Could we maybe set this up so that it only filters that exact message out? I'm worried that we might silence something useful.

Could we maybe set this up so that it only filters that exact message out?

I tried to figure out how to do this, but I am not nearly enough of a shell magician 😅 As I understand it, we're running in ash in stage-1, so we can't do any fancy Bash process substitution. I guess we could try ... writing to a temp file? Or something with FIFOs? Suggestions appreciated!

@srhb - Okay, I played around with redirection, and I think I have something working. I'm thinking we create two FIFOs, like this little demo:

#!/usr/bin/dash

mkfifo /tmp/zfs-pool-ready.stdout.log.fifo
mkfifo /tmp/zfs-pool-ready.stderr.log.fifo

# In a subshell, redirect all output to the fifo.
(
  exec >/tmp/zfs-pool-ready.stdout.log.fifo 2>/tmp/zfs-pool-ready.stderr.log.fifo

  # Fake ZFS command
  echo "no pools available to import" >&2
  echo "some other error" >&2
  echo "MISSING"
) &

# Print the redirected stderr when filtered
grep -v "no pools available to import" </tmp/zfs-pool-ready.stderr.log.fifo >&2 &
grepJob=$!

# Read the standard input into a variable; this will exit on EOF
state="$(cat /tmp/zfs-pool-ready.stdout.log.fifo)"

# Wait for our stderr forwarder to finish before we continue
wait $grepJob

# Clean up
rm /tmp/zfs-pool-ready.stdout.log.fifo
rm /tmp/zfs-pool-ready.stderr.log.fifo

echo "state: $state"

Thoughts on an approach like this? It's a bit heavyweight, but it does allow us to independently filter stdout/stderr as necessary. I'll test it on a NixOS machine tomorrow, too.

I like it! I don't think it looks terribly heavyweight, and it's very clear to read and extend. I'm wondering if tmp is the right place here, maybe someone else can chime in on that.

I think you don't need the fifo for stdout actually. Or it might be easier to have a fifo for stdout and pipe stderr through grep directly.

Okay, yeah, that makes sense; as long as we're not losing the error that sounds reasonable! I don't have write access, so if everyone is okay with @infinisil's comment, happy to have someone merge this PR as-is 👍

@srhb - Thank you!