zfs/cmd/zvol_wait/zvol_wait

#!/bin/sh

count_zvols() {
	if [ -z "$zvols" ]; then
		echo 0
	else
		echo "$zvols" | wc -l
	fi
}

filter_out_zvols_with_links() {
	while read -r zvol; do
		if [ ! -L "/dev/zvol/$zvol" ]; then
			echo "$zvol"
		fi
	done
}

filter_out_deleted_zvols() {
	while read -r zvol; do
		if zfs list "$zvol" >/dev/null 2>&1; then
			echo "$zvol"
		fi
	done
}

list_zvols() {
	zfs list -t volume -H -o \
		name,volmode,receive_resume_token,redact_snaps |
		while read -r zvol_line; do
		name=$(echo "$zvol_line" | awk '{print $1}')
		volmode=$(echo "$zvol_line" | awk '{print $2}')
		token=$(echo "$zvol_line" | awk '{print $3}')
		redacted=$(echo "$zvol_line" | awk '{print $4}')
		#
		# /dev links are not created for zvols with volmode = "none"
		# or for redacted zvols.
		#
		[ "$volmode" = "none" ] && continue
		[ "$redacted" = "-" ] || continue
		#
		# We also also ignore partially received zvols if it is
		# not an incremental receive, as those won't even have a block
		# device minor node created yet.
		#
		if [ "$token" != "-" ]; then
			#
			# Incremental receives create an invisible clone that
			# is not automatically displayed by zfs list.
			#
			if ! zfs list "$name/%recv" >/dev/null 2>&1; then
				continue
			fi
		fi
		echo "$name"
	done
}

zvols=$(list_zvols)
zvols_count=$(count_zvols)
if [ "$zvols_count" -eq 0 ]; then
	echo "No zvols found, nothing to do."
	exit 0
fi

echo "Testing $zvols_count zvol links"

outer_loop=0
while [ "$outer_loop" -lt 20 ]; do
	outer_loop=$((outer_loop + 1))

	old_zvols_count=$(count_zvols)

	inner_loop=0
	while [ "$inner_loop" -lt 30 ]; do
		inner_loop=$((inner_loop + 1))

		zvols="$(echo "$zvols" | filter_out_zvols_with_links)"

		zvols_count=$(count_zvols)
		if [ "$zvols_count" -eq 0 ]; then
			echo "All zvol links are now present."
			exit 0
		fi
		sleep 1
	done

	echo "Still waiting on $zvols_count zvol links ..."
	#
	# Although zvols should normally not be deleted at boot time,
	# if that is the case then their links will be missing and
	# we would stall.
	#
	if [ "$old_zvols_count" -eq "$zvols_count" ]; then
		echo "No progress since last loop."
		echo "Checking if any zvols were deleted."

		zvols=$(echo "$zvols" | filter_out_deleted_zvols)
		zvols_count=$(count_zvols)

		if [ "$old_zvols_count" -ne "$zvols_count" ]; then
			echo "$((old_zvols_count - zvols_count)) zvol(s) deleted."
		fi

		if [ "$zvols_count" -ne 0 ]; then
			echo "Remaining zvols:"
			echo "$zvols"
		else
			echo "All zvol links are now present."
			exit 0
		fi
	fi
done

echo "Timed out waiting on zvol links"
exit 1