feat: support to get rotational of the disk.

[zhucan]

		content, err := os.ReadFile(fmt.Sprintf("/sys/block/%s/queue/rotational", dev))
		if err != nil {
			level.Debug(c.logger).Log("msg", "Failed to get sys block device queue stats", "err", err)
		}
		rotational := strings.Replace(string(content), "\n", "", -1)
		i, err := strconv.Atoi(rotational)

[tjhop]

For what it's worth, there is already code in place to get rotational info as reported by udev:

node_exporter/collector/diskstats_linux.go

Lines 252 to 258 in 94ef5cc

	udevIDATARotationRateRPM: {
	desc: prometheus.NewDesc(prometheus.BuildFQName(namespace, diskSubsystem, "ata_rotation_rate_rpm"),
	"ATA disk rotation rate in RPMs (0 for SSDs).",
	[]string{"device"},
	nil,
	), valueType: prometheus.GaugeValue,
	},

However, I don't have that metric available on any of the systems I personally own, and I do have rotational info in sysfs for my disks. I would also be in favor of a sysfs based method for collecting rotational info, but it might be better suited to live in github.com/prometheus/procfs, in my opinion

[tjhop]

Turns out it already does exist in procfs and I forgot about it!

https://pkg.go.dev/github.com/prometheus/procfs@v0.13.0/blockdevice#BlockQueueStats

Seems we would just need to utilize it

[SuperQ]

Yes, this seems like it would be easy to add to the diskstats collector.