How do cloud storage clients (Dropbox, Google Drive) know about changes to the drive?

Question

linux

Actually, the stupid way to do this is to periodically look at the client directory recursively. But don't they use some smarter way --- like some kind of event subscription from the OS (and is there anything like that in Linux?)?

Answer 1

Do you want to understand how cloud storage works or implement similar functionality?
There are subscriptions to change events in the directory - Directory Change Notifications are called.

Answer 2

Dropbox is AWS s3. There is a lambda on which everything is spinning. Google drive is GCP - there are Cloud Functions that work in much the same way)
In general, this is a completely event-based model. List operations are mainly used for cold starts and non-cached directories.