You only fill the bytes that you want to to set explicitly:

+       put_unaligned_le16(0x0002,  &sctpg[0]); /* SCT_ACT_WRITE_SAME */
+       put_unaligned_le16(0x0101,  &sctpg[1]); /* WRITE PTRN FG */
+       put_unaligned_le64(lba,     &sctpg[2]);
+       put_unaligned_le64(num,     &sctpg[6]);
+       put_unaligned_le32(0u,      &sctpg[10]);

What I doubted is, if you don't memset (zero-fill) the buffer first,
will other bytes have indeterministic value that causes random
unexpected behavior?

On 25 August 2016 at 06:04, Shaun Tancheff [off-list ref] wrote:

On Wed, Aug 24, 2016 at 1:10 AM, Tom Yan [off-list ref] wrote:

quoted

Btw, I wonder if you need to memset your buffer with 0 first, like
what is done in ata_scsi_rbuf_get.

It is not necessary as the defined buffer is completely filled out here.

Are you thinking as a sort of future proofing?
Ex: In the unlikely event that the SCT Write Same command
descriptor is expanded in a future ACS?

It is more likely to see the command deprecated and replaced with a
new SCT feature.

Regardless of how unlikely I would consider a memset here to clear
the remainder of the payload.