Re: [PATCH v6 2/4] Add support for SCT Write Same

Tom Yan
2016-08-25T06:40:43Z

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 <shaun@tancheff.com> wrote:
> On Wed, Aug 24, 2016 at 1:10 AM, Tom Yan <tom.ty89@gmail.com> wrote:
>> 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.