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Subject: Re: ATRN, connection cacheing (was: ETRN too fast!)
From: Michael Ju. Tokarev (mjttls.msk.ru)
Date: Sat Sep 30 2000 - 20:21:06 CDT

Wietse Venema wrote:
> If someone connects to the SMTP server, authenticates, and sends
> ATRN foo.org, the SMTP server would pass the open connection to a
> session manager daemon, and would trigger the "fast ETRN" feature
> which by now almost works (*). Unless the incoming queue is congested
> by other mail, ETRN or ATRN will cause immediate delivery of mail.

May I ask a little question here?
That is: how smtp server can pass open connection to another process?
I.e. how one unix process can "send" the opened file descriptor to
another process? (If I understand this correctly).

The only way I know of is to create child process that inherit
the fd. Or (and this isn't a "way") by opening another ipc connection
(say, using socket) and staying as a "transport" process that copies
all from it's fd to that new ipc connection and vice versa.
And also probably some unixes have some strange devices for this...