9956: Load volume config from YAML file

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

diff --git a/services/keepstore/volume.go b/services/keepstore/volume.go
index 58710c04b269a57af236fbb36f5a6aaa61d9b256..6e01e75b879b339232603d38f93cb040ecc6d86c 100644 (file)
--- 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
 
@@ -204,6 +212,17 @@ 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 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