support/testing/infra/emulator.py: prevent the commands from wrapping
Traditional VT-10x terminals (and their emulators) [0] have a "magic margins" feature that enables the last character position to be updated without scrolling the screen: whenever a character is printed on the last column, the cursor stays over the character, instead of moving to the next line. The Busybox shell, ash, attempts to defeat this feature by printing CR,LF right after echoing a character to the last column.[1] This doesn't play well with emulator.py. The run() method of the Emulator class captures the output of the emulated system and assumes the first line it reads is the echo of the command, and all subsequent lines are the command's output. If the line made by the command + shell prompt is longer than 80 characters, then it is echoed as two or more lines, and all but the first one are mistaken for the command's output. We fix this by telling the emulated system that we are using an ultra-wide terminal with 29999 columns. Larger values would be ignored and replaced by the default, namely 80 columns.[2] [0] https://vt100.net/docs/vt100-ug/chapter3.html - DECAWM [1] https://git.busybox.net/busybox/tree/libbb/lineedit.c?h=1_34_0#n412 [2] https://git.busybox.net/busybox/tree/libbb/xfuncs.c?h=1_34_0#n258 Signed-off-by: Edgar Bonet <bonet@grenoble.cnrs.fr> Reported-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com> Co-authored-by: Yann E. MORIN <yann.morin.1998@free.fr> Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
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@ -101,6 +101,8 @@ class Emulator(object):
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if index != 0:
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raise SystemError("Cannot login")
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self.run("dmesg -n 1")
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# Prevent the shell from wrapping the commands at 80 columns.
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self.run("stty columns 29999")
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# Run the given 'cmd' with a 'timeout' on the target
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# return a tuple (output, exit_code)
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