Add btrfs device error stats (#2193)

* Improve metrics filesystem scanning logic
* Makes ioctl syscalls to load the device error stats.
* Adds filesystem mountpoint labels to existing metrics for ease of use.

Signed-off-by: Marcus Cobden <leth@users.noreply.github.com>

Author: leth

collector/btrfs_linux.go

@@ -18,8 +18,13 @@ package collector
 
 import (
 	"fmt"
+	"path"
+	"strings"
+	"syscall"
 
+	dennwc "github.com/dennwc/btrfs"
 	"github.com/go-kit/log"
+	"github.com/go-kit/log/level"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/procfs/btrfs"
 )
@@ -52,34 +57,178 @@ func NewBtrfsCollector(logger log.Logger) (Collector, error) {
 func (c *btrfsCollector) Update(ch chan<- prometheus.Metric) error {
 	stats, err := c.fs.Stats()
 	if err != nil {
-		return fmt.Errorf("failed to retrieve Btrfs stats: %w", err)
+		return fmt.Errorf("failed to retrieve Btrfs stats from procfs: %w", err)
+	}
+
+	ioctlStatsMap, err := c.getIoctlStats()
+	if err != nil {
+		level.Debug(c.logger).Log(
+			"msg", "Error querying btrfs device stats with ioctl",
+			"err", err)
+		ioctlStatsMap = make(map[string]*btrfsIoctlFsStats)
 	}
 
 	for _, s := range stats {
-		c.updateBtrfsStats(ch, s)
+		// match up procfs and ioctl info by filesystem UUID (without dashes)
+		var fsUUID = strings.Replace(s.UUID, "-", "", -1)
+		ioctlStats := ioctlStatsMap[fsUUID]
+		c.updateBtrfsStats(ch, s, ioctlStats)
 	}
 
 	return nil
 }
 
+type btrfsIoctlFsDevStats struct {
+	path string
+	uuid string
+
+	bytesUsed  uint64
+	totalBytes uint64
+
+	// The error stats below match the following upstream lists:
+	// https://github.com/dennwc/btrfs/blob/b3db0b2dedac3bf580f412034d77e0bf4b420167/btrfs.go#L132-L140
+	// https://github.com/torvalds/linux/blob/70d605cbeecb408dd884b1f0cd3963eeeaac144c/include/uapi/linux/btrfs.h#L680-L692
+	writeErrs      uint64
+	readErrs       uint64
+	flushErrs      uint64
+	corruptionErrs uint64
+	generationErrs uint64
+}
+
+type btrfsIoctlFsStats struct {
+	uuid    string
+	devices []btrfsIoctlFsDevStats
+}
+
+func (c *btrfsCollector) getIoctlStats() (map[string]*btrfsIoctlFsStats, error) {
+	// Instead of introducing more ioctl calls to scan for all btrfs
+	// filesytems re-use our mount point utils to find known mounts
+	mountsList, err := mountPointDetails(c.logger)
+	if err != nil {
+		return nil, err
+	}
+
+	// track devices we have successfully scanned, by device path
+	devicesDone := make(map[string]struct{})
+	// filesystems scann results by UUID
+	fsStats := make(map[string]*btrfsIoctlFsStats)
+
+	for _, mount := range mountsList {
+		if mount.fsType != "btrfs" {
+			continue
+		}
+
+		if _, found := devicesDone[mount.device]; found {
+			// We already found this filesystem by another mount point
+			continue
+		}
+
+		fs, err := dennwc.Open(mount.mountPoint, true)
+		if err != nil {
+			// failed to open this mount point, maybe we didn't have permission
+			// maybe we'll find another mount point for this FS later
+			level.Debug(c.logger).Log(
+				"msg", "Error inspecting btrfs mountpoint",
+				"mountPoint", mount.mountPoint,
+				"err", err)
+			continue
+		}
+
+		fsInfo, err := fs.Info()
+		if err != nil {
+			// Failed to get the FS info for some reason,
+			// perhaps it'll work with a different mount point
+			level.Debug(c.logger).Log(
+				"msg", "Error querying btrfs filesystem",
+				"mountPoint", mount.mountPoint,
+				"err", err)
+			continue
+		}
+
+		fsID := fsInfo.FSID.String()
+		if _, found := fsStats[fsID]; found {
+			// We already found this filesystem by another mount point
+			continue
+		}
+
+		deviceStats, err := c.getIoctlDeviceStats(fs, &fsInfo)
+		if err != nil {
+			level.Debug(c.logger).Log(
+				"msg", "Error querying btrfs device stats",
+				"mountPoint", mount.mountPoint,
+				"err", err)
+			continue
+		}
+
+		devicesDone[mount.device] = struct{}{}
+		fsStats[fsID] = &btrfsIoctlFsStats{
+			uuid:    fsID,
+			devices: deviceStats,
+		}
+	}
+
+	return fsStats, nil
+}
+
+func (c *btrfsCollector) getIoctlDeviceStats(fs *dennwc.FS, fsInfo *dennwc.Info) ([]btrfsIoctlFsDevStats, error) {
+	devices := make([]btrfsIoctlFsDevStats, 0, fsInfo.NumDevices)
+
+	for i := uint64(0); i <= fsInfo.MaxID; i++ {
+		deviceInfo, err := fs.GetDevInfo(i)
+
+		if err != nil {
+			if errno, ok := err.(syscall.Errno); ok && errno == syscall.ENODEV {
+				// device IDs do not consistently start at 0, nor are ranges contiguous, so we expect this
+				continue
+			}
+			return nil, err
+		}
+
+		deviceStats, err := fs.GetDevStats(i)
+		if err != nil {
+			return nil, err
+		}
+
+		devices = append(devices, btrfsIoctlFsDevStats{
+			path:       deviceInfo.Path,
+			uuid:       deviceInfo.UUID.String(),
+			bytesUsed:  deviceInfo.BytesUsed,
+			totalBytes: deviceInfo.TotalBytes,
+
+			writeErrs:      deviceStats.WriteErrs,
+			readErrs:       deviceStats.ReadErrs,
+			flushErrs:      deviceStats.FlushErrs,
+			corruptionErrs: deviceStats.CorruptionErrs,
+			generationErrs: deviceStats.GenerationErrs,
+		})
+
+		if uint64(len(devices)) == fsInfo.NumDevices {
+			break
+		}
+	}
+
+	return devices, nil
+}
+
 // btrfsMetric represents a single Btrfs metric that is converted into a Prometheus Metric.
 type btrfsMetric struct {
 	name            string
+	metricType      prometheus.ValueType
 	desc            string
 	value           float64
 	extraLabel      []string
 	extraLabelValue []string
 }
 
