// 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
// 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
// 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
// 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
// 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