Add Btrfs collector (#1512)

* Add procfs/btrfs to vendor folder
* Add Btrfs collector

Resolves #1100

Signed-off-by: Silke Hofstra <silke@slxh.eu>

9 files changed, 1272 insertions, 0 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 19d3cff..e04c9ad 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -23,6 +23,7 @@
 * [FEATURE] Add new cooling_device metrics to thermal zone collector #1445
 * [FEATURE] Add new softnet collector #1576
 * [FEATURE] Add RAPL collector #1523
+* [FEATURE] Add Btrfs collector #1512
 * [ENHANCEMENT] Collect InfiniBand port state and physical state #1357
 * [ENHANCEMENT] Include additional XFS runtime statistics. #1423
 * [ENHANCEMENT] Report non-fatal collection errors in the exporter metric. #1439
diff --git a/collector/btrfs_linux.go b/collector/btrfs_linux.go
new file mode 100644
index 0000000..2336e65
--- /dev/null
+++ b/collector/btrfs_linux.go
@@ -0,0 +1,189 @@
+// Copyright 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.
+
+// +build !nobtrfs
+
+package collector
+
+import (
+        "fmt"
+
+        "github.com/go-kit/kit/log"
+        "github.com/prometheus/client_golang/prometheus"
+        "github.com/prometheus/procfs/btrfs"
+)
+
+// A btrfsCollector is a Collector which gathers metrics from Btrfs filesystems.
+type btrfsCollector struct {
+        fs     btrfs.FS
+        logger log.Logger
+}
+
+func init() {
+        registerCollector("btrfs", defaultEnabled, NewBtrfsCollector)
+}
+
+// NewBtrfsCollector returns a new Collector exposing Btrfs statistics.
+func NewBtrfsCollector(logger log.Logger) (Collector, error) {
+        fs, err := btrfs.NewFS(*sysPath)
+        if err != nil {
+                return nil, fmt.Errorf("failed to open sysfs: %v", err)
+        }
+
+        return &btrfsCollector{
+                fs:     fs,
+                logger: logger,
+        }, nil
+}
+
+// Update retrieves and exports Btrfs statistics.
+// It implements Collector.
+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: %v", err)
+        }
+
+        for _, s := range stats {
+                c.updateBtrfsStats(ch, s)
+        }
+
+        return nil
+}
+
+// btrfsMetric represents a single Btrfs metric that is converted into a Prometheus Metric.
+type btrfsMetric struct {
+        name            string
+        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) {
+        const subsystem = "btrfs"
+
+        // Basic information about the filesystem.
+        devLabels := []string{"uuid"}
+
+        // Retrieve the metrics.
+        metrics := c.getMetrics(s)
+
+        // Convert all gathered metrics to Prometheus Metrics and add to channel.
+        for _, m := range metrics {
+                labels := append(devLabels, m.extraLabel...)
+
+                desc := prometheus.NewDesc(
+                        prometheus.BuildFQName(namespace, subsystem, m.name),
+                        m.desc,
+                        labels,
+                        nil,
+                )
+
+                labelValues := []string{s.UUID}
+                if len(m.extraLabelValue) > 0 {
+                        labelValues = append(labelValues, m.extraLabelValue...)
+                }
+
+                ch <- prometheus.MustNewConstMetric(
+                        desc,
+                        prometheus.GaugeValue,
+                        m.value,
+                        labelValues...,
+                )
+        }
+}
+
+// getMetrics returns metrics for the given Btrfs statistics.
+func (c *btrfsCollector) getMetrics(s *btrfs.Stats) []btrfsMetric {
+        metrics := []btrfsMetric{
+                {
+                        name:            "info",
+                        desc:            "Filesystem information",
+                        value:           1,
+                        extraLabel:      []string{"label"},
+                        extraLabelValue: []string{s.Label},
+                },
+                {
+                        name:  "global_rsv_size_bytes",
+                        desc:  "Size of global reserve.",
+                        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)...)
+
+        return metrics
+}
+
+// getAllocationStats returns allocation metrics for the given Btrfs Allocation statistics.
