cmd/earlyinit: mount system device

This currently relies on a trusted bootloader to determine the boot device.

Signed-off-by: Ophestra <cat@gensokyo.uk>

cmd/earlyinit/uevent.go

@@ -0,0 +1,103 @@
+package main
+
+import (
+	"context"
+	"log"
+	"time"
+
+	"hakurei.app/fhs"
+	"hakurei.app/internal/report"
+	"hakurei.app/internal/uevent"
+)
+
+// newRejectColdboot returns a function to be called on every subsequent pending
+// coldboot, and returns whether coldboot should proceed. Rejection is sticky.
+func newRejectColdboot() func() bool {
+	// one coldboot per five minutes, two consecutive coldboot
+	const (
+		coldbootInterval = 5 * time.Minute
+		coldbootBurst    = 2
+	)
+
+	done := make(chan struct{})
+	s := make(chan struct{}, coldbootBurst)
+	s <- struct{}{} // for early fault before reporting is ready
+	go func() {
+		t := time.NewTicker(coldbootInterval)
+		for {
+			select {
+			case <-done:
+				return
+
+			case <-t.C:
+				select {
+				case s <- struct{}{}:
+				default:
+				}
+			}
+		}
+	}()
+
+	return func() bool {
+		select {
+		case <-s:
+			return true
+
+		case <-done:
+			return false
+
+		default:
+			close(done)
+			return false
+		}
+	}
+}
+
+// consume continuously consumes events from conn with retries.
+func consume(
+	ctx context.Context,
+	r *report.Reporter,
+	conn *uevent.Conn,
+	uuid uevent.UUID,
+	events chan<- *uevent.Message,
+) {
+	defer close(events)
+
+	nextColdboot := newRejectColdboot()
+	coldboot := true
+retry:
+	if dispatchErr := conn.Consume(ctx, fhs.Sys, &uuid, events, coldboot, func(path string) {
+		log.Println("coldboot visited", path)
+	}, func(err error) bool {
+		if _, ok := err.(uevent.NeedsColdboot); ok && !nextColdboot() {
+			r.Dispatch(
+				report.Degraded,
+				"rejecting coldboot loop",
+				err,
+			)
+			return false
+		}
+		r.Dispatch(
+			report.Inconsistent,
+			"consumed invalid message",
+			err,
+		)
+		return true
+	}, nil); dispatchErr != nil {
+		if _, ok := dispatchErr.(uevent.Recoverable); !ok {
+			r.Dispatch(
+				report.Fatal,
+				"discontinuing uevent processing due to nonrecoverable error",
+				dispatchErr,
+			)
+			return
+		}
+
+		if _, ok := dispatchErr.(uevent.NeedsColdboot); ok {
+			// coldboot loop rejected by handler
+			coldboot = false
+		}
+
+		goto retry
+	}
+}