cross-device copying / USB improvements

[Simon 'corecode' Schubert]

Matthew Dillon wrote:
:- would return errors to the waiting processes after the timeout
:
:This would be a cool way to "recover" from accidently interrupted
:connections or unreliable devices.
    Yah, but I don't think it is in the cards.  There is no way
    for the kernel to know what buffers actually made it to the
    device or not.
If the disk layer ack'ed the block, it should be on stable storage, 
right?  Otherwise it isn't.  To me that would mean that we just have to 
write out all blocks in flight (those with errors) and the ones we 
didn't even write yet.  Of course that's only true for non-caching 
media, but what can you do.

cheers
  simon