+func (c *btrfsCollector) getAllocationStats(a string, s *btrfs.AllocationStats) []btrfsMetric {
+        metrics := []btrfsMetric{
+                {
+                        name:            "reserved_bytes",
+                        desc:            "Amount of space reserved for a data type",
+                        value:           float64(s.ReservedBytes),
+                        extraLabel:      []string{"block_group_type"},
+                        extraLabelValue: []string{a},
+                },
+        }
+
+        // Add all layout statistics.
+        for layout, stats := range s.Layouts {
+                metrics = append(metrics, c.getLayoutStats(a, layout, stats)...)
+        }
+
+        return metrics
+}
+
+// getLayoutStats returns metrics for a data layout.
+func (c *btrfsCollector) getLayoutStats(a, l string, s *btrfs.LayoutUsage) []btrfsMetric {
+        return []btrfsMetric{
+                {
+                        name:            "used_bytes",
+                        desc:            "Amount of used space by a layout/data type",
+                        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",
+                        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",
+                        value:           s.Ratio,
+                        extraLabel:      []string{"block_group_type", "mode"},
+                        extraLabelValue: []string{a, l},
+                },
+        }
+}
diff --git a/collector/btrfs_linux_test.go b/collector/btrfs_linux_test.go
new file mode 100644
index 0000000..9db7419
--- /dev/null
+++ b/collector/btrfs_linux_test.go
@@ -0,0 +1,118 @@
+// Copyright 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.
+
+// +build !nobtrfs
+
+package collector
+
+import (
+        "strings"
+        "testing"
+
+        "github.com/prometheus/procfs/btrfs"
+)
+
+var expectedBtrfsMetrics = [][]btrfsMetric{
+        {
+                {name: "info", value: 1, extraLabel: []string{"label"}, extraLabelValue: []string{"fixture"}},
+                {name: "global_rsv_size_bytes", value: 1.6777216e+07},
+                {name: "device_size_bytes", value: 1.073741824e+10, extraLabel: []string{"device"}, extraLabelValue: []string{"loop25"}},
+                {name: "device_size_bytes", value: 1.073741824e+10, extraLabel: []string{"device"}, extraLabelValue: []string{"loop26"}},
+                {name: "reserved_bytes", value: 0, extraLabel: []string{"block_group_type"}, extraLabelValue: []string{"data"}},
+                {name: "used_bytes", value: 8.08189952e+08, extraLabel: []string{"block_group_type", "mode"}, extraLabelValue: []string{"data", "raid0"}},
+                {name: "size_bytes", value: 2.147483648e+09, extraLabel: []string{"block_group_type", "mode"}, extraLabelValue: []string{"data", "raid0"}},
+                {name: "allocation_ratio", value: 1, extraLabel: []string{"block_group_type", "mode"}, extraLabelValue: []string{"data", "raid0"}},
+                {name: "reserved_bytes", value: 0, extraLabel: []string{"block_group_type"}, extraLabelValue: []string{"metadata"}},
+                {name: "used_bytes", value: 933888, extraLabel: []string{"block_group_type", "mode"}, extraLabelValue: []string{"metadata", "raid1"}},
+                {name: "size_bytes", value: 1.073741824e+09, extraLabel: []string{"block_group_type", "mode"}, extraLabelValue: []string{"metadata", "raid1"}},
+                {name: "allocation_ratio", value: 2, extraLabel: []string{"block_group_type", "mode"}, extraLabelValue: []string{"metadata", "raid1"}},
+                {name: "reserved_bytes", value: 0, extraLabel: []string{"block_group_type"}, extraLabelValue: []string{"system"}},
+                {name: "used_bytes", value: 16384, extraLabel: []string{"block_group_type", "mode"}, extraLabelValue: []string{"system", "raid1"}},
+                {name: "size_bytes", value: 8.388608e+06, extraLabel: []string{"block_group_type", "mode"}, extraLabelValue: []string{"system", "raid1"}},
+                {name: "allocation_ratio", value: 2, extraLabel: []string{"block_group_type", "mode"}, extraLabelValue: []string{"system", "raid1"}},
+        },
+        {
+                {name: "info", value: 1, extraLabel: []string{"label"}, extraLabelValue: []string{""}},
+                {name: "global_rsv_size_bytes", value: 1.6777216e+07},
