In case of a ZONE APPEND write, regardless of native ZONE APPEND or the
emulation layer in the zone write plugging code, the sector the data got
written to by the device needs to be updated in the bio.
At the moment, this is done for every native ZONE APPEND write and every
request that is flagged with 'BIO_ZONE_WRITE_PLUGGING'. But thus
superfluously updates the sector for regular writes to a zoned block
device.
Check if a bio is a native ZONE APPEND write or if the bio is flagged as
'BIO_EMULATES_ZONE_APPEND', meaning the block layer's zone write plugging
code handles the ZONE APPEND and translates it into a regular write and
back. Only if one of these two criterion is met, update the sector in the
bio upon completion.
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/dea089581cb6b777c1cd1500b38ac0b61df4b2d1.1746530748.git.jth@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
After calling nvme_auth_derive_tls_psk() we need to free the resulting
psk data, as either TLS is disable (and we don't need the data anyway)
or the psk data is copied into the resulting key (and can be free, too).
Fixes: fa2e0f8bbc ("nvmet-tcp: support secure channel concatenation")
Reported-by: Yi Zhang <yi.zhang@redhat.com>
Suggested-by: Maurizio Lombardi <mlombard@bsdbackstore.eu>
Signed-off-by: Hannes Reinecke <hare@kernel.org>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Tested-by: Yi Zhang <yi.zhang@