Re: [Qemu-devel] [PATCH 2/3] move vm stop/start to migrate_set_state

[Avi Kivity]

On 07/12/2009 06:31 AM, Anthony Liguori wrote:
> Jamie Lokier wrote:
> > If you get an error during the last write(), I wouldn't trust that to
> > mean the recipient will definitely not see the data you wrote.  (Enjoy
> > the double negative).  It's another variation of the handshake
> > uncertainty, this time reflected in what write() should report when
> > it's uncertain about a network transmission.  If it reports an error
> > when it's uncertain, then you can't trust that a write() error means
> > the data was not written, only that a problem was detected.
>
> I think you're stretching here.  If it really were the case that 
> write() could actually result in data being sent out the wire and yet 
> still returning an error, it would make all error handling in Unix 
> unmanagable.  I can't believe this is possible in Linux and without an 
> actual counter-example, I'm inclined to believe the same is true for 
> every other OS out there.

It's actually a common scenario for block devices.  I don't know about 
networking, but for disks a write can be completed and then report an 
error if the cable or power was disconnected before the acknowledge 
could arrive.

It could conceivably happen with networking if the device reports an 
error when it isn't sure if the data was sent out or not (but it 
actually was), or if some path after the transmission required a memory 
allocation, which failed.

--
error compiling committee.c: too many arguments to function