Saying Y here will enable generic SG (SCSI generic) v4 support
for any block device.

Unlike SG v3 (aka block/scsi_ioctl.c drivers/scsi/sg.c), SG v4
can handle complicated SCSI commands: tagged variable length cdbs
with bidirectional data transfers and generic request/response
protocols (e.g. Task Management Functions and SMP in Serial
Attached SCSI).

This option is required by recent UDEV versions to properly
access device serial numbers, etc.

If unsure, say Y.

source code:

block/bsg.c