storagectl's mount.storage helper bundles "open StorageProvider socket
+ Acquire() + dispatch reply + take fd" inline. Future consumers
(systemd-vmspawn boot-time --bind-volume, machinectl bind-volume) need
the same dance.
Factor it into a single libshared helper that takes the Acquire()
parameters by value and returns the fd plus the actual type/read-only
flags. Library code, so no logging — varlink errors are surfaced via
sd_varlink_error_to_errno() and the StorageProvider error_id is
returned to the caller via reterr_error_id (caller decides how to
format messages).
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
Christian Brauner
fad897b8bf