*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).