version(5) says:
If the server does not understand the client's version
string, it should respond with an Rversion message (not
Rerror) with the version string the 7 characters
``unknown''.
Pre-lib9p file servers -- all except cwfs(4) -- do return Rerror.
lib9p(2) follows the above spec, although ignoring the next part
concerning comparison after period-stripping. It assumes an
Fcall.version starting with "9P" is correctly formed and returns
the only supported version of the protocol, which seems alright.
This patch brings pre-lib9p servers in accordance with the spec.
maximum file size is 4GB-1 as the file length is stored in
a 32 bit long. make sure it doesnt overflow on write or
or truncate. interpret the file length as unsigned. pass
vlong to readfile()/writefile()/truncfile() so we can
handle overflows and not just ignore the upper bits.
