ssh is littered with open coded checks of errno after a read or write.
As a matter of good engineering, these should be consolidated into one
routine, try_again(errno).

The current set of checks (which are quite inconsistent) fail to
include all the values of errno that signal that a retry is called for.
For example, EHOSTUNREACH, is an advisory rather than an error.  Currently
ssh will abort a session when TCP/IP is perfectly happy to continue.
Because we want ssh to be robust and reliable, this oversight should
be repaired.

One might argue that if write constantly returns EHOSTUNREACH then we
should quit.  That's reasonable, and it underscores that the current
behaviour is wrong.  It should indeed require many advisories before 
taking such action.