fbcond blocked indefinitely in open_display_v2() while handing the console
over to the real graphics driver: boot stopped at "fbcond: Performing
handoff" and never reached the "Opened new display" that follows a
successful open.
fbcond is single-threaded and owns the console, so while it waited there it
stopped draining console writers. getty, login and the login shell all
blocked on their writes, which made the failure look like a slow or hung
shell -- the stall point just tracked whichever process next wrote to the
console. If the graphics driver was itself waiting on the console, the two
deadlocked outright and the console never came back.
The wait comes from the scheme-open handshake: inputd signals the handoff as
soon as the driver registers its path, but the driver may not be serving its
scheme yet, and O_NONBLOCK does not bound the open (it governs later reads).
Split the two halves in inputd's ConsumerHandle: display_path_v2() only does
an fpath on our own handle and returns promptly, while open_display_path_v2()
carries the blocking open. fbcond now resolves the path inline and hands the
open to a worker thread, then picks the result up from the event loop via
poll_pending_handoff(). Console output produced meanwhile is buffered in
pending_writes (already the behaviour while the display is unmapped) and
flushed once the new display is mapped.
fbcond now mirrors all framebuffer-console output to the kernel debug (serial)
scheme AND feeds serial input back into the active VT's input queue. Previously,
once fbcond took over the console after display handoff the serial line went
silent (headless operators saw the boot stop at 'Performing handoff' and never
saw the getty login prompt, which draws only to the framebuffer VT). Now the
same console — boot log, login prompt, and shell — is fully usable over serial,
reusing the working framebuffer getty for both surfaces.
Re-adds the archived-but-unapplied scrollback support: a 1000-line ring
buffer in TextScreen capturing all output (incl. pre-handoff boot log), a
Handle::Scrollback variant opened via /scheme/fbcon/<vt>/scrollback, and a
read path returning the retained buffer. Adapted to the current single-step
openat scheme protocol.
Unfortunately the scheme still has to be created by the daemon due to a
kernel bug, but once that is fixed, it would allow delayed spawning of
scheme daemons.
Red Bear OS