valuefs

valuefs

valuefs is a FUSE-based virtual filesystem for numeric values over time.

Syntax

To write values, simply echo numbers to arbitrary filenames within a mounted FS. For example-

$ echo 1 > power_on
$ echo 25.50 > house_temp
$ echo -100 > pending_stuff
$ echo 24.07 > house_temp

The most recent values can be read back, or files removed to clear them. The filesystem only supports numbers - not strings or arbitrary bytes.

Virtual Files

valuefs shines because of its virtual file support. These are read via suffix on a regular file plus a duration query. These are well-documented inside the interface.

• # Average
• % Total
• @ ValueAt
• ^ SafeLatest

For example, if a file house_temp exists, you can request its average over the past 10 minutes by reading this file-

$ cat house_temp#10m
24.785

Similarly, you could request its total over the past ten minutes, or the value it was >10 minutes ago. In the case of functions over the data - e.g., average or total - if there are no values within the time period, the file will not exist.

Each result has a unique inode. The value for a single file (e.g., ac_temp#10m) tends to be cached for a short period of time, but seemingly at most 30s-1m. If you're using valuefs as part of a cron or uploader job, don't read too often.

Logging

For now, valuefs can just dump logs to a flat file.

License

This work is made available under an Apache2 license.