Is there a way to sync a specific device in Linux?
This would be used to ensure that, e.g., writes to a USB thumb drive have taken place without waiting for queued writes from a video processing job to complete on an unrelated RAID array.
If there is a system call / combination of parameters that can achieve this, I could probably write a simple C wrapper. If someone knows of a Ubuntu package that can do this, that'd be even better.
You cannot sync(2) a device, and that does not have any sense. You are syncing a file system (not the device mounting it) with syncfs or the entire page cache with sync.
The sync(2) syscall is called by the sync(1) command.
(I don't know of any usual command doing a syncfs)
However, you could flush the buffers for a file system by using the Linux specific syncfs(2) syscall. So write a simple C wrapper doing that.
For an opened file descriptor, you could use fsync(2) or fdatasync
Notice that unmounting a file system is generally flushing it.
Consider using Direct I/O, this will avoid the need to sync. Some filesystems can be forced to use it via mount option (dio).