+                {name: "device_size_bytes", value: 1.073741824e+10, extraLabel: []string{"device"}, extraLabelValue: []string{"loop22"}},
+                {name: "device_size_bytes", value: 1.073741824e+10, extraLabel: []string{"device"}, extraLabelValue: []string{"loop23"}},
+                {name: "device_size_bytes", value: 1.073741824e+10, extraLabel: []string{"device"}, extraLabelValue: []string{"loop24"}},
+                {name: "device_size_bytes", value: 1.073741824e+10, extraLabel: []string{"device"}, extraLabelValue: []string{"loop25"}},
+                {name: "reserved_bytes", value: 0, extraLabel: []string{"block_group_type"}, extraLabelValue: []string{"data"}},
+                {name: "used_bytes", value: 0, extraLabel: []string{"block_group_type", "mode"}, extraLabelValue: []string{"data", "raid5"}},
+                {name: "size_bytes", value: 6.44087808e+08, extraLabel: []string{"block_group_type", "mode"}, extraLabelValue: []string{"data", "raid5"}},
+                {name: "allocation_ratio", value: 1.3333333333333333, extraLabel: []string{"block_group_type", "mode"}, extraLabelValue: []string{"data", "raid5"}},
+                {name: "reserved_bytes", value: 0, extraLabel: []string{"block_group_type"}, extraLabelValue: []string{"metadata"}},
+                {name: "used_bytes", value: 114688, extraLabel: []string{"block_group_type", "mode"}, extraLabelValue: []string{"metadata", "raid6"}},
+                {name: "size_bytes", value: 4.29391872e+08, extraLabel: []string{"block_group_type", "mode"}, extraLabelValue: []string{"metadata", "raid6"}},
+                {name: "allocation_ratio", value: 2, extraLabel: []string{"block_group_type", "mode"}, extraLabelValue: []string{"metadata", "raid6"}},
+                {name: "reserved_bytes", value: 0, extraLabel: []string{"block_group_type"}, extraLabelValue: []string{"system"}},
+                {name: "used_bytes", value: 16384, extraLabel: []string{"block_group_type", "mode"}, extraLabelValue: []string{"system", "raid6"}},
+                {name: "size_bytes", value: 1.6777216e+07, extraLabel: []string{"block_group_type", "mode"}, extraLabelValue: []string{"system", "raid6"}},
+                {name: "allocation_ratio", value: 2, extraLabel: []string{"block_group_type", "mode"}, extraLabelValue: []string{"system", "raid6"}},
+        },
+}
+
+func checkMetric(exp, got *btrfsMetric) bool {
+        if exp.name != got.name ||
+                exp.value != got.value ||
+                len(exp.extraLabel) != len(got.extraLabel) ||
+                len(exp.extraLabelValue) != len(got.extraLabelValue) {
+                return false
+        }
+
+        for i := range exp.extraLabel {
+                if exp.extraLabel[i] != got.extraLabel[i] {
+                        return false
+                }
+
+                // Devices (loopXX) can appear in random order, so just check the first 4 characters.
+                if strings.HasPrefix(got.extraLabelValue[i], "loop") &&
+                        exp.extraLabelValue[i][:4] == got.extraLabelValue[i][:4] {
+                        continue
+                }
+
+                if exp.extraLabelValue[i] != got.extraLabelValue[i] {
+                        return false
+                }
+        }
+
+        return true
+}
+
+func TestBtrfs(t *testing.T) {
+        fs, _ := btrfs.NewFS("fixtures/sys")
+        collector := &btrfsCollector{fs: fs}
+
+        stats, err := collector.fs.Stats()
+        if err != nil {
+                t.Fatalf("Failed to retrieve Btrfs stats: %v", err)
+        }
+        if len(stats) != len(expectedBtrfsMetrics) {
+                t.Fatalf("Unexpected number of Btrfs stats: expected %v, got %v", len(expectedBtrfsMetrics), len(stats))
+        }
+
+        for i, s := range stats {
+                metrics := collector.getMetrics(s)
+                if len(metrics) != len(expectedBtrfsMetrics[i]) {
+                        t.Fatalf("Unexpected number of Btrfs metrics: expected %v, got %v", len(expectedBtrfsMetrics[i]), len(metrics))
+                }
+
+                for j, m := range metrics {
+                        exp := expectedBtrfsMetrics[i][j]
+                        if !checkMetric(&exp, &m) {
+                                t.Errorf("Incorrect btrfs metric: expected %#v, got: %#v", exp, m)
+                        }
+                }
+        }
+}
diff --git a/collector/fixtures/e2e-output.txt b/collector/fixtures/e2e-output.txt
