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snapshot: add Usage method to Snapshotter

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To allow the querying of usage for snapshots, we define a new method on
the snapshotter to query the resources in use by a single snapshot.
Conversely, it can be said that if the snapshot was deleted, the
reported amount of usage would be recovered.

There are few problems with this model in the implementation of btrfs
that need to be worked out. In btrfs, it is hard to resolve the amount
of data usage with the use of quotas but these may report valuables that
are incompatible with the model.

Signed-off-by: Stephen J Day <stephen.day@docker.com>
This commit is contained in:
Stephen J Day
2017-04-12 17:56:04 -07:00
parent 4a749ad473
commit 66c504d1bb
13 changed files with 367 additions and 51 deletions
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25
snapshot/btrfs/btrfs.go
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@@ -88,7 +88,28 @@ func (b *snapshotter) Stat(ctx context.Context, key string) (snapshot.Info, erro
return snapshot.Info{}, err
}
defer t.Rollback()
return storage.GetInfo(ctx, key)
_, info, _, err := storage.GetInfo(ctx, key)
if err != nil {
return snapshot.Info{}, err
}
return info, nil
}
// Usage retrieves the disk usage of the top-level snapshot.
func (b *snapshotter) Usage(ctx context.Context, key string) (snapshot.Usage, error) {
panic("not implemented")
// TODO(stevvooe): Btrfs has a quota model where data can be exclusive to a
// snapshot or shared among other resources. We may find that this is the
// correct value to reoprt but the stability of the implementation is under
// question.
//
// In general, this has impact on the model we choose for reporting usage.
// Ideally, the value should allow aggregration. For overlay, this is
// simple since we can scan the diff directory to get a unique value. This
// breaks down when start looking the behavior when data is shared between
// snapshots, such as that for btrfs.
}
// Walk the committed snapshots.
@@ -193,7 +214,7 @@ func (b *snapshotter) Commit(ctx context.Context, name, key string) (err error)
}
}()
id, err := storage.CommitActive(ctx, key, name)
id, err := storage.CommitActive(ctx, key, name, snapshot.Usage{}) // TODO(stevvooe): Resolve a usage value for btrfs
if err != nil {
return errors.Wrap(err, "failed to commit")
}