 // updateBtrfsStats collects statistics for one bcache ID.
-func (c *btrfsCollector) updateBtrfsStats(ch chan<- prometheus.Metric, s *btrfs.Stats) {
+func (c *btrfsCollector) updateBtrfsStats(ch chan<- prometheus.Metric, s *btrfs.Stats, ioctlStats *btrfsIoctlFsStats) {
 	const subsystem = "btrfs"
 
 	// Basic information about the filesystem.
 	devLabels := []string{"uuid"}
 
 	// Retrieve the metrics.
-	metrics := c.getMetrics(s)
+	metrics := c.getMetrics(s, ioctlStats)
 
 	// Convert all gathered metrics to Prometheus Metrics and add to channel.
 	for _, m := range metrics {
@@ -99,46 +248,112 @@ func (c *btrfsCollector) updateBtrfsStats(ch chan<- prometheus.Metric, s *btrfs.
 
 		ch <- prometheus.MustNewConstMetric(
 			desc,
-			prometheus.GaugeValue,
+			m.metricType,
 			m.value,
 			labelValues...,
 		)
 	}
 }
 
 // getMetrics returns metrics for the given Btrfs statistics.
-func (c *btrfsCollector) getMetrics(s *btrfs.Stats) []btrfsMetric {
+func (c *btrfsCollector) getMetrics(s *btrfs.Stats, ioctlStats *btrfsIoctlFsStats) []btrfsMetric {
 	metrics := []btrfsMetric{
 		{
 			name:            "info",
 			desc:            "Filesystem information",
 			value:           1,
+			metricType:      prometheus.GaugeValue,
 			extraLabel:      []string{"label"},
 			extraLabelValue: []string{s.Label},
 		},
 		{
-			name:  "global_rsv_size_bytes",
-			desc:  "Size of global reserve.",
-			value: float64(s.Allocation.GlobalRsvSize),
+			name:       "global_rsv_size_bytes",
+			desc:       "Size of global reserve.",
+			metricType: prometheus.GaugeValue,
+			value:      float64(s.Allocation.GlobalRsvSize),
 		},
 	}
 
-	// Information about devices.
-	for n, dev := range s.Devices {
-		metrics = append(metrics, btrfsMetric{
-			name:            "device_size_bytes",
-			desc:            "Size of a device that is part of the filesystem.",
-			value:           float64(dev.Size),
-			extraLabel:      []string{"device"},
-			extraLabelValue: []string{n},
-		})
-	}
-
 	// Information about data, metadata and system data.
 	metrics = append(metrics, c.getAllocationStats("data", s.Allocation.Data)...)
 	metrics = append(metrics, c.getAllocationStats("metadata", s.Allocation.Metadata)...)
 	metrics = append(metrics, c.getAllocationStats("system", s.Allocation.System)...)
 
