Add Btrfs collector (#1512)

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

Resolves #1100

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

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
+}