Currently copy between io request buffer(pages) and userspace buffer is
done inside ublk_map_io() or ublk_unmap_io(). This way performs very
well in case of pre-allocated userspace io buffer.

For dynamically allocated or external userspace backend io buffer,
UBLK_F_NEED_GET_DATA is added for ublk server to provide buffer by one
extra command communication for WRITE request. For READ, userspace
simply provides buffer, but can't know when the buffer is done[1].

Add UBLK_F_USER_COPY by moving io data copy out of kernel by providing
read()/write() on /dev/ublkcN, and simply let ublk server do the io
data copy. This way makes both side cleaner, the cost is that one extra
syscall for copy io data between request and backend buffer.

With UBLK_F_USER_COPY, it actually becomes possible to run per-io zero
copy now, such as, only do zero copy for big size IO, so it can be
thought as one prep patch for supporting zero copy. Meantime zero copy
still needs to expose read()/write() buffer for some corner case, such
as passthrough IO.

[1] READ buffer in UBLK_F_NEED_GET_DATA
https://lore.kernel.org/linux-block/116d8a56-0881-56d3-9bcc-78ff3e1dc4e5@linux.alibaba.com/T/#m23bd4b8634c0a054e6797063167b469949a247bb

ublksrv loop usercopy code:

	https://github.com/ming1/ubdsrv/commits/usercopySigned-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20230519065030.351216-8-ming.lei@redhat.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

Support pread()/pwrite() on ublk char device for reading/writing request
io buffer, so data copy between io request buffer and userspace buffer
can be moved to ublk server from ublk driver. Then UBLK_F_NEED_GET_DATA
becomes not necessary, so ublk server can allocate buffer without one
extra round uring command communication for userspace to provide buffer.

IO buffer can be located by iocb->ki_pos which encodes buffer offset, io
tag and queue id info, and type of iocb->ki_pos is u64, so it is big
enough for holding reasonable queue depth, nr_queues and max io buffer
size.
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20230519065030.351216-7-ming.lei@redhat.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

Add 'offset' to 'struct ublk_map_data', so that ublk_copy_user_pages()
can be used to copy any sub-buffer(linear mapped) of the request.
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20230519065030.351216-6-ming.lei@redhat.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

Add one reference counter into request pdu data, and hold this reference
in the request's lifetime.

Prepare for supporting to move request data copy into userspace, which
needs to copy request data by read()/write() on /dev/ublkcN, so we have
to guarantee that read()/write() is done on one valid/active request,
and that will be enhanced by holding the io request reference in
read()/write().
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20230519065030.351216-5-ming.lei@redhat.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

Clean up ublk_copy_user_pages() by using iov_iter_get_pages2, and code
gets simplified a lot and becomes much more readable than before.
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20230519065030.351216-4-ming.lei@redhat.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

Add one small helper to cleanup io command hanlding code path.
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20230519065030.351216-3-ming.lei@redhat.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

task_work_add() is used from early ublk development stage for handling
request in batch. However, since commit 7d4a9317 ("ublk_drv: don't
forward io commands in reserve order"), we can get similar batch
processing with io_uring_cmd_complete_in_task(), and similar performance
data is observed between task_work_add() and
io_uring_cmd_complete_in_task().

Meantime we can kill one fast code path, which is actually seldom used
given it is common to build ublk driver as module.
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20230519065030.351216-2-ming.lei@redhat.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

Currently both requeues of commands that were already sent to the driver
and flush commands submitted from the flush state machine share the same
requeue_list struct request_queue, despite requeues doing head
insertions and flushes not.  Switch to using two separate lists instead.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Link: https://lore.kernel.org/r/20230519044050.107790-8-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

blk_flush_complete_seq currently queues requests that write data after
a pre-flush from the flush state machine at the head of the queue.
This doesn't really make sense, as the original request bypassed all
queue lists by directly diverting to blk_insert_flush from
blk_mq_submit_bio.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Link: https://lore.kernel.org/r/20230519044050.107790-7-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

Requests with the FUA bit on hardware without FUA support need a post
flush before returning to the caller, but they can still be sent using
the normal I/O path after initializing the flush-related fields and
end I/O handler.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20230519044050.107790-6-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

Send write requests issued by the flush state machine through the normal
I/O submission path including the I/O scheduler (if present) so that I/O
scheduler policies are applied to writes with the FUA flag set.

