The most obvious use for this technology is for backup software. Indeed, the file system events API provides the foundation for Apple’s backup technology. IMO, only telling users what directories changed is a smart move. It means that the amount of data that must be kept around is much smaller. That allows the OS to keep this list around 'forever' (I do not know how 'forever' that actually is)