rbd: write max 1gb per WriteSame() operation

It seems that writing more than 1 GiB per WriteSame() operation causes
an EINVAL (22) "Invalid argument" error. Splitting the writes in blocks
of maximum 1 GiB should prevent that from happening.

Not all volumes are of a size that is the multiple of the stripe-size.
WriteSame() needs to write full blocks of data, so in case there is a
small left-over, it will be filled with WriteAt().

Signed-off-by: Niels de Vos <ndevos@redhat.com>

internal/rbd/rbd_util.go

@@ -333,15 +333,52 @@ func (rv *rbdVolume) allocate(offset uint64) error {
 		return err
 	}
 
-	// zeroBlock is the stripe-period: size of the object-size multiplied
+	// blockSize is the stripe-period: size of the object-size multiplied
 	// by the stripe-count
-	zeroBlock := make([]byte, sc*(1<<st.Order))
+	blockSize := sc * (1 << st.Order)
+	zeroBlock := make([]byte, blockSize)
 
 	// the actual size of the image as available in the pool, can be
 	// marginally different from the requested image size
-	_, err = image.WriteSame(offset, st.Size-offset, zeroBlock, rados.OpFlagNone)
+	size := st.Size - offset
 
-	return err
+	// In case the remaining space on the volume is smaller than blockSize,
+	// write a partial block with WriteAt() after this loop.
+	for size > blockSize {
+		writeSize := size
+		// write a maximum of 1GB per WriteSame() call
+		if size > helpers.GiB {
+			writeSize = helpers.GiB
+		}
+
+		// round down to the size of a zeroBlock
+		if (writeSize % blockSize) != 0 {
+			writeSize = (writeSize / blockSize) * blockSize
+		}
+
+		_, err = image.WriteSame(offset, writeSize, zeroBlock,
+			rados.OpFlagNone)
+		if err != nil {
+			return fmt.Errorf("failed to allocate %d/%d bytes at "+
+				"offset %d: %w", writeSize, blockSize, offset, err)
+		}
+
+		// write succeeded
+		size -= writeSize
+		offset += writeSize
+	}
+
+	// write the last remaining bytes, in case the image size can not be
+	// written with the optimal blockSize
+	if size != 0 {
+		_, err = image.WriteAt(zeroBlock[:size], int64(offset))
+		if err != nil {
+			return fmt.Errorf("failed to allocate %d bytes at "+
+				"offset %d: %w", size, offset, err)
+		}
+	}
+
+	return nil
 }
 
 // isInUse checks if there is a watcher on the image. It returns true if there