Separate the I/O scheduler members from the flush members in struct
request since now a request may pass through both an I/O scheduler
and the flush machinery.

Note that the actual flush requests, which have no bio attached to the
request still bypass the I/O schedulers.
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
[hch: rebased]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Link: https://lore.kernel.org/r/20230519044050.107790-5-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

If blk_insert_flush decides that a command does not need to use the
flush state machine, return false and let blk_mq_submit_bio handle
it the normal way (including using an I/O scheduler) instead of doing
a bypass insert.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Link: https://lore.kernel.org/r/20230519044050.107790-4-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

Use a switch statement to decide on the disposition of a flush request
instead of multiple if statements, out of which one does checks that are
more complex than required.  Also warn on a malformed request early
on instead of doing a BUG_ON later.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20230519044050.107790-3-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

Factor out a helper from blk_insert_flush that initializes the flush
machine related fields in struct request, and don't bother with the
full memset as there's just a few fields to initialize, and all but
one already have explicit initializers.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20230519044050.107790-2-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

def_blk_fops always returns -ENODEV, which dosn't match the return value
of a non-existing block device with CONFIG_BLOCK, which is -ENXIO.
Just remove the extra implementation and fall back to the default
no_open_fops that always returns -ENXIO.

Fixes: 9361401e ("[PATCH] BLOCK: Make it possible to disable the block layer [try #6]")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20230508144405.41792-1-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

If anything goes wrong with the counters that track the number of
requests, I/O locks up. Make such scenarios easier to debug by adding
invariant checks for the request counters. Additionally, check that
BFQ queues are empty before these are freed.

Cc: Jan Kara <jack@suse.cz>
Cc: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20230516223853.1385255-1-bvanassche@acm.orgSigned-off-by: Jens Axboe <axboe@kernel.dk>

Before dispatching a zoned write from the FIFO list, check whether there
are any zoned writes in the RB-tree with a lower LBA for the same zone.
This patch ensures that zoned writes happen in order even if at_head is
set for some writes for a zone and not for others.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Cc: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20230517174230.897144-12-bvanassche@acm.orgSigned-off-by: Jens Axboe <axboe@kernel.dk>

Start dispatching from the start of a zone instead of from the starting
position of the most recently dispatched request.

If a zoned write is requeued with an LBA that is lower than already
inserted zoned writes, make sure that it is submitted first.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Cc: Damien Le Moal <dlemoal@kernel.org>
Cc: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Link: https://lore.kernel.org/r/20230517174230.897144-11-bvanassche@acm.orgSigned-off-by: Jens Axboe <axboe@kernel.dk>

Track the position (sector_t) of the most recently dispatched request
instead of tracking a pointer to the next request to dispatch. This
patch is the basis for patch "Handle requeued requests correctly".
Without this patch it would be significantly more complicated to make
sure that zoned writes are dispatched in LBA order per zone.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Cc: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20230517174230.897144-10-bvanassche@acm.orgSigned-off-by: Jens Axboe <axboe@kernel.dk>

blk_mq_free_requests() calls dd_finish_request() indirectly. Prevent
nested locking of dd->lock and dd->zone_lock by moving the code for
freeing requests.
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Cc: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20230517174230.897144-9-bvanassche@acm.orgSigned-off-by: Jens Axboe <axboe@kernel.dk>

Make the deadline_skip_seq_writes() code shorter without changing its
functionality.
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Cc: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20230517174230.897144-8-bvanassche@acm.orgSigned-off-by: Jens Axboe <axboe@kernel.dk>

Change the return type of deadline_check_fifo() from 'int' into 'bool'.
Use time_is_before_eq_jiffies() instead of time_after_eq(). No
functionality has been changed.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Cc: Damien Le Moal <dlemoal@kernel.org>
Cc: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Link: https://lore.kernel.org/r/20230517174230.897144-7-bvanassche@acm.orgSigned-off-by: Jens Axboe <axboe@kernel.dk>

Introduce the function blk_rq_is_seq_zoned_write(). This function will
be used in later patches to preserve the order of zoned writes that
require write serialization.

