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fs: introduce pluggable filesystem architecture
This change replaces hardcoded filesystem type handling in fs/fs.go with a pluggable system where each filesystem type is handled by a dedicated plugin. New plugin interfaces (fs/plugin.go): - FsPlugin: core interface for filesystem stats and mount processing - FsCachingPlugin: optional interface for plugins that cache stats by device ID (e.g., NFS with multiple mounts to same device) - FsWatcherPlugin: optional interface for background monitoring (e.g., ZFS watcher, ThinPool watcher) Filesystem plugins implemented: - fs/vfs: handles ext2/3/4, xfs, and standard block filesystems - fs/zfs: ZFS with optional watcher for container-level usage - fs/devicemapper: DeviceMapper thin pool support - fs/btrfs: btrfs with major/minor ID correction - fs/overlay: overlay with source uniqueness via device ID - fs/nfs: NFS with device-based caching - fs/tmpfs: tmpfs with per-mount tracking Signed-off-by: Davanum Srinivas <davanum@gmail.com>
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‎cmd/internal/container/install/install.go‎

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@@ -22,4 +22,13 @@ import (
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_ "github.com/google/cadvisor/container/docker/install"
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_ "github.com/google/cadvisor/container/podman/install"
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_ "github.com/google/cadvisor/container/systemd/install"
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// Register all filesystem plugins.
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_ "github.com/google/cadvisor/fs/btrfs/install"
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_ "github.com/google/cadvisor/fs/devicemapper/install"
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_ "github.com/google/cadvisor/fs/nfs/install"
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_ "github.com/google/cadvisor/fs/overlay/install"
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_ "github.com/google/cadvisor/fs/tmpfs/install"
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_ "github.com/google/cadvisor/fs/vfs/install"
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_ "github.com/google/cadvisor/fs/zfs/install"
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)

‎fs/btrfs/install/install.go‎

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// Copyright 2014 Google Inc. All Rights Reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package install
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import (
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"github.com/google/cadvisor/fs"
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"github.com/google/cadvisor/fs/btrfs"
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"k8s.io/klog/v2"
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)
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func init() {
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err := fs.RegisterPlugin("btrfs", btrfs.NewPlugin())
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if err != nil {
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klog.Fatalf("Failed to register btrfs fs plugin: %v", err)
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}
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}

‎fs/btrfs/mount.go‎

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// Copyright 2014 Google Inc. All Rights Reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//go:build linux
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package btrfs
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import (
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"fmt"
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"syscall"
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mount "github.com/moby/sys/mountinfo"
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"k8s.io/klog/v2"
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)
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// major extracts the major device number from a device number.
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func major(devNumber uint64) uint {
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return uint((devNumber >> 8) & 0xfff)
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}
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// minor extracts the minor device number from a device number.
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func minor(devNumber uint64) uint {
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return uint((devNumber & 0xff) | ((devNumber >> 12) & 0xfff00))
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}
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// GetBtrfsMajorMinorIds gets the major and minor device IDs for a btrfs mount point.
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// This is a workaround for wrong btrfs Major and Minor Ids reported in /proc/self/mountinfo.
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// Instead of using values from /proc/self/mountinfo we use stat to get Ids from btrfs mount point.
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func GetBtrfsMajorMinorIds(mnt *mount.Info) (int, int, error) {
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buf := new(syscall.Stat_t)
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err := syscall.Stat(mnt.Source, buf)
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if err != nil {
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err = fmt.Errorf("stat failed on %s with error: %s", mnt.Source, err)
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return 0, 0, err
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}
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klog.V(4).Infof("btrfs mount %#v", mnt)
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if buf.Mode&syscall.S_IFMT == syscall.S_IFBLK {
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err := syscall.Stat(mnt.Mountpoint, buf)
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if err != nil {
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err = fmt.Errorf("stat failed on %s with error: %s", mnt.Mountpoint, err)
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return 0, 0, err
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}
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// The type Dev and Rdev in Stat_t are 32bit on mips.
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klog.V(4).Infof("btrfs dev major:minor %d:%d\n", int(major(uint64(buf.Dev))), int(minor(uint64(buf.Dev)))) // nolint: unconvert
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klog.V(4).Infof("btrfs rdev major:minor %d:%d\n", int(major(uint64(buf.Rdev))), int(minor(uint64(buf.Rdev)))) // nolint: unconvert
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return int(major(uint64(buf.Dev))), int(minor(uint64(buf.Dev))), nil // nolint: unconvert
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}
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return 0, 0, fmt.Errorf("%s is not a block device", mnt.Source)
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}

