Merge branch 'master' into 9369-arv-cwl-docs

[arvados.git] / services / keepstore / volume.go

diff --git a/services/keepstore/volume.go b/services/keepstore/volume.go
index 7966c41b92bd89958308ec77765f0b7a5a1f0fd9..8ae6660fd477fa90365a019c837a121a08cc9595 100644 (file)
--- a/services/keepstore/volume.go
+++ b/services/keepstore/volume.go
@@ -10,17 +10,14 @@ import (
 // for example, a single mounted disk, a RAID array, an Amazon S3 volume,
 // etc.
 type Volume interface {
-       // Get a block. IFF the returned error is nil, the caller must
-       // put the returned slice back into the buffer pool when it's
-       // finished with it. (Otherwise, the buffer pool will be
-       // depleted and eventually -- when all available buffers are
-       // used and not returned -- operations will reach deadlock.)
+       // Get a block: copy the block data into buf, and return the
+       // number of bytes copied.
        //
        // loc is guaranteed to consist of 32 or more lowercase hex
        // digits.
        //
-       // Get should not verify the integrity of the returned data:
-       // it should just return whatever was found in its backing
+       // Get should not verify the integrity of the data: it should
+       // just return whatever was found in its backing
        // store. (Integrity checking is the caller's responsibility.)
        //
        // If an error is encountered that prevents it from
@@ -36,10 +33,12 @@ type Volume interface {
        // access log if the block is not found on any other volumes
        // either).
        //
-       // If the data in the backing store is bigger than BlockSize,
-       // Get is permitted to return an error without reading any of
-       // the data.
-       Get(loc string) ([]byte, error)
+       // If the data in the backing store is bigger than len(buf),
+       // then Get is permitted to return an error without reading
+       // any of the data.
+       //
+       // len(buf) will not exceed BlockSize.
+       Get(loc string, buf []byte) (int, error)
 
        // Compare the given data with the stored data (i.e., what Get
        // would return). If equal, return nil. If not, return
@@ -144,20 +143,21 @@ type Volume interface {
        // particular order.
        IndexTo(prefix string, writer io.Writer) error
 
-       // Delete deletes the block data from the underlying storage
-       // device.
+       // Trash moves the block data from the underlying storage
+       // device to trash area. The block then stays in trash for
+       // -trash-lifetime interval before it is actually deleted.
        //
        // loc is as described in Get.
        //
        // If the timestamp for the given locator is newer than
-       // blobSignatureTTL, Delete must not delete the data.
+       // blobSignatureTTL, Trash must not trash the data.
        //
-       // If a Delete operation overlaps with any Touch or Put
+       // If a Trash operation overlaps with any Touch or Put
        // operations on the same locator, the implementation must
        // ensure one of the following outcomes:
        //
        //   - Touch and Put return a non-nil error, or
-       //   - Delete does not delete the block, or
+       //   - Trash does not trash the block, or
        //   - Both of the above.
        //
        // If it is possible for the storage device to be accessed by
@@ -171,9 +171,12 @@ type Volume interface {
        // reliably or fail outright.
        //
        // Corollary: A successful Touch or Put guarantees a block
-       // will not be deleted for at least blobSignatureTTL
+       // will not be trashed for at least blobSignatureTTL
        // seconds.
-       Delete(loc string) error
+       Trash(loc string) error
+
+       // Untrash moves block from trash back into store
+       Untrash(loc string) error
 
        // Status returns a *VolumeStatus representing the current
        // in-use and available storage capacity and an
@@ -200,6 +203,10 @@ type Volume interface {
        // underlying device. It will be passed on to clients in
        // responses to PUT requests.
        Replication() int
+
+       // EmptyTrash looks for trashed blocks that exceeded trashLifetime
+       // and deletes them from the volume.
+       EmptyTrash()
 }
 
 // A VolumeManager tells callers which volumes can read, which volumes