From: Nadav Har'El <1407808@bugs.launchpad.net>
To: qemu-devel@nongnu.org
Subject: [Bug 1407808] Re: virtual console gives strange response to ANSI DSR
Date: Mon, 10 Aug 2020 08:56:41 -0000 [thread overview]
Message-ID: <159704980159.22566.12383430543465802428.malone@chaenomeles.canonical.com> (raw)
In-Reply-To: 20150105215424.22410.18753.malonedeb@gac.canonical.com
The bug still very much exists (I tested qemu 4.2.1):
If you don't use "-serial stdio" (or its newer variants), by default Qemu opens a new black "console" to run the application. It is not clear to me exactly which terminal this console is supposed to emulate, but it does seem to support most ANSI escape sequences I tried. However, it supports the ANSI "DSR" (Device Status Report) escape sequence, ESC [ 6 n (see https://en.wikipedia.org/wiki/ANSI_escape_code), incorrectly, just as I reported in the original issue. This is still true today.
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https://bugs.launchpad.net/bugs/1407808
Title:
virtual console gives strange response to ANSI DSR
Status in QEMU:
Incomplete
Bug description:
With "-serial vc" (which is the default), qemu make strange responses
to the ANSI DSR escape sequence (\033[6n) which can confuse guests.
Terminal emulators supporting the ANSI escape sequences usually
support the "Device Status Report" escape sequence, \033[6n, to which
as a response the terminal injects as input the response \033[n;mR,
containing the current cursor position. An application running in the
guest can use this escape sequence to, for example, figure out the
size of the terminal it is running under, which can be useful as the
guest has no other standard way to figure out a "size" for the serial
port.
Unfortunately, it seems that qemu when run with "-serial vc" (which
appears to be the default), when qemu gets the \033[6n escape sequence
on the serial port, it just responds with a single \033, and that's
it! This can confuse an application, could concievably assume that a
terminal either supports this escape sequence and injects the correct
response (\033[n;mR), or doesn't support it and injects absolutely
nothing as input - but not something in between.
This caused a problem on one shell implementation on OSv that tried to
figure out the terminal's size, and had to work around this unexpected
behavior (see https://github.com/cloudius-
systems/osv/commit/b79223584be40459861d1c12e1cb67e3e49e2a12).
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next prev parent reply other threads:[~2020-08-10 9:10 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-01-05 21:54 [Qemu-devel] [Bug 1407808] [NEW] virtual console gives strange response to ANSI DSR Nadav Har'El
2020-08-07 17:52 ` [Bug 1407808] " Thomas Huth
2020-08-10 8:56 ` Nadav Har'El [this message]
2020-08-12 6:29 ` Thomas Huth
2021-03-22 19:22 ` Peter Maydell
2021-04-30 8:21 ` Thomas Huth
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