This patch includes an optimization: instead of using
rq->q->disk->part0->bd_queue to check whether or not the queue is
associated with a zoned block device, use rq->q->disk->queue.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Damien Le Moal <dlemoal@kernel.org>
Cc: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Link: https://lore.kernel.org/r/20230517174230.897144-6-bvanassche@acm.orgSigned-off-by: Jens Axboe <axboe@kernel.dk>

Introduce a helper function for checking whether write serialization is
required if the operation will be sent to a zoned device. A second caller
for op_needs_zoned_write_locking() will be introduced in the next patch
in this series.
Suggested-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Damien Le Moal <dlemoal@kernel.org>
Cc: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Link: https://lore.kernel.org/r/20230517174230.897144-5-bvanassche@acm.orgSigned-off-by: Jens Axboe <axboe@kernel.dk>

Change the type of the second argument of bdev_op_is_zoned_write() from
blk_opf_t into enum req_op because this function expects an operation
without flags as second argument.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Pankaj Raghav <p.raghav@samsung.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Cc: Ming Lei <ming.lei@redhat.com>
Fixes: 8cafdb5a ("block: adapt blk_mq_plug() to not plug for writes that require a zone lock")
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20230517174230.897144-4-bvanassche@acm.orgSigned-off-by: Jens Axboe <axboe@kernel.dk>

Remove the blk_rq_is_passthrough() check because it is redundant:
blk_req_needs_zone_write_lock() also calls bdev_op_is_zoned_write()
and the latter function returns false for pass-through requests.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20230517174230.897144-3-bvanassche@acm.orgSigned-off-by: Jens Axboe <axboe@kernel.dk>

Add the missing word "and".

Cc: Damien Le Moal <dlemoal@kernel.org>
Suggested-by: Damien Le Moal <dlemoal@kernel.org>
Fixes: 945ffb60 ("mq-deadline: add blk-mq adaptation of the deadline IO scheduler")
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Tested-by: Damien Le Moal <dlemoal@kernel.org>
Link: https://lore.kernel.org/r/20230517174230.897144-2-bvanassche@acm.orgSigned-off-by: Jens Axboe <axboe@kernel.dk>

In case of q->elevator, passthrough request can still be marked as
RQF_ELV, so some elevator callbacks will be called for them.

Fix this by splitting RQF_SCHED_TAGS, which is set for all requests that
are issued on a queue that uses an I/O scheduler, and RQF_USE_SCHED for
non-flush, non-passthrough requests on such a queue.

Roughly based on two different patches from
Ming Lei <ming.lei@redhat.com>.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20230518053101.760632-4-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

RQF_ELVPRIV is set for all non-flush requests that have RQF_ELV set.
Expand this condition in the two users of the flag and remove it.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20230518053101.760632-3-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

Passthrough requests should never be queued to the I/O scheduler,
as scheduling these opaque requests doesn't make sense, and I/O
schedulers might require req->bio to be always valid.

We never let passthrough requests insert into the scheduler before
commit 1c2d2fff ("block: wire-up support for passthrough plugging"),
restore this behavior even for passthrough requests issued under a plug.

[hch: use blk_mq_insert_requests for passthrough requests,
      fix up the commit message and comments]
Reported-by: Guangwu Zhang <guazhang@redhat.com>
Closes: https://lore.kernel.org/linux-block/CAGS2=YosaYaUTEMU3uaf+y=8MqSrhL7sYsJn8EwbaM=76p_4Qg@mail.gmail.com/Investigated-by: Yu Kuai <yukuai1@huaweicloud.com>
Fixes: 1c2d2fff ("block: wire-up support for passthrough plugging")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20230518053101.760632-2-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

See also:
* Commit 4d337ceb ("blk-mq: avoid to touch q->elevator without any protection").
* Commit 414dd48e ("blk-mq: add tagset quiesce interface").