index e34bf56..ddc048f 100644
--- a/collector/fixtures/e2e-output.txt
+++ b/collector/fixtures/e2e-output.txt
@@ -140,6 +140,54 @@ node_bonding_slaves{master="int"} 2
 # HELP node_boot_time_seconds Node boot time, in unixtime.
 # TYPE node_boot_time_seconds gauge
 node_boot_time_seconds 1.418183276e+09
+# HELP node_btrfs_allocation_ratio Data allocation ratio for a layout/data type
+# TYPE node_btrfs_allocation_ratio gauge
+node_btrfs_allocation_ratio{block_group_type="data",mode="raid0",uuid="0abb23a9-579b-43e6-ad30-227ef47fcb9d"} 1
+node_btrfs_allocation_ratio{block_group_type="data",mode="raid5",uuid="7f07c59f-6136-449c-ab87-e1cf2328731b"} 1.3333333333333333
+node_btrfs_allocation_ratio{block_group_type="metadata",mode="raid1",uuid="0abb23a9-579b-43e6-ad30-227ef47fcb9d"} 2
+node_btrfs_allocation_ratio{block_group_type="metadata",mode="raid6",uuid="7f07c59f-6136-449c-ab87-e1cf2328731b"} 2
+node_btrfs_allocation_ratio{block_group_type="system",mode="raid1",uuid="0abb23a9-579b-43e6-ad30-227ef47fcb9d"} 2
+node_btrfs_allocation_ratio{block_group_type="system",mode="raid6",uuid="7f07c59f-6136-449c-ab87-e1cf2328731b"} 2
+# HELP node_btrfs_device_size_bytes Size of a device that is part of the filesystem.
+# TYPE node_btrfs_device_size_bytes gauge
+node_btrfs_device_size_bytes{device="loop22",uuid="7f07c59f-6136-449c-ab87-e1cf2328731b"} 1.073741824e+10
+node_btrfs_device_size_bytes{device="loop23",uuid="7f07c59f-6136-449c-ab87-e1cf2328731b"} 1.073741824e+10
+node_btrfs_device_size_bytes{device="loop24",uuid="7f07c59f-6136-449c-ab87-e1cf2328731b"} 1.073741824e+10
+node_btrfs_device_size_bytes{device="loop25",uuid="0abb23a9-579b-43e6-ad30-227ef47fcb9d"} 1.073741824e+10
+node_btrfs_device_size_bytes{device="loop25",uuid="7f07c59f-6136-449c-ab87-e1cf2328731b"} 1.073741824e+10
+node_btrfs_device_size_bytes{device="loop26",uuid="0abb23a9-579b-43e6-ad30-227ef47fcb9d"} 1.073741824e+10
+# HELP node_btrfs_global_rsv_size_bytes Size of global reserve.
