[Question] [Block] Is there a way to control the read caching of a block device?

[DUO Labs]

*Note: As it turns out, I posted this on the wrong mailing list at first, so 
I'm reposting it here*

I know that the `cache` parameter for `-drive` controls the caching behavior when 
writing from the guest to the host, but is there a way to control the reading 
behavior host->guest? Currently, on HEAD, if I open a file on both the guest 
and host, and write some data to the drive on the (macOS) host, the time until it 
shows up in the (Linux) guest is inconsistent (more specifically, it seems that 
the data won't show up in the guest unless I close the file and reopen it --- by 
contrast, if I write to the drive on the guest, it shows up nearly instantaneously 
on the host).