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From: Eric Blake <ebb9@byu.net>
Subject:  Re: Tried out cygwin-inst-20100111.tar.bz2
Date: Wed, 13 Jan 2010 16:04:32 +0000 (UTC)
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Corinna Vinschen <corinna-cygwin <at> cygwin.com> writes:

> 
> IIU the SUSv4 description C, and given that a newly opened console is
> always setup with the default termios settings anyway, we could simply
> set O_TTY_INIT to 0 and be done with it:

Yep, that's my understanding as well.  This link is also informative:

http://www.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap11.html#tag_11_02

"Since the termios structure may include additional members, and the standard 
members may include both standard and non-standard modes, the structure should 
never be initialized directly by the application as this may cause the terminal 
to behave in a non-conforming manner. When opening a terminal device (other 
than a pseudo-terminal) that is not already open in any process, it should be 
opened with the O_TTY_INIT flag before initializing the structure using 
tcgetattr( ) to ensure that any non-standard elements of the termios structure 
are set to values that result in conforming behavior of the terminal interface."

In other words, tcsetattr should always be used on a struct termios obtained 
from a read-modify-write manner, and never from a memset(0) manner, where the 
use of O_TTY_INIT guarantees (trivially, if it is defined to 0) that any 
extension fields in struct termios that need to be set to a non-zero value for 
POSIX conformance are set correctly.

-- 
Eric Blake




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