Loss of Console Soft Scrollback
Once in a while I feel as though free/libre software has kicked me in the teeth.
A few months ago I noticed console soft scrollback stopped functioning (
Shift+PgUp/PgDown). This is the console scrollback, outside of any graphical environment, not to be confused with terminal window scrollback.
I noticed this first in my Slackware Current virtual machine (VM). I shrugged, presuming the issue was related to VirtualBox and the continual changes of Current. Then I noticed the same on my Slackware 14.2 systems.
I dug deeper. Apparently the framebuffer soft scrollback feature was removed from newer kernels and backported to supported kernels — as a security patch. The alleged culprit is CVE-2020-14390.
The change would be noticed in Slackware 14.2 by anybody updating from the 4.4.227 to the 4.4.240 kernel. My searching found the regression, oops, “pull request,” was in the 4.4.237 kernel in commit ee3f37702b7e7bfe364f394f18ee8fcc3dd72b77 dated Tue Sep 8 10:56:27 2020 -0700.
Searching the web found the related Linux kernel mail list (LKML) discussions and patches. Reading the LKML finds, “We don’t really have anybody who maintains this code - probably because nobody actually _uses_ it any more.” Well, Linus, horrible conclusion and you forgot to ask users.
The console framebuffer soft scrollback code is just gone. Replaced with — nothing. Linus should know better than to pull functional code without a replacement.
Somebody filed a bug report to reintroduce console scrollback.
Reviewing boot messages no longer is possible unless booting with the
nomodeset boot parameter. Console scrollback is feature I always found useful for reviewing boot messages. Searching the web indicates I am not alone.
This is one of those moments when four letter words are comforting.