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Support simultaneous unpacking of same layer

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Prevent unpack failures due to id collision or the need to
wait for another process to finish unpacking. Always attempt
to unpack a layer and handle collisions on commit. Commit
collisions are easily handled as it could be considered the
same as a successful unpack.

Signed-off-by: Derek McGowan <derek@mcgstyle.net>
This commit is contained in:
Derek McGowan 2017-09-06 14:45:07 -07:00
parent 843b35c9f2
commit 597d0d76ae
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GPG Key ID: F58C5D0A4405ACDB
1 changed files with 22 additions and 2 deletions
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22
rootfs/apply.go
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@ -1,7 +1,10 @@
package rootfs
import (
"crypto/rand"
"encoding/base64"
"fmt"
"time"
"github.com/containerd/containerd/errdefs"
"github.com/containerd/containerd/log"
@ -63,7 +66,7 @@ func ApplyLayer(ctx context.Context, layer Layer, chain []digest.Digest, sn snap
return false, errors.Wrap(err, "failed to stat snapshot")
}
key := fmt.Sprintf("extract %s", chainID)
key := fmt.Sprintf("extract-%s %s", uniquePart(), chainID)
// Prepare snapshot with from parent
mounts, err := sn.Prepare(ctx, key, parent.String())
@ -90,8 +93,25 @@ func ApplyLayer(ctx context.Context, layer Layer, chain []digest.Digest, sn snap
}
if err = sn.Commit(ctx, chainID.String(), key); err != nil {
if !errdefs.IsAlreadyExists(err) {
return false, errors.Wrapf(err, "failed to commit snapshot %s", parent)
}
// Destination already exists, cleanup key and return without error
err = nil
if err := sn.Remove(ctx, key); err != nil {
return false, errors.Wrapf(err, "failed to cleanup aborted apply %s", key)
}
return false, nil
}
return true, nil
}
func uniquePart() string {
t := time.Now()
var b [3]byte
// Ignore read failures, just decreases uniqueness
rand.Read(b[:])
return fmt.Sprintf("%d-%s", t.Nanosecond(), base64.URLEncoding.EncodeToString(b[:]))
}