Issue

We have found that some storage arrays at some firmware revisions return errors on WRITE SAME commands issued to perform discard operations. A new blacklist flag allows the kernel to avoid issuing commands that the array will incorrectly reject.

From the patch description:

Implement blacklist option for WRITE SAME w/ UNMAP

SBC-4 states:
  "A MAXIMUM UNMAP LBA COUNT field set to a non-zero value indicates the
   maximum number of LBAs that may be unmapped by an UNMAP command"

  "A MAXIMUM WRITE SAME LENGTH field set to a non-zero value indicates
   the maximum number of contiguous logical blocks that the device server
   allows to be unmapped or written in a single WRITE SAME command."

Despite the spec being clear on the topic, some devices incorrectly
expect WRITE SAME commands with the UNMAP bit set to be limited to the
value reported in MAXIMUM UNMAP LBA COUNT in the Block Limits VPD.

Implement a blacklist option that can be used to accommodate devices
with this behavior.