+# TYPE node_btrfs_global_rsv_size_bytes gauge
+node_btrfs_global_rsv_size_bytes{uuid="0abb23a9-579b-43e6-ad30-227ef47fcb9d"} 1.6777216e+07
+node_btrfs_global_rsv_size_bytes{uuid="7f07c59f-6136-449c-ab87-e1cf2328731b"} 1.6777216e+07
+# HELP node_btrfs_info Filesystem information
+# TYPE node_btrfs_info gauge
+node_btrfs_info{label="",uuid="7f07c59f-6136-449c-ab87-e1cf2328731b"} 1
+node_btrfs_info{label="fixture",uuid="0abb23a9-579b-43e6-ad30-227ef47fcb9d"} 1
+# HELP node_btrfs_reserved_bytes Amount of space reserved for a data type
+# TYPE node_btrfs_reserved_bytes gauge
+node_btrfs_reserved_bytes{block_group_type="data",uuid="0abb23a9-579b-43e6-ad30-227ef47fcb9d"} 0
+node_btrfs_reserved_bytes{block_group_type="data",uuid="7f07c59f-6136-449c-ab87-e1cf2328731b"} 0
+node_btrfs_reserved_bytes{block_group_type="metadata",uuid="0abb23a9-579b-43e6-ad30-227ef47fcb9d"} 0
+node_btrfs_reserved_bytes{block_group_type="metadata",uuid="7f07c59f-6136-449c-ab87-e1cf2328731b"} 0
+node_btrfs_reserved_bytes{block_group_type="system",uuid="0abb23a9-579b-43e6-ad30-227ef47fcb9d"} 0
+node_btrfs_reserved_bytes{block_group_type="system",uuid="7f07c59f-6136-449c-ab87-e1cf2328731b"} 0
+# HELP node_btrfs_size_bytes Amount of space allocated for a layout/data type
+# TYPE node_btrfs_size_bytes gauge
+node_btrfs_size_bytes{block_group_type="data",mode="raid0",uuid="0abb23a9-579b-43e6-ad30-227ef47fcb9d"} 2.147483648e+09
+node_btrfs_size_bytes{block_group_type="data",mode="raid5",uuid="7f07c59f-6136-449c-ab87-e1cf2328731b"} 6.44087808e+08
+node_btrfs_size_bytes{block_group_type="metadata",mode="raid1",uuid="0abb23a9-579b-43e6-ad30-227ef47fcb9d"} 1.073741824e+09
+node_btrfs_size_bytes{block_group_type="metadata",mode="raid6",uuid="7f07c59f-6136-449c-ab87-e1cf2328731b"} 4.29391872e+08
+node_btrfs_size_bytes{block_group_type="system",mode="raid1",uuid="0abb23a9-579b-43e6-ad30-227ef47fcb9d"} 8.388608e+06
+node_btrfs_size_bytes{block_group_type="system",mode="raid6",uuid="7f07c59f-6136-449c-ab87-e1cf2328731b"} 1.6777216e+07
+# HELP node_btrfs_used_bytes Amount of used space by a layout/data type
+# TYPE node_btrfs_used_bytes gauge
+node_btrfs_used_bytes{block_group_type="data",mode="raid0",uuid="0abb23a9-579b-43e6-ad30-227ef47fcb9d"} 8.08189952e+08
+node_btrfs_used_bytes{block_group_type="data",mode="raid5",uuid="7f07c59f-6136-449c-ab87-e1cf2328731b"} 0
+node_btrfs_used_bytes{block_group_type="metadata",mode="raid1",uuid="0abb23a9-579b-43e6-ad30-227ef47fcb9d"} 933888
+node_btrfs_used_bytes{block_group_type="metadata",mode="raid6",uuid="7f07c59f-6136-449c-ab87-e1cf2328731b"} 114688
+node_btrfs_used_bytes{block_group_type="system",mode="raid1",uuid="0abb23a9-579b-43e6-ad30-227ef47fcb9d"} 16384
+node_btrfs_used_bytes{block_group_type="system",mode="raid6",uuid="7f07c59f-6136-449c-ab87-e1cf2328731b"} 16384
