The `event_observer` field in the Vmm struct is of type Option<Stdin>.
There are two problems
1. With the way the code is written, it will never be `None`
2. `Stdin` is a singleton, there is no need to store it _anywhere_.

With that in mind, we can just remove this field, and update its two
uses to just directly operate on std::io::stdin(). Since it never
`None', we can also remove the logic that matches and handles the `None`
case. Furthermore, the `Drop` impl used to print the same error message
twice in case resetting stdin to canonical mode failed, so fix that to
only print it once.

Signed-off-by: Patrick Roy <[email protected]>

We always called it right before setup_serial_device(), so just move the
call inside. This will also be helpful once setup_serial_device() can
setup the serial device to print to a file, where we dont need to mess
with stdout in the first place.

Signed-off-by: Patrick Roy <[email protected]>

Have teh aarch64 serial device restoration path use the common serial
device initialization code in setup_serial_device(). The only functional
change here is that now we do set_stdou_nonblocking() on the restore
path, although I would wager that not doing so in the past was actually
an oversight, because we do it for all booted VMs, and for restored VMs
on x86.

Signed-off-by: Patrick Roy <[email protected]>

we only write to it, so no need to pass .read(true).

Signed-off-by: Patrick Roy <[email protected]>

Add a new field, `serial_out_path`, to the logger configuration
(available both via API and CLI) which can be set to the path of a file
into which the output of the guest's serial console should be dumped.

Have the file behave identically to our log file (e.g. it must already
exist, Firecracker does not create it).

If we redirect serial output to a log file, disable serial input via
stdin.

Signed-off-by: Patrick Roy <[email protected]>

Copy the screen log file (which contains firecracker's stdout/guest
dmesg if non-daemonized / no log file specified) to the test_results
directory, to be included in artifacts, instead of explicitly reading
one file and subsequently writing another file in Python code.

Signed-off-by: Patrick Roy <[email protected]>

If SSH to guest is failing, we don't really get much useful in terms of
logs in our ci artifacts. Enable serial console so that we get guest
dmesg always, at least if we have the API server around (which is the
case for the vast majority of tests).

Since serial console is enabled by default now, this means we can stop
explicitly passing modified bootargs in a bunch of tests now.

Disable it for the tests that interact with the serial console via
stdin/stdout (here we are not daemonizing, so we are capturing serial
output anyway).

Disable pylint's "too-many-statements" lint, because it started firing
in microvm.spawn()

Signed-off-by: Patrick Roy <[email protected]>

Add a test that verifies having serial output go to a file works.

Signed-off-by: Patrick Roy <[email protected]>

In test_serial_console_login, we were implementing something that takes
three lines (send and receive data via serial) via an overcomplicated
state machine system. Eliminate the 100 lines of state machine code and
instead just... do the 3 lines of serial.tx/rx.

Signed-off-by: Patrick Roy <[email protected]>

If a test fails, take a snapshot fo the microvms involved, and upload it
as a CI artifact, for post-mortem analysis.

Signed-off-by: Patrick Roy <[email protected]>

These have only caused confusion, as they're output often makes no
sense, and we generally just end up ignoring them (but have discussions
about it every single time). Let's remove them.

Signed-off-by: Patrick Roy <[email protected]>

When A/B-testing, the "A" revision firecracker binary does not know
about the new --serial-out-path CLI argument. Thus, disable the serial
console for all A/B-tests. It gets quite ugly to do for the
vulnerability tests, because the .spawn() call is burried deep in the
fixtures.

This commit should be reverted after merging the PR

Signed-off-by: Patrick Roy <[email protected]>