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From: simon@its63b.ed.ac.uk (Simon Brown)
Newsgroups: comp.arch
Subject: Re: paging in the terminal driver
Message-ID: <705@its63b.ed.ac.uk>
Date: Thu, 29-Oct-87 05:33:53 EST
Article-I.D.: its63b.705
Posted: Thu Oct 29 05:33:53 1987
Date-Received: Wed, 4-Nov-87 04:44:29 EST
References: <573@elxsi.UUCP> <682@its63b.ed.ac.uk> <796@quacky.UUCP> <421@nuchat.UUCP> <3619@sol.ARPA>
Reply-To: simon@its63b.ed.ac.uk (Simon Brown)
Organization: Laboratory for the Foundations of Computer Science, Edinburgh U.
Lines: 36
Keywords: output pagination

In article <3619@sol.ARPA> crowl@cs.rochester.edu (Lawrence Crowl) writes:
>In article <421@nuchat.UUCP> steve@nuchat.UUCP (Steve Nuchia) writes:
>[Is screen paging embedded in the terminal driver good?]
>
>This is easily fixed by sending the program output to a file and then having
>the terminal driver display the file.  This approach provides both paging and 
>long untended output.  The shell could provide this transparently.
>The disadvantages are that one is spending more time doing file i/o, and that
>nearly full file systems will fill up.  These are costs worth paying.

The only way in which this could be done semi-transparently would be for the
shell to redirect output from each command executed into a pseudo-terminal
(a different one for each command), with a master-end acting as a pager.
Unfortunately, it isn't (so far as I know) possible to detect tty-mode changes
over a pty, which means that the paging could *not* be automatically disabled
if the command puts the terminal (ie, the slave end of the pty) into raw or
cbreak mode, which wouldn't be the best at all.
Also, the input would have to go through the pty as well, so that the paging 
could be re-initialized (ie, start a new virtual page) whenever input is 
read - output-only paging is not the way to go!
Of course, this would mean that the file i/o would really be pty i/o, so it
wouldn't be too slow, and the file-system wouldn't be involved - all the
data would stay in the tty buffer space.

A paging streams-module sounds a *much* cleaner way of doing it - pty's just
aren't sophisticated enough.

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