 # HELP node_buddyinfo_blocks Count of free blocks according to size.
 # TYPE node_buddyinfo_blocks gauge
 node_buddyinfo_blocks{node="0",size="0",zone="DMA"} 1
@@ -2560,6 +2608,7 @@ node_schedstat_waiting_seconds_total{cpu="1"} 364107.263788241
 node_scrape_collector_success{collector="arp"} 1
 node_scrape_collector_success{collector="bcache"} 1
 node_scrape_collector_success{collector="bonding"} 1
+node_scrape_collector_success{collector="btrfs"} 1
 node_scrape_collector_success{collector="buddyinfo"} 1
 node_scrape_collector_success{collector="conntrack"} 1
 node_scrape_collector_success{collector="cpu"} 1
diff --git a/collector/fixtures/sys.ttar b/collector/fixtures/sys.ttar
index 47610fe..a4550a5 100644
--- a/collector/fixtures/sys.ttar
+++ b/collector/fixtures/sys.ttar
@@ -3233,6 +3233,601 @@ Lines: 1
 0
 Mode: 644
 # ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+Directory: sys/fs/btrfs
+Mode: 755
+# ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+Directory: sys/fs/btrfs/0abb23a9-579b-43e6-ad30-227ef47fcb9d
+Mode: 755
+# ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+Directory: sys/fs/btrfs/0abb23a9-579b-43e6-ad30-227ef47fcb9d/allocation
+Mode: 755
+# ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+Directory: sys/fs/btrfs/0abb23a9-579b-43e6-ad30-227ef47fcb9d/allocation/data
+Mode: 755
+# ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+Path: sys/fs/btrfs/0abb23a9-579b-43e6-ad30-227ef47fcb9d/allocation/data/bytes_may_use
+Lines: 1
+0
+Mode: 444
+# ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+Path: sys/fs/btrfs/0abb23a9-579b-43e6-ad30-227ef47fcb9d/allocation/data/bytes_pinned
+Lines: 1
+0
+Mode: 444
+# ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+Path: sys/fs/btrfs/0abb23a9-579b-43e6-ad30-227ef47fcb9d/allocation/data/bytes_readonly
+Lines: 1
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diff --git a/end-to-end-test.sh b/end-to-end-test.sh
index 6d0bce3..fb1520d 100755
--- a/end-to-end-test.sh
+++ b/end-to-end-test.sh
@@ -5,6 +5,7 @@ set -euf -o pipefail
 enabled_collectors=$(cat << COLLECTORS
   arp
   bcache
+  btrfs
   buddyinfo
   conntrack
   cpu
diff --git a/vendor/github.com/prometheus/procfs/btrfs/btrfs.go b/vendor/github.com/prometheus/procfs/btrfs/btrfs.go
new file mode 100644
index 0000000..094c898
--- /dev/null
+++ b/vendor/github.com/prometheus/procfs/btrfs/btrfs.go
@@ -0,0 +1,67 @@
+// Copyright 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.
+
+// Package btrfs provides access to statistics exposed by Btrfs filesystems.
+package btrfs
+
+// Stats contains statistics for a single Btrfs filesystem.
+// See Linux fs/btrfs/sysfs.c for more information.
+type Stats struct {
+        UUID, Label    string
+        Allocation     Allocation
+        Devices        map[string]*Device
+        Features       []string
+        CloneAlignment uint64
+        NodeSize       uint64
+        QuotaOverride  uint64
+        SectorSize     uint64
+}
+
+// Allocation contains allocation statistics for data, metadata and system data.
+type Allocation struct {
+        GlobalRsvReserved, GlobalRsvSize uint64
+        Data, Metadata, System           *AllocationStats
+}
+
+// AllocationStats contains allocation statistics for a data type.
+type AllocationStats struct {
+        // Usage statistics
+        DiskUsedBytes    uint64
+        DiskTotalBytes   uint64
+        MayUseBytes      uint64
+        PinnedBytes      uint64
+        TotalPinnedBytes uint64
+        ReadOnlyBytes    uint64
+        ReservedBytes    uint64
+        UsedBytes        uint64
+        TotalBytes       uint64
+
+        // Flags marking filesystem state
+        // See Linux fs/btrfs/ctree.h for more information.
+        Flags uint64
+
+        // Additional disk usage statistics depending on the disk layout.
+        // At least one of these will exist and not be nil.
+        Layouts map[string]*LayoutUsage
+}
+
+// LayoutUsage contains additional usage statistics for a disk layout.
+type LayoutUsage struct {
+        UsedBytes, TotalBytes uint64
+        Ratio                 float64
+}
+
+// Device contains information about a device that is part of a Btrfs filesystem.
+type Device struct {
+        Size uint64
+}
diff --git a/vendor/github.com/prometheus/procfs/btrfs/get.go b/vendor/github.com/prometheus/procfs/btrfs/get.go
new file mode 100644
index 0000000..fa70daa
--- /dev/null
+++ b/vendor/github.com/prometheus/procfs/btrfs/get.go
@@ -0,0 +1,251 @@
+// Copyright 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.