+	// Information about devices.
+	if ioctlStats == nil {
+		for n, dev := range s.Devices {
+			metrics = append(metrics, btrfsMetric{
+				name:            "device_size_bytes",
+				desc:            "Size of a device that is part of the filesystem.",
+				metricType:      prometheus.GaugeValue,
+				value:           float64(dev.Size),
+				extraLabel:      []string{"device"},
+				extraLabelValue: []string{n},
+			})
+		}
+		return metrics
+	}
+
+	for _, dev := range ioctlStats.devices {
+		// trim the path prefix from the device name so the value should match
+		// the value used in the fallback branch above.
+		// e.g. /dev/sda -> sda, /rootfs/dev/md1 -> md1
+		_, device := path.Split(dev.path)
+
+		extraLabels := []string{"device", "btrfs_dev_uuid"}
+		extraLabelValues := []string{device, dev.uuid}
+
+		metrics = append(metrics,
+			btrfsMetric{
+				name:            "device_size_bytes",
+				desc:            "Size of a device that is part of the filesystem.",
+				metricType:      prometheus.GaugeValue,
+				value:           float64(dev.totalBytes),
+				extraLabel:      extraLabels,
+				extraLabelValue: extraLabelValues,
+			},
+			// A bytes available metric is probably more useful than a
+			// bytes used metric, because large numbers of bytes will
+			// suffer from floating point representation issues
+			// and we probably care more about the number when it's low anyway
+			btrfsMetric{
+				name:            "device_unused_bytes",
+				desc:            "Unused bytes unused on a device that is part of the filesystem.",
+				metricType:      prometheus.GaugeValue,
+				value:           float64(dev.totalBytes - dev.bytesUsed),
+				extraLabel:      extraLabels,
+				extraLabelValue: extraLabelValues,
+			})
+
+		errorLabels := append([]string{"type"}, extraLabels...)
+		values := []uint64{
+			dev.writeErrs,
+			dev.readErrs,
+			dev.flushErrs,
+			dev.corruptionErrs,
+			dev.generationErrs,
+		}
+		btrfsErrorTypeNames := []string{
+			"write",
+			"read",
+			"flush",
+			"corruption",
+			"generation",
+		}
+
+		for i, errorType := range btrfsErrorTypeNames {
+			metrics = append(metrics,
+				btrfsMetric{
+					name:            "device_errors_total",
+					desc:            "Errors reported for the device",
+					metricType:      prometheus.CounterValue,
+					value:           float64(values[i]),
+					extraLabel:      errorLabels,
+					extraLabelValue: append([]string{errorType}, extraLabelValues...),
+				})
+		}
+	}
+
 	return metrics
 }
 
@@ -148,6 +363,7 @@ func (c *btrfsCollector) getAllocationStats(a string, s *btrfs.AllocationStats)
 		{
 			name:            "reserved_bytes",
 			desc:            "Amount of space reserved for a data type",
+			metricType:      prometheus.GaugeValue,
 			value:           float64(s.ReservedBytes),
 			extraLabel:      []string{"block_group_type"},
 			extraLabelValue: []string{a},
@@ -168,20 +384,23 @@ func (c *btrfsCollector) getLayoutStats(a, l string, s *btrfs.LayoutUsage) []btr
 		{
 			name:            "used_bytes",
 			desc:            "Amount of used space by a layout/data type",
+			metricType:      prometheus.GaugeValue,
 			value:           float64(s.UsedBytes),
 			extraLabel:      []string{"block_group_type", "mode"},
 			extraLabelValue: []string{a, l},
 		},
 		{
 			name:            "size_bytes",
 			desc:            "Amount of space allocated for a layout/data type",
+			metricType:      prometheus.GaugeValue,
 			value:           float64(s.TotalBytes),
 			extraLabel:      []string{"block_group_type", "mode"},
 			extraLabelValue: []string{a, l},
 		},
 		{
 			name:            "allocation_ratio",
 			desc:            "Data allocation ratio for a layout/data type",
+			metricType:      prometheus.GaugeValue,
 			value:           s.Ratio,
 			extraLabel:      []string{"block_group_type", "mode"},
 			extraLabelValue: []string{a, l},