The performance of `FileChannel.transferFrom()` has been improved significantly on Linux kernel version 4.5 and later for the case where the method is used to transfer bytes from one `FileChannel` to another. This change adds to the preexisting set of scenarios in which the number of bytes actually transferred might be less than the number requested to be transferred. That is to say, the value returned by `transferFrom()` can be less than the value of the `count` parameter: a “short transfer.” This is permitted by the specification, but might impact broken code that ignores the returned count and assumes it is always equal to `count`.