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Date: Tue, 25 Jul 1995 03:14:55 +1000
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199507241714.DAA25914@godzilla.zeta.org.au>
To: ache@astral.msk.su, bde@zeta.org.au, terry@cs.weber.edu
Subject: Re: dial up at > 9600 baud
Cc: hackers@freebsd.org, harry@hgac.com, jkh@violet.berkeley.edu
Sender: hackers-owner@freebsd.org
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>>The Linux driver has (had?) some optional support to help getty handle
>>this.  After the last close of cuaa, sleeping opens of ttyd return
>>EAGAIN.  This gives getty a chance to send the AT command.

>Does EAGAIN allowed on open by POSIX?

No.  "... opening a terminal device file with the  O_NONBLOCK flag clear
shall cause the process to block until the terminal device is ready and
available.  The CLOCAL flag can also affect open()."  [Opening terminal
device files with O_NONBLOCK set is supposed to always work if the file
permissions allow it.  We probably break this by returning EBUSY for 
some exclusive access and bidirectional cases.]

Bruce