Cc: Christoph Hellwig <hch@lst.de>
Cc: Damien Le Moal <dlemoal@kernel.org>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Chaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Link: https://lore.kernel.org/r/20230518222708.1190867-1-bvanassche@acm.orgSigned-off-by: Jens Axboe <axboe@kernel.dk>

XArray was introduced to hold large array of pointers with a simple API.
XArray API also provides array semantics which simplifies the way we store
and access the backing pages, and the code becomes significantly easier
to understand.

No performance difference was noticed between the two implementation
using fio with direct=1 [1].

[1] Performance in KIOPS:

          |  radix-tree |    XArray  |   Diff
          |             |            |
write     |    315      |     313    |   -0.6%
randwrite |    286      |     290    |   +1.3%
read      |    330      |     335    |   +1.5%
randread  |    309      |     312    |   +0.9%
Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Link: https://lore.kernel.org/r/20230511121544.111648-1-p.raghav@samsung.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

Pull compute express link fixes from Dan Williams:

 - Fix a compilation issue with DEFINE_STATIC_SRCU() in the unit tests

 - Fix leaking kernel memory to a root-only sysfs attribute

* tag 'cxl-fixes-6.4-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/cxl/cxl:
  cxl: Add missing return to cdat read error path
  tools/testing/cxl: Use DEFINE_STATIC_SRCU()

Pull parisc architecture fixes from Helge Deller:

 - Fix encoding of swp_entry due to added SWP_EXCLUSIVE flag

 - Include reboot.h to avoid gcc-12 compiler warning

* tag 'parisc-for-6.4-2' of git://git.kernel.org/pub/scm/linux/kernel/git/deller/parisc-linux:
  parisc: Fix encoding of swp_entry due to added SWP_EXCLUSIVE flag
  parisc: kexec: include reboot.h

Pull ARM fixes from Russell King:

 - fix unwinder for uleb128 case

 - fix kernel-doc warnings for HP Jornada 7xx

 - fix unbalanced stack on vfp success path

* tag 'for-linus' of git://git.armlinux.org.uk/~rmk/linux-arm:
  ARM: 9297/1: vfp: avoid unbalanced stack on 'success' return path
  ARM: 9296/1: HP Jornada 7XX: fix kernel-doc warnings
  ARM: 9295/1: unwind:fix unwind abort for uleb128 case

Pull locking fix from Borislav Petkov:

 - Make sure __down_read_common() is always inlined so that the callers'
   names land in traceevents output and thus the blocked function can be
   identified

* tag 'locking_urgent_for_v6.4_rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  locking/rwsem: Add __always_inline annotation to __down_read_common() and inlined callers

Pull perf fixes from Borislav Petkov:

 - Make sure the PEBS buffer is flushed before reprogramming the
   hardware so that the correct record sizes are used

 - Update the sample size for AMD BRS events

 - Fix a confusion with using the same on-stack struct with different
   events in the event processing path

* tag 'perf_urgent_for_v6.4_rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  perf/x86/intel/ds: Flush PEBS DS when changing PEBS_DATA_CFG
  perf/x86: Fix missing sample size update on AMD BRS
  perf/core: Fix perf_sample_data not properly initialized for different swevents in perf_tp_event()

Pull scheduler fix from Borislav Petkov:

 - Fix a couple of kernel-doc warnings

* tag 'sched_urgent_for_v6.4_rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched: fix cid_lock kernel-doc warnings

Pull x86 fix from Borislav Petkov:

 - Add the required PCI IDs so that the generic SMN accesses provided by
   amd_nb.c work for drivers which switch to them. Add a PCI device ID
   to k10temp's table so that latter is loaded on such systems too

* tag 'x86_urgent_for_v6.4_rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  hwmon: (k10temp) Add PCI ID for family 19, model 78h
  x86/amd_nb: Add PCI ID for family 19h model 78h