X-Git-Url: https://git.arvados.org/arvados.git/blobdiff_plain/06cf38c24519fa21556686545c768429b5af50dc..4e9fd075b8136613e7edbb0465bcb96ccf5b1f45:/services/keepstore/volume.go

diff --git a/services/keepstore/volume.go b/services/keepstore/volume.go
index 17da54fdad..6e01e75b87 100644
--- a/services/keepstore/volume.go
+++ b/services/keepstore/volume.go
@@ -10,17 +10,23 @@ 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.)
+	// Volume type as specified in config file. Examples: "S3",
+	// "Directory".
+	Type() string
+
+	// Do whatever private setup tasks and configuration checks
+	// are needed. Return non-nil if the volume is unusable (e.g.,
+	// invalid config).
+	Start() error
+
+	// 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 +42,12 @@ 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
@@ -151,7 +159,7 @@ type Volume interface {
 	// loc is as described in Get.
 	//
 	// If the timestamp for the given locator is newer than
-	// blobSignatureTTL, Trash must not trash the data.
+	// BlobSignatureTTL, Trash must not trash the data.
 	//
 	// If a Trash operation overlaps with any Touch or Put
 	// operations on the same locator, the implementation must
@@ -172,7 +180,7 @@ type Volume interface {
 	// reliably or fail outright.
 	//
 	// Corollary: A successful Touch or Put guarantees a block
-	// will not be trashed for at least blobSignatureTTL
+	// will not be trashed for at least BlobSignatureTTL
 	// seconds.
 	Trash(loc string) error
 
@@ -205,11 +213,18 @@ type Volume interface {
 	// responses to PUT requests.
 	Replication() int
 
-	// EmptyTrash looks for trashed blocks that exceeded trashLifetime
+	// EmptyTrash looks for trashed blocks that exceeded TrashLifetime
 	// and deletes them from the volume.
 	EmptyTrash()
 }
 
+// A VolumeWithExamples provides example configs to display in the
+// -help message.
+type VolumeWithExamples interface {
+	Volume
+	Examples() []Volume
+}
+
 // A VolumeManager tells callers which volumes can read, which volumes
 // can write, and on which volume the next write should be attempted.
 type VolumeManager interface {