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Date:      Sun, 07 Dec 1997 19:50:59 +0900
From:      Kazutaka YOKOTA <yokota@zodiac.mech.utsunomiya-u.ac.jp>
To:        jbryant@unix.tfs.net
Cc:        freebsd-current@freebsd.org, yokota@zodiac.mech.utsunomiya-u.ac.jp
Subject:   Re: sc0 scrollback flaw 
Message-ID:  <199712071051.TAA15489@zodiac.mech.utsunomiya-u.ac.jp>
In-Reply-To: Your message of "Sun, 07 Dec 1997 04:21:57 CST." <199712071021.EAA00984@unix.tfs.net> 
References:  <199712071021.EAA00984@unix.tfs.net> 

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>> >i'm still running the Dec. 2 version of -current, but will be
>> >cvsupping the latest in a few minutes...  i can take a look at
>> >syscons.c, and see if i can find where this is happening...
>> 
>> I did add SC_HISTORY_SIZE stuff to syscons.c. But, I never touched
>> screen clearing part of the code, because SC_HISTORY_SIZE affects the
>> driver only when the history buffer is allocated, which happens a) if
>> the virtual console is opened for the first time, b) if the user runs
>> `kbdcontrol -h lines' to set the history buffer size, c) or if the
>> screen size is changed by `vidcontrol VGA_xxx'.
>> 
>> I'm puzzled.
>
>hmmm...  just remembering, i do change the screen dimensions to 80x60,
>but that is beside the point, as even asfter the switch, i still
>retained the kernel boot messages before, and now everything prior to
>login now is lost...
>
>my .login is enclosed...  btw: i guess i don't do a clear, and the
>mode change does it..  note that clear is commented...  sorry...

Before the introduction of SC_HISTORY_SIZE, syscons didn't check if
the history buffer size is sufficient for the new screen size when the
user is changing the screen size. If you set HISTORY_SIZE to a small
number, say 40 lines, and changed the screen size to 80x60, the system
would crash.

So, syscons was to made to free the history buffer whenever the screen
size is changed and allocate a new buffer.

Ok, probably we should retain the history buffer contents if possible,
when the screen size is changed and when the history buffer size is
changed.

Kazu



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