With the risk of sounding like those /r/programming replies: why would an application be worried about journaling/logs on a file system level? As an application developer all I’m usually told is that the only atomic operations are creates, deletes, and renames. So to update a file you always write a second file and then rename it to the destination.
So
Copy file.txt to file.txt.new Update file.txt.new Rename file.txt to file.txt.old Rename file.txt.new to file.txt.old
This is ”safe” in the sense that in case of a terminated process, the point where it failed can be determined and the application itself can resume or roll back the update on its next run.
What it doesn’t guarantee us that the OS/filesystem provides this rollback independently of the application.
My question is: does Dropbox have any reason to want to work on a lower level than the “normal” high level where you only manually rollback or resume transactions? Do other applications also do this? I always felt that trying to pierce the abstraction of high level FS APIs was unnecessary unless you are writing drivers or file systems.
Some low level programs (antvirus, backups) I can see why they would need to peek under the hood, but to me Dropbox is a pretty dumb file sync program that shouldn’t need complex fs operations like say a backup program. Is it more complex than I give it credit for?