Re: [PATCH v2] block: only read from sqe on initial invocation of blkdev_uring_cmd()

[Jens Axboe <axboe@kernel.dk>]

On 5/5/26 9:32 AM, Caleb Sander Mateos wrote:
> On Tue, May 5, 2026 at 12:38?AM Jens Axboe <axboe@kernel.dk> wrote:
>>
>> This passthrough helper currently only supports discards. Part of that
>> command is the start and length, which is read from the SQE. It does
>> so on every invocation, where it really should just make it stable
>> on the first invocation. This avoids needing to copy the SQE upfront,
>> as we only really need those two 8b values stored in our per-req
>> payload.
> 
> Maybe I'm missing something, but how does this avoid the SQE copy?
> Won't io_uring_cmd_sqe_copy() still copy the SQE if the command issue
> is delayed by links/drain/forced async or if the initial issue returns
> EAGAIN? The code change looks fine to me, but I'm not sure I
> understand the motivation.

Because the alternative would be to copy it upfront and then using ->sqe
would always be fine. But we can just ensure start/len are stable. The
patch is about the latter, not adding any further copy avoidance. Yes if
you use async or it's a link or drained, prep will always copy it.
That's fine.

-- 
Jens Axboe