[9fans] Does 9P provide multicast for files?

[quanstro@quanstro.net (erik quanstrom)]

On Wed Mar 23 16:43:55 EDT 2011, paurea at gmail.com wrote:
> 
> > With 9P, what happens when 2 readers have the same file open, both
> are > blocked on a read() call, and then a writer writes to the file;
> which > of the readers sees the data?  Both?
> 
> Both readers and writers are clients of a 9p file server.  It decides
> who to answer.  It is not specified by the protocol.

excellent answer.

i'd like to add, though, since tags are chosen by the client,
the 9p messages can't be multicast at the transport or
network layer.

so if data becomes available that could unblock both readers
the file server may pick one, neither, or send the same data
(with different tags, etc) to both.

- erik