5cc915c26c
This function is not called during plugin initialization (#2140), but should be useful for downstream projects that uses overlayfs snapshotter as a Go library. Benchmark result on Ubuntu 17.10, GCE n1-standard-4: BenchmarkOverlaySupportedOnExt4-4 100 20490598 ns/op BenchmarkOverlayUnsupportedOnFType0XFS-4 30000 39316 ns/op BenchmarkOverlaySupportedOnFType1XFS-4 100 19287083 ns/op BenchmarkOverlayUnsupportedOnFAT-4 100 14217772 ns/op i.e. the overhead is typically about 20 msec on this machine. Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>
89 lines
2.8 KiB
Go
89 lines
2.8 KiB
Go
// +build linux
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/*
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Copyright The containerd Authors.
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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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http://www.apache.org/licenses/LICENSE-2.0
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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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*/
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package overlay
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import (
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"fmt"
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"io/ioutil"
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"os"
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"path/filepath"
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"github.com/containerd/containerd/log"
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"github.com/containerd/containerd/mount"
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"github.com/containerd/continuity/fs"
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"github.com/pkg/errors"
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)
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// supportsMultipleLowerDir checks if the system supports multiple lowerdirs,
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// which is required for the overlay snapshotter. On 4.x kernels, multiple lowerdirs
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// are always available (so this check isn't needed), and backported to RHEL and
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// CentOS 3.x kernels (3.10.0-693.el7.x86_64 and up). This function is to detect
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// support on those kernels, without doing a kernel version compare.
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//
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// Ported from moby overlay2.
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func supportsMultipleLowerDir(d string) error {
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td, err := ioutil.TempDir(d, "multiple-lowerdir-check")
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if err != nil {
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return err
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}
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defer func() {
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if err := os.RemoveAll(td); err != nil {
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log.L.WithError(err).Warnf("Failed to remove check directory %v", td)
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}
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}()
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for _, dir := range []string{"lower1", "lower2", "upper", "work", "merged"} {
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if err := os.Mkdir(filepath.Join(td, dir), 0755); err != nil {
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return err
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}
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}
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opts := fmt.Sprintf("lowerdir=%s:%s,upperdir=%s,workdir=%s", filepath.Join(td, "lower2"), filepath.Join(td, "lower1"), filepath.Join(td, "upper"), filepath.Join(td, "work"))
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m := mount.Mount{
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Type: "overlay",
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Source: "overlay",
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Options: []string{opts},
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}
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dest := filepath.Join(td, "merged")
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if err := m.Mount(dest); err != nil {
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return errors.Wrap(err, "failed to mount overlay")
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}
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if err := mount.UnmountAll(dest, 0); err != nil {
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log.L.WithError(err).Warnf("Failed to unmount check directory %v", dest)
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}
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return nil
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}
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// Supported returns nil when the overlayfs is functional on the system with the root directory.
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// Suppported is not called during plugin initialization, but exposed for downstream projects which uses
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// this snapshotter as a library.
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func Supported(root string) error {
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if err := os.MkdirAll(root, 0700); err != nil {
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return err
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}
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supportsDType, err := fs.SupportsDType(root)
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if err != nil {
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return err
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}
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if !supportsDType {
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return fmt.Errorf("%s does not support d_type. If the backing filesystem is xfs, please reformat with ftype=1 to enable d_type support", root)
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}
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return supportsMultipleLowerDir(root)
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}
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