terminal_fix_size() queries the terminal for its dimensions with CSI 18
and DSR. On a virtual console that is pointless: the kernel renders the
screen itself, so TIOCGWINSZ is already authoritative.
It is also slow. PID 1 queries /dev/console from console_setup(), and
writes there go through redirected_tty_write(), so while plymouth holds a
TIOCCONS redirect the query never reaches the VT and no reply is ever
generated. Each query then waits out CONSOLE_ANSI_SEQUENCE_TIMEOUT_USEC.
Previously the write failed immediately with EAGAIN — the kernel forces
O_NONBLOCK on /dev/console — so the query was abandoned at no cost; since
ba10d789a8 it is retried until the timeout instead. On a Steam Deck
booting with console=tty1 and plymouth the two queries cost 667ms, about a
quarter of userspace boot time, and no log level shows it because main()
runs console_setup() between log_close() and log_open().
So skip the query on a virtual console and keep the dimensions the kernel
gave us, reporting success rather than an error: declining to ask is not a
failure, and the "dimensions already match" path below returns 0 for the
same reason.
Note this also skips the query on a /dev/ttyN that would have answered,
and does not help a serial console behind a TIOCCONS redirect.
Fixes: ba10d789a8
Fixes: d91a184509