‎fs/btrfs/plugin.go‎

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// Copyright 2014 Google Inc. All Rights Reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//go:build linux
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package btrfs
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import (
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"strings"
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"github.com/google/cadvisor/fs"
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"github.com/google/cadvisor/fs/vfs"
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mount "github.com/moby/sys/mountinfo"
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"k8s.io/klog/v2"
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)
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type btrfsPlugin struct{}
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// NewPlugin creates a new Btrfs filesystem plugin.
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func NewPlugin() fs.FsPlugin {
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return &btrfsPlugin{}
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}
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func (p *btrfsPlugin) Name() string {
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return "btrfs"
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}
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// CanHandle returns true if the filesystem type is btrfs.
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func (p *btrfsPlugin) CanHandle(fsType string) bool {
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return fsType == "btrfs"
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}
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// Priority returns 100 - Btrfs has higher priority than VFS.
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func (p *btrfsPlugin) Priority() int {
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return 100
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}
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// GetStats returns filesystem statistics for Btrfs.
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// Btrfs delegates to VFS for stats collection.
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func (p *btrfsPlugin) GetStats(device string, partition fs.PartitionInfo) (*fs.FsStats, error) {
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// Btrfs uses VFS stats
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capacity, free, avail, inodes, inodesFree, err := vfs.GetVfsStats(partition.Mountpoint)
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if err != nil {
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return nil, err
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}
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return &fs.FsStats{
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Capacity: capacity,
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Free: free,
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Available: avail,
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Inodes: &inodes,
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InodesFree: &inodesFree,
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Type: fs.VFS,
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}, nil
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}
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// ProcessMount handles Btrfs mount processing.
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// Btrfs fix: following workaround fixes wrong btrfs Major and Minor Ids reported in /proc/self/mountinfo.
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// Instead of using values from /proc/self/mountinfo we use stat to get Ids from btrfs mount point.
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func (p *btrfsPlugin) ProcessMount(mnt *mount.Info) (bool, *mount.Info, error) {
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// Only apply fix if Major is 0 and Source starts with /dev/
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if mnt.Major == 0 && strings.HasPrefix(mnt.Source, "/dev/") {
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major, minor, err := GetBtrfsMajorMinorIds(mnt)
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if err != nil {
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klog.Warningf("%s", err)
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} else {
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// Create a copy with corrected values
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correctedMnt := *mnt
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correctedMnt.Major = major
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correctedMnt.Minor = minor
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return true, &correctedMnt, nil
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}
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}
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return true, mnt, nil
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}

‎fs/devicemapper/install/install.go‎

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// Copyright 2014 Google Inc. All Rights Reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package install
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import (
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"github.com/google/cadvisor/fs"
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"github.com/google/cadvisor/fs/devicemapper"
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"k8s.io/klog/v2"
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)
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func init() {
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err := fs.RegisterPlugin("devicemapper", devicemapper.NewPlugin())
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if err != nil {
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klog.Fatalf("Failed to register devicemapper fs plugin: %v", err)
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}
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}

‎fs/devicemapper/plugin.go‎

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// Copyright 2014 Google Inc. All Rights Reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package devicemapper
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import (
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"github.com/google/cadvisor/fs"
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mount "github.com/moby/sys/mountinfo"
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"k8s.io/klog/v2"
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)
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type dmPlugin struct{}
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// NewPlugin creates a new DeviceMapper filesystem plugin.
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func NewPlugin() fs.FsPlugin {
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return &dmPlugin{}
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}
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func (p *dmPlugin) Name() string {
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return "devicemapper"
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}
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// CanHandle returns true if the filesystem type is devicemapper.
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func (p *dmPlugin) CanHandle(fsType string) bool {
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return fsType == "devicemapper"
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}
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// Priority returns 100 - DeviceMapper has higher priority than VFS.
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func (p *dmPlugin) Priority() int {
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return 100
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}
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// GetStats returns filesystem statistics for DeviceMapper thin provisioning.
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func (p *dmPlugin) GetStats(device string, partition fs.PartitionInfo) (*fs.FsStats, error) {
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capacity, free, avail, err := GetDMStats(device, partition.BlockSize)
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if err != nil {
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return nil, err
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}
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klog.V(5).Infof("got devicemapper fs capacity stats: capacity: %v free: %v available: %v", capacity, free, avail)
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return &fs.FsStats{
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Capacity: capacity,
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Free: free,
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Available: avail,
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Type: fs.DeviceMapper,
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}, nil
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}
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// ProcessMount handles DeviceMapper mount processing.
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// For DeviceMapper, no special processing is needed.
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func (p *dmPlugin) ProcessMount(mnt *mount.Info) (bool, *mount.Info, error) {
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return true, mnt, nil
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}

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