lpsmith / linux-inotify

Haskell binding to inotify.

This is a binding for GHC 7 to the Linux Kernel's inotify interface, which provides notifications to applications regarding file system events, such as file creation, modification, deletion, etc.

linux-inotify was motivated by a recent examination of fsnotify and hinotify, and not being satisfied with the API or implementation details of hinotify in particular.

In contrast to hinotify, which provides similar functionality, linux-inotify is a much thinner binding to the system calls and message format. Some of the advantages are:

1. linux-inotify provides a plain getEvent operator that blocks, instead of implementing a callback API.

2. linux-inotify avoids most of GHC's standard IO handling code, relying on plain system calls with minimal overhead in Haskell-land. (However, it still does make good use of GHC's IO manager via nonblocking inotify sockets and threadWaitRead, so getEvent is still efficient.)

3. linux-inotify does not call forkIO, which means less context switching and scheduling overhead, especially in contexts where hinotify's particular event router isn't a very good fit for your application; e.g. you are implementing a following log file processor.

Some of the downsides are:

1. Due to the use of inotify_init1, linux-inotify currently requires linux 2.6.27 or later, even though inotify support debuted in linux 2.6.13. You can check which version of linux is on a machine via uname -a. I would like to fix this at some point, but it isn't a personal priority.

2. linux-inotify requires GHC 7.0.2 or later, whereas hinotify works with many versions of GHC 6. I have no plans to fix this.

3. linux-inotify is currently just a quick proof of concept. Documentation is missing. The API is still in flux and needs expanding. I've only performed the most preliminary of smoke tests, and I haven't done any performance testing.