+
+package btrfs
+
+import (
+        "io/ioutil"
+        "os"
+        "path"
+        "path/filepath"
+        "strconv"
+        "strings"
+
+        "github.com/prometheus/procfs/internal/fs"
+        "github.com/prometheus/procfs/internal/util"
+)
+
+// SectorSize contains the Linux sector size.
+// > Linux always considers sectors to be 512 bytes long independently
+// > of the devices real block size.
+const SectorSize = 512
+
+// FS represents the pseudo-filesystem sys, which provides an interface to
+// kernel data structures.
+type FS struct {
+        sys *fs.FS
+}
+
+// NewDefaultFS returns a new Bcache using the default sys fs mount point. It will error
+// if the mount point can't be read.
+func NewDefaultFS() (FS, error) {
+        return NewFS(fs.DefaultSysMountPoint)
+}
+
+// NewFS returns a new Btrfs filesystem using the given sys fs mount point. It will error
+// if the mount point can't be read.
+func NewFS(mountPoint string) (FS, error) {
+        if strings.TrimSpace(mountPoint) == "" {
+                mountPoint = fs.DefaultSysMountPoint
+        }
+        sys, err := fs.NewFS(mountPoint)
+        if err != nil {
+                return FS{}, err
+        }
+        return FS{&sys}, nil
+}
+
+// Stats retrieves Btrfs filesystem runtime statistics for each mounted Btrfs filesystem.
+func (fs FS) Stats() ([]*Stats, error) {
+        matches, err := filepath.Glob(fs.sys.Path("fs/btrfs/*-*"))
+        if err != nil {
+                return nil, err
+        }
+
+        stats := make([]*Stats, 0, len(matches))
+        for _, uuidPath := range matches {
+                s, err := GetStats(uuidPath)
+                if err != nil {
+                        return nil, err
+                }
+
+                // Set the UUID from the path when it could not be retrieved from the filesystem.
+                if s.UUID == "" {
+                        s.UUID = filepath.Base(uuidPath)
+                }
+
+                stats = append(stats, s)
+        }
+
+        return stats, nil
+}
+
+// GetStats collects all Btrfs statistics from sysfs
+func GetStats(uuidPath string) (*Stats, error) {
+        r := &reader{path: uuidPath}
+        s := r.readFilesystemStats()
+        if r.err != nil {
+                return nil, r.err
+        }
+
+        return s, nil
+}
+
+type reader struct {
+        path     string
+        err      error
+        devCount int
+}
+
+// readFile reads a file relative to the path of the reader.
+// Non-existing files are ignored.
+func (r *reader) readFile(n string) string {
+        b, err := util.SysReadFile(path.Join(r.path, n))
+        if err != nil && !os.IsNotExist(err) {
+                r.err = err
+        }
+        return strings.TrimSpace(string(b))
+}
+
+// readValues reads a number of numerical values into an uint64 slice.
+func (r *reader) readValue(n string) (v uint64) {
+        // Read value from file
+        s := r.readFile(n)
+        if r.err != nil {
+                return
+        }
+
+        // Convert number
+        v, _ = strconv.ParseUint(s, 10, 64)
+        return
+}
+
+// listFiles returns a list of files for a directory of the reader.
+func (r *reader) listFiles(p string) []string {
+        files, err := ioutil.ReadDir(path.Join(r.path, p))
+        if err != nil {
+                r.err = err
+                return nil
+        }
+
+        names := make([]string, len(files))
+        for i, f := range files {
+                names[i] = f.Name()
+        }
+        return names
+}
+
+// readAllocationStats reads Btrfs allocation data for the current path.
