ublk: document zero copy feature

Add words to explain how zero copy feature works, and why it has to be
trusted for handling IO read command.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250327095123.179113-8-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

ublk: add segment parameter

IO split is usually bad in io_uring world, since -EAGAIN is caused and
IO handling may have to fallback to io-wq, this way does hurt performance.

ublk starts to support zero copy recently, for avoiding unnecessary IO
split, ublk driver's segment limit should be aligned with backend
device's segment limit.

Another reason is that io_buffer_register_bvec() needs to allocate bvecs,
which number is aligned with ublk request segment number, so that big
memory allocation can be avoided by setting reasonable max_segments limit.

So add segment parameter for providing ublk server chance to align
segment limit with backend, and keep it reasonable from implementation
viewpoint.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250327095123.179113-7-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

ublk: call io_uring_cmd_to_pdu to get uring_cmd pdu

Call io_uring_cmd_to_pdu() to get uring_cmd pdu, and one big benefit
is the automatic pdu size build check.

Suggested-by: Uday Shankar <ushankar@purestorage.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Caleb Sander Mateos <csander@purestorage.com>
Link: https://lore.kernel.org/r/20250327095123.179113-6-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

ublk: add helper of ublk_need_map_io()

ublk_need_map_io() is more readable.

Reviewed-by: Caleb Sander Mateos <csander@purestorage.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250327095123.179113-5-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

ublk: remove two unused fields from 'struct ublk_queue'

Remove two unused fields(`io_addr` & `max_io_sz`) from `struct ublk_queue`.

Reviewed-by: Caleb Sander Mateos <csander@purestorage.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250327095123.179113-4-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

ublk: comment on ubq->canceling handling in ublk_queue_rq()

In ublk_queue_rq(), ubq->canceling has to be handled after ->fail_io and
->force_abort are dealt with, otherwise the request may not be failed
when deleting disk.

Add comment on this usage.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250327095123.179113-3-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

ublk: make sure ubq->canceling is set when queue is frozen

Now ublk driver depends on `ubq->canceling` for deciding if the request
can be dispatched via uring_cmd & io_uring_cmd_complete_in_task().

Once ubq->canceling is set, the uring_cmd can be done via ublk_cancel_cmd()
and io_uring_cmd_done().

So set ubq->canceling when queue is frozen, this way makes sure that the
flag can be observed from ublk_queue_rq() reliably, and avoids
use-after-free on uring_cmd.

Fixes: 216c8f5ef0f2 ("ublk: replace monitor with cancelable uring_cmd")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250327095123.179113-2-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/net: account memory for zc sendmsg

Account pinned pages for IORING_OP_SENDMSG_ZC, just as we for
IORING_OP_SEND_ZC and net/ does for MSG_ZEROCOPY.

Fixes: 493108d95f146 ("io_uring/net: zerocopy sendmsg")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/4f00f67ca6ac8e8ed62343ae92b5816b1e0c9c4b.1743086313.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>