[Drbd-dev] remove REQ_OP_WRITE_SAME

[Martin K. Petersen]

Christoph,

> Now that we are using REQ_OP_WRITE_ZEROES for all zeroing needs in the
> kernel there is very little use left for REQ_OP_WRITE_SAME.  We only
> have two callers left, and both just export optional protocol features
> to remote systems: DRBD and the target code.

While I'm not particularly married to WRITE SAME, I do think it's a
shame that the RAID5/6 code never started using it. It does make a
difference when initializing RAID sets.

The other thing that keeps me a bit on the fence is that a bunch of the
plumbing to handle a bio with a payload different from bi_size is needed
for the copy offload token. I'm hoping to have those patches ready for
4.13. Right now there are a bunch of places where handling of
REQ_OP_COPY_IN and REQ_OP_COPY_OUT share conditionals with WRITE SAME.

So I suggest postponing the decision about whether to rip out WRITE SAME
until I finish the token stuff.

-- 
Martin K. Petersen	Oracle Linux Engineering