+func (r *reader) readAllocationStats(d string) (a *AllocationStats) {
+        // Create a reader for this subdirectory
+        sr := &reader{path: path.Join(r.path, d), devCount: r.devCount}
+
+        // Get the stats
+        a = &AllocationStats{
+                // Read basic allocation stats
+                MayUseBytes:      sr.readValue("bytes_may_use"),
+                PinnedBytes:      sr.readValue("bytes_pinned"),
+                ReadOnlyBytes:    sr.readValue("bytes_readonly"),
+                ReservedBytes:    sr.readValue("bytes_reserved"),
+                UsedBytes:        sr.readValue("bytes_used"),
+                DiskUsedBytes:    sr.readValue("disk_used"),
+                DiskTotalBytes:   sr.readValue("disk_total"),
+                Flags:            sr.readValue("flags"),
+                TotalBytes:       sr.readValue("total_bytes"),
+                TotalPinnedBytes: sr.readValue("total_bytes_pinned"),
+                Layouts:          sr.readLayouts(),
+        }
+
+        // Pass any error back
+        r.err = sr.err
+
+        return
+}
+
+// readLayouts reads all Btrfs layout statistics for the current path
+func (r *reader) readLayouts() map[string]*LayoutUsage {
+        files, err := ioutil.ReadDir(r.path)
+        if err != nil {
+                r.err = err
+                return nil
+        }
+
+        m := make(map[string]*LayoutUsage)
+        for _, f := range files {
+                if f.IsDir() {
+                        m[f.Name()] = r.readLayout(f.Name())
+                }
+        }
+
+        return m
+}
+
+// readLayout reads the Btrfs layout statistics for an allocation layout.
+func (r *reader) readLayout(p string) (l *LayoutUsage) {
+        l = new(LayoutUsage)
+        l.TotalBytes = r.readValue(path.Join(p, "total_bytes"))
+        l.UsedBytes = r.readValue(path.Join(p, "used_bytes"))
+        l.Ratio = r.calcRatio(p)
+
+        return
+}
+
+// calcRatio returns the calculated ratio for a layout mode.
+func (r *reader) calcRatio(p string) float64 {
+        switch p {
+        case "single", "raid0":
+                return 1
+        case "dup", "raid1", "raid10":
+                return 2
+        case "raid5":
+                return float64(r.devCount) / (float64(r.devCount) - 1)
+        case "raid6":
+                return float64(r.devCount) / (float64(r.devCount) - 2)
+        default:
+                return 0
+        }
+}
+
+// readDeviceInfo returns the information for all devices associated with this filesystem.
+func (r *reader) readDeviceInfo(d string) map[string]*Device {
+        devs := r.listFiles("devices")
+        info := make(map[string]*Device, len(devs))
+        for _, n := range devs {
+                info[n] = &Device{
+                        Size: SectorSize * r.readValue("devices/"+n+"/size"),
+                }
+        }
+
+        return info
+}
+
+// readFilesystemStats reads Btrfs statistics for a filesystem.
+func (r *reader) readFilesystemStats() (s *Stats) {
+        // First get disk info, and add it to reader
+        devices := r.readDeviceInfo("devices")
+        r.devCount = len(devices)
+
+        s = &Stats{
+                // Read basic filesystem information
+                Label:          r.readFile("label"),
+                UUID:           r.readFile("metadata_uuid"),
+                Features:       r.listFiles("features"),
+                CloneAlignment: r.readValue("clone_alignment"),
+                NodeSize:       r.readValue("nodesize"),
+                QuotaOverride:  r.readValue("quota_override"),
+                SectorSize:     r.readValue("sectorsize"),
+
+                // Device info
+                Devices: devices,
+
+                // Read allocation data
+                Allocation: Allocation{
+                        GlobalRsvReserved: r.readValue("allocation/global_rsv_reserved"),
+                        GlobalRsvSize:     r.readValue("allocation/global_rsv_size"),
+                        Data:              r.readAllocationStats("allocation/data"),
+                        Metadata:          r.readAllocationStats("allocation/metadata"),
+                        System:            r.readAllocationStats("allocation/system"),
+                },
+        }
+        return
+}
diff --git a/vendor/modules.txt b/vendor/modules.txt
index ae4fb57..9b77b1a 100644
--- a/vendor/modules.txt
+++ b/vendor/modules.txt
@@ -62,6 +62,7 @@ github.com/prometheus/common/version
 # github.com/prometheus/procfs v0.0.10
 github.com/prometheus/procfs
 github.com/prometheus/procfs/bcache
+github.com/prometheus/procfs/btrfs
 github.com/prometheus/procfs/internal/fs
 github.com/prometheus/procfs/internal/util
 github.com/prometheus/procfs/nfs