-type BlockWriter interface {
- // WriteBlock reads all data from r, writes it to a backing
- // store as "loc", and returns the number of bytes written.
- WriteBlock(ctx context.Context, loc string, r io.Reader) error
-}
-
-type BlockReader interface {
- // ReadBlock retrieves data previously stored as "loc" and
- // writes it to w.
- ReadBlock(ctx context.Context, loc string, w io.Writer) error
-}
-
-var driver = map[string]func(*arvados.Cluster, arvados.Volume, logrus.FieldLogger, *volumeMetricsVecs) (Volume, error){}
-
-// A Volume is an interface representing a Keep back-end storage unit:
-// for example, a single mounted disk, a RAID array, an Amazon S3 volume,
-// etc.
-type Volume interface {
- // 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 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
- // retrieving the data, that error should be returned so the
- // caller can log (and send to the client) a more useful
- // message.
- //
- // If the error is "not found", and there's no particular
- // reason to expect the block to be found (other than that a
- // caller is asking for it), the returned error should satisfy
- // os.IsNotExist(err): this is a normal condition and will not
- // be logged as an error (except that a 404 will appear in the
- // access log if the block is not found on any other volumes
- // either).
- //
- // 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(ctx context.Context, 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
- // CollisionError or DiskHashError (depending on whether the
- // data on disk matches the expected hash), or whatever error
- // was encountered opening/reading the stored data.
- Compare(ctx context.Context, loc string, data []byte) error
-
- // Put writes a block to an underlying storage device.
- //
- // loc is as described in Get.
- //
- // len(block) is guaranteed to be between 0 and BlockSize.
- //
- // If a block is already stored under the same name (loc) with
- // different content, Put must either overwrite the existing
- // data with the new data or return a non-nil error. When
- // overwriting existing data, it must never leave the storage
- // device in an inconsistent state: a subsequent call to Get
- // must return either the entire old block, the entire new
- // block, or an error. (An implementation that cannot peform
- // atomic updates must leave the old data alone and return an
- // error.)
- //
- // Put also sets the timestamp for the given locator to the
- // current time.
- //
- // Put must return a non-nil error unless it can guarantee
- // that the entire block has been written and flushed to
- // persistent storage, and that its timestamp is current. Of
- // course, this guarantee is only as good as the underlying
- // storage device, but it is Put's responsibility to at least
- // get whatever guarantee is offered by the storage device.
- //
- // Put should not verify that loc==hash(block): this is the
- // caller's responsibility.
- Put(ctx context.Context, loc string, block []byte) error
-
- // Touch sets the timestamp for the given locator to the
- // current time.
- //
- // loc is as described in Get.
- //
- // If invoked at time t0, Touch must guarantee that a
- // subsequent call to Mtime will return a timestamp no older
- // than {t0 minus one second}. For example, if Touch is called
- // at 2015-07-07T01:23:45.67890123Z, it is acceptable for a
- // subsequent Mtime to return any of the following:
- //
- // - 2015-07-07T01:23:45.00000000Z
- // - 2015-07-07T01:23:45.67890123Z
- // - 2015-07-07T01:23:46.67890123Z
- // - 2015-07-08T00:00:00.00000000Z
- //
- // It is not acceptable for a subsequente Mtime to return
- // either of the following:
- //
- // - 2015-07-07T00:00:00.00000000Z -- ERROR
- // - 2015-07-07T01:23:44.00000000Z -- ERROR
- //
- // Touch must return a non-nil error if the timestamp cannot
- // be updated.
- Touch(loc string) error
-
- // Mtime returns the stored timestamp for the given locator.
- //
- // loc is as described in Get.
- //
- // Mtime must return a non-nil error if the given block is not
- // found or the timestamp could not be retrieved.
- Mtime(loc string) (time.Time, error)
-
- // IndexTo writes a complete list of locators with the given
- // prefix for which Get() can retrieve data.
- //
- // prefix consists of zero or more lowercase hexadecimal
- // digits.
- //
- // Each locator must be written to the given writer using the
- // following format:
- //
- // loc "+" size " " timestamp "\n"
- //
- // where:
- //
- // - size is the number of bytes of content, given as a
- // decimal number with one or more digits
- //
- // - timestamp is the timestamp stored for the locator,
- // given as a decimal number of seconds after January 1,
- // 1970 UTC.
- //
- // IndexTo must not write any other data to writer: for
- // example, it must not write any blank lines.
- //
- // If an error makes it impossible to provide a complete
- // index, IndexTo must return a non-nil error. It is
- // acceptable to return a non-nil error after writing a
- // partial index to writer.
- //
- // The resulting index is not expected to be sorted in any
- // particular order.
- IndexTo(prefix string, writer io.Writer) error
-
- // Trash moves the block data from the underlying storage
- // device to trash area. The block then stays in trash for
- // BlobTrashLifetime before it is actually deleted.
- //
- // loc is as described in Get.
- //
- // If the timestamp for the given locator is newer than
- // BlobSigningTTL, Trash must not trash the data.
- //
- // 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
- // - Trash does not trash the block, or
- // - Both of the above.
- //
- // If it is possible for the storage device to be accessed by
- // a different process or host, the synchronization mechanism
- // should also guard against races with other processes and
- // hosts. If such a mechanism is not available, there must be
- // a mechanism for detecting unsafe configurations, alerting
- // the operator, and aborting or falling back to a read-only
- // state. In other words, running multiple keepstore processes
- // with the same underlying storage device must either work
- // reliably or fail outright.
- //
- // Corollary: A successful Touch or Put guarantees a block
- // will not be trashed for at least BlobSigningTTL seconds.
- 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
- // implementation-specific volume identifier (e.g., "mount
- // point" for a UnixVolume).
- Status() *VolumeStatus
-
- // String returns an identifying label for this volume,
- // suitable for including in log messages. It should contain
- // enough information to uniquely identify the underlying
- // storage device, but should not contain any credentials or
- // secrets.
- String() string
-
- // EmptyTrash looks for trashed blocks that exceeded
- // BlobTrashLifetime and deletes them from the volume.