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snapshot: replace "readonly" with View snapshot type

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What started out as a simple PR to remove the "Readonly" column became an
adventure to add a proper type for a "View" snapshot. The short story here is
that we now get the following output:

```
$ sudo ctr snapshot ls
ID 									 PARENT 								 KIND
sha256:08c2295a7fa5c220b0f60c994362d290429ad92f6e0235509db91582809442f3 								  	 Committed
testing4								 sha256:08c2295a7fa5c220b0f60c994362d290429ad92f6e0235509db91582809442f3 Active
```

In pursuing this output, it was found that the idea of having "readonly" as an
attribute on all snapshots was redundant. For committed, they are always
readonly, as they are not accessible without an active snapshot. For active
snapshots that were views, we'd have to check the type before interpreting
"readonly". With this PR, this is baked fully into the kind of snapshot. When
`Snapshotter.View` is  called, the kind of snapshot is `KindView`, and the
storage system reflects this end to end.

Unfortunately, this will break existing users. There is no migration, so they
will have to wipe `/var/lib/containerd` and recreate everything. However, this
is deemed worthwhile at this point, as we won't have to judge validity of the
"Readonly" field when new snapshot types are added.

Signed-off-by: Stephen J Day <stephen.day@docker.com>
This commit is contained in:
Stephen J Day
2017-07-21 17:49:30 -07:00
parent a9ab45fb77
commit 863784f991
17 changed files with 396 additions and 444 deletions
Download Patch File Download Diff File Expand all files Collapse all files

47
snapshot/btrfs/btrfs.go
View File

@@ -7,6 +7,7 @@ import (
"fmt"
"os"
"path/filepath"
"strings"
"github.com/containerd/btrfs"
"github.com/containerd/containerd/log"
@@ -58,11 +59,13 @@ func NewSnapshotter(root string) (snapshot.Snapshotter, error) {
}
var (
active = filepath.Join(root, "active")
view = filepath.Join(root, "view")
snapshots = filepath.Join(root, "snapshots")
)
for _, path := range []string{
active,
view,
snapshots,
} {
if err := os.Mkdir(path, 0755); err != nil && !os.IsExist(err) {
@@ -127,14 +130,14 @@ func (b *snapshotter) Walk(ctx context.Context, fn func(context.Context, snapsho
}
func (b *snapshotter) Prepare(ctx context.Context, key, parent string) ([]mount.Mount, error) {
return b.makeActive(ctx, key, parent, false)
return b.makeSnapshot(ctx, snapshot.KindActive, key, parent)
}
func (b *snapshotter) View(ctx context.Context, key, parent string) ([]mount.Mount, error) {
return b.makeActive(ctx, key, parent, true)
return b.makeSnapshot(ctx, snapshot.KindView, key, parent)
}
func (b *snapshotter) makeActive(ctx context.Context, key, parent string, readonly bool) ([]mount.Mount, error) {
func (b *snapshotter) makeSnapshot(ctx context.Context, kind snapshot.Kind, key, parent string) ([]mount.Mount, error) {
ctx, t, err := b.ms.TransactionContext(ctx, true)
if err != nil {
return nil, err
@@ -147,23 +150,29 @@ func (b *snapshotter) makeActive(ctx context.Context, key, parent string, readon
}
}()
a, err := storage.CreateActive(ctx, key, parent, readonly)
s, err := storage.CreateSnapshot(ctx, kind, key, parent)
if err != nil {
return nil, err
}
target := filepath.Join(b.root, "active", a.ID)
target := filepath.Join(b.root, strings.ToLower(s.Kind.String()), s.ID)
if len(a.ParentIDs) == 0 {
if len(s.ParentIDs) == 0 {
// create new subvolume
// btrfs subvolume create /dir
if err = btrfs.SubvolCreate(target); err != nil {
return nil, err
}
} else {
parentp := filepath.Join(b.root, "snapshots", a.ParentIDs[0])
parentp := filepath.Join(b.root, "snapshots", s.ParentIDs[0])
var readonly bool
if kind == snapshot.KindView {
readonly = true
}
// btrfs subvolume snapshot /parent /subvol
if err = btrfs.SubvolSnapshot(target, parentp, a.Readonly); err != nil {
if err = btrfs.SubvolSnapshot(target, parentp, readonly); err != nil {
return nil, err
}
}
@@ -256,12 +265,13 @@ func (b *snapshotter) Mounts(ctx context.Context, key string) ([]mount.Mount, er
if err != nil {
return nil, err
}
a, err := storage.GetActive(ctx, key)
s, err := storage.GetSnapshot(ctx, key)
t.Rollback()
if err != nil {
return nil, errors.Wrap(err, "failed to get active snapshot")
}
dir := filepath.Join(b.root, "active", a.ID)
dir := filepath.Join(b.root, strings.ToLower(s.Kind.String()), s.ID)
return b.mounts(dir)
}
@@ -296,18 +306,15 @@ func (b *snapshotter) Remove(ctx context.Context, key string) (err error) {
return errors.Wrap(err, "failed to remove snapshot")
}
if k == snapshot.KindActive {
switch k {
case snapshot.KindView:
source = filepath.Join(b.root, "view", id)
removed = filepath.Join(b.root, "view", "rm-"+id)
readonly = true
case snapshot.KindActive:
source = filepath.Join(b.root, "active", id)
info, err := btrfs.SubvolInfo(source)
if err != nil {
source = ""
return err
}
readonly = info.Readonly
removed = filepath.Join(b.root, "active", "rm-"+id)
} else {
case snapshot.KindCommitted:
source = filepath.Join(b.root, "snapshots", id)
removed = filepath.Join(b.root, "snapshots", "rm-"+id)
readonly = true