Add collector for PCIe devices with link information

The link status of PCIe devices sometimes changes,
like link or speed downgrades, and devices disappear.
This patch collects PCIe devices' link infromation  to detect such failures.

As a first step, this collector exports PCIe devices'
- Device information (vendor_id, device_id, etc.)
- Parent PCIe device (e.g. PCIe bridge, PCIe switch)
- Link status (max_link_{speed|width}, current_link_{speed|width})

Signed-off-by: Naoki MATSUMOTO <m.naoki9911@gmail.com>

Author: naoki9911

collector/pci_device_linux.go

@@ -0,0 +1,135 @@
+// Copyright 2017-2019 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build !nopcidevice
+// +build !nopcidevice
+
+package collector
+
+import (
+	"errors"
+	"fmt"
+	"log/slog"
+	"os"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/procfs/sysfs"
+)
+
+type pciDeviceCollector struct {
+	fs          sysfs.FS
+	metricDescs map[string]*prometheus.Desc
+	logger      *slog.Logger
+	subsystem   string
+}
+
+func init() {
+	registerCollector("pcidevice", defaultEnabled, NewPciDeviceCollector)
+}
+
+// NewPciDeviceCollector returns a new Collector exposing PCI devices stats.
+func NewPciDeviceCollector(logger *slog.Logger) (Collector, error) {
+	var i pciDeviceCollector
+	var err error
+
+	i.fs, err = sysfs.NewFS(*sysPath)
+	if err != nil {
+		return nil, fmt.Errorf("failed to open sysfs: %w", err)
+	}
+	i.logger = logger
+
+	// Detailed description for all metrics.
+	descriptions := map[string]string{
+		"max_link_speed":     "Value of maximum link speed (GT/s)",
+		"max_link_width":     "Value of maximum link width (number of lanes)",
+		"current_link_speed": "Value of current link speed (GT/s)",
+		"current_link_width": "Value of current link width (number of lanes)",
+	}
+
+	i.metricDescs = make(map[string]*prometheus.Desc)
+	i.subsystem = "pcidevice"
+
+	for metricName, description := range descriptions {
+		i.metricDescs[metricName] = prometheus.NewDesc(
+			prometheus.BuildFQName(namespace, i.subsystem, metricName),
+			description,
+			[]string{"segment", "bus", "device", "function"},
+			nil,
+		)
+	}
+
+	return &i, nil
+}
+
+func (c *pciDeviceCollector) pushMetric(ch chan<- prometheus.Metric, name string, value *float64, location sysfs.PciDeviceLocation, valueType prometheus.ValueType) {
+	if value != nil {
+		ch <- prometheus.MustNewConstMetric(c.metricDescs[name], valueType, *value, location.Strings()...)
+	}
+}
+
+func (c *pciDeviceCollector) Update(ch chan<- prometheus.Metric) error {
+	devices, err := c.fs.PciDevices()
+	if err != nil {
+		if errors.Is(err, os.ErrNotExist) {
+			c.logger.Debug("infiniband statistics not found, skipping")
+			return ErrNoData
+		}
+		return fmt.Errorf("error obtaining InfiniBand class info: %w", err)
+	}
+
+	for _, device := range devices {
+
+		// The format follows the definition in drivers/pci/pci-sysfs.c
+		infos := [][]string{
+			[]string{"class_id", fmt.Sprintf("0x%06x", device.Class)},
+			[]string{"vendor_id", fmt.Sprintf("0x%04x", device.Device)},
+			[]string{"subsystem_vendor_id", fmt.Sprintf("0x%04x", device.SubsystemVendor)},
+			[]string{"subsystem_device_id", fmt.Sprintf("0x%04x", device.SubsystemDevice)},
+			[]string{"revision", fmt.Sprintf("0x%02x", device.Revision)},
+		}
+
+		labels := []string{}
+		values := []string{}
+		for i := range infos {
+			labels = append(labels, infos[i][0])
+			values = append(values, infos[i][1])
+		}
+
+		// The device location is represented in separated format.
+		labels = append(labels, []string{"segment", "bus", "device", "function"}...)
+		values = append(values, device.Location.Strings()...)
+
+		labels = append(labels, []string{"parent_segment", "parent_bus", "parent_device", "parent_function"}...)
+		if device.ParentLocation != nil {
+			values = append(values, device.ParentLocation.Strings()...)
+		} else {
+			// TODO: is this ok?
+			values = append(values, []string{"*", "*", "*", "*"}...)
+		}
+
+		infoDesc := prometheus.NewDesc(
+			prometheus.BuildFQName(namespace, c.subsystem, "info"),
+			"Non-numeric data from /sys/bus/pci/devices/<location>, value is always 1.",
+			labels,
+			nil,
+		)
+		ch <- prometheus.MustNewConstMetric(infoDesc, prometheus.GaugeValue, 1.0, values...)
+
+		c.pushMetric(ch, "max_link_speed", device.MaxLinkSpeed, device.Location, prometheus.GaugeValue)
+		c.pushMetric(ch, "max_link_width", device.MaxLinkWidth, device.Location, prometheus.GaugeValue)
+		c.pushMetric(ch, "current_link_speed", device.CurrentLinkSpeed, device.Location, prometheus.GaugeValue)
+		c.pushMetric(ch, "current_link_width", device.CurrentLinkWidth, device.Location, prometheus.GaugeValue)
+	}
+
+	return nil
+}