X-Git-Url: https://git.arvados.org/arvados.git/blobdiff_plain/0bd1c28bed9a0756c61037947d5a9dccd5066f00..d4c8504da527f1a984ecd1ed0da7147010f38b6e:/services/keepstore/handlers.go?ds=sidebyside

diff --git a/services/keepstore/handlers.go b/services/keepstore/handlers.go
index 9838694ac8..039b2ac9a3 100644
--- a/services/keepstore/handlers.go
+++ b/services/keepstore/handlers.go
@@ -148,7 +148,7 @@ func GetBlockHandler(resp http.ResponseWriter, req *http.Request) {
 		}
 	}
 
-	block, err := GetBlock(hash)
+	block, err := GetBlock(hash, false)
 
 	// Garbage collect after each GET. Fixes #2865.
 	// TODO(twp): review Keep memory usage and see if there's
@@ -397,7 +397,34 @@ func DeleteHandler(resp http.ResponseWriter, req *http.Request) {
 	}
 }
 
-func GetBlock(hash string) ([]byte, error) {
+// ==============================
+// GetBlock and PutBlock implement lower-level code for handling
+// blocks by rooting through volumes connected to the local machine.
+// Once the handler has determined that system policy permits the
+// request, it calls these methods to perform the actual operation.
+//
+// TODO(twp): this code would probably be better located in the
+// VolumeManager interface. As an abstraction, the VolumeManager
+// should be the only part of the code that cares about which volume a
+// block is stored on, so it should be responsible for figuring out
+// which volume to check for fetching blocks, storing blocks, etc.
+
+// ==============================
+// GetBlock fetches and returns the block identified by "hash".  If
+// the update_timestamp argument is true, GetBlock also updates the
+// block's file modification time (for the sake of PutBlock, which
+// must update the file's timestamp when the block already exists).
+//
+// On success, GetBlock returns a byte slice with the block data, and
+// a nil error.
+//
+// If the block cannot be found on any volume, returns NotFoundError.
+//
+// If the block found does not have the correct MD5 hash, returns
+// DiskHashError.
+//
+
+func GetBlock(hash string, update_timestamp bool) ([]byte, error) {
 	// Attempt to read the requested hash from a keep volume.
 	error_to_caller := NotFoundError
 
@@ -432,6 +459,14 @@ func GetBlock(hash string) ([]byte, error) {
 					log.Printf("%s: checksum mismatch for request %s but a good copy was found on another volume and returned\n",
 						vol, hash)
 				}
+				// Update the timestamp if the caller requested.
+				// If we could not update the timestamp, continue looking on
+				// other volumes.
+				if update_timestamp {
+					if vol.Touch(hash) != nil {
+						continue
+					}
+				}
 				return buf, nil
 			}
 		}
@@ -478,12 +513,15 @@ func PutBlock(block []byte, hash string) error {
 	}
 
 	// If we already have a block on disk under this identifier, return
-	// success (but check for MD5 collisions).
+	// success (but check for MD5 collisions).  While fetching the block,
+	// update its timestamp.
 	// The only errors that GetBlock can return are DiskHashError and NotFoundError.
 	// In either case, we want to write our new (good) block to disk,
 	// so there is nothing special to do if err != nil.
-	if oldblock, err := GetBlock(hash); err == nil {
+	//
+	if oldblock, err := GetBlock(hash, true); err == nil {
 		if bytes.Compare(block, oldblock) == 0 {
+			// The block already exists; return success.
 			return nil
 		} else {
 			return CollisionError