Renotify

Renotify is a tool/library to redirect applications which uses inotify. If an application is using inotify to listen for filesystem events on a specific path, Renotify can be used to redirect that path to different path.

Renotify only works on Linux because it specifically targets the inotify Linux kernel subsystem.

Building

Requirements

• D compiler https://dlang.org/download.html. DMD 2.073.0 has been tested

Building

1. Create a new file called config.d in source directory. This file will configure which paths should be redirect and to which file to write log messages to. The config.d file should have content similar to:

   module config;
   
   import renotify.path_map;
   
   // This is the path to the renotify log file.
   // It will be used for debug builds. Optional
   enum logPath = "/path/to/renotify.log";
   
   // This is an array that maps the source paths to the paths which Renotify
   // should redirect to, the target paths. Required
   __gshared immutable pathMaps = [
       // source path            the target path
       PathMap("/home/joe/foo",  "/home/joe/bar"),
       PathMap("/home/joe/foo2", "/home/joe/bar2"),
   ];

2. Execute the build.sh shell script in the root directory of the project. This will produce a file called librenotify.so in the root of the project directory.

The reason why Dub is not used to build the library is that the library needs to be built as a shared library without linking with either Phobos or druntime. Unfortunately this is not supported by Dub.

Running the Tests

Requirements

• Dub https://code.dlang.org/download

Running the Tests

To run the tests invoke dub test from the root directory of the project.

Usage

To use Renotify, start the application that should have its inotify listening redirected with the LD_PRELOAD environment variable with the path to librenotify.so as the value. For example:

LD_PRELOAD=/usr/local/librenotify.so inotifywait -m --format "%e %f" /home/joe/foo

Assuming the configuration used in the first build step, the above command will listen for filesystem events in /home/joe/bar instead of the specified /home/joe/foo

How Renotify Works

Renotify is built as a shared library. This library contains an implementation of the inotify function/system call inotify_add_watch, with the signature:

extern (C) int inotify_add_watch(int fd, const char* pathname, uint mask)

When an application is stared with the LD_PRELOAD=/usr/local/librenotify.so environment variable the inotify_add_watch function implemented in librenotify.so will take precedence of the function implemented by the operating system.

When the application calls the inotify_add_watch function, the implementation in librenotify.so will receive the call. The implementation will look for the passed in pathname in the configured pathMaps. If the given pathname starts with any of the paths in pathMaps it will replace the given pathname with the target found in pathMaps.

It will then call the original implementation of inotify_add_watch with the new pathname using dlsym with the RTLD_NEXT handle.