9068: Move buffer allocation from volumes to GetBlockHandler.

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

diff --git a/services/keepstore/volume.go b/services/keepstore/volume.go
index 17da54fdadbca571cae93fde18342d2776b4e3a7..8ae6660fd477fa90365a019c837a121a08cc9595 100644 (file)
--- a/services/keepstore/volume.go
+++ b/services/keepstore/volume.go
@@ -10,17 +10,14 @@ 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.)
+       // 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 +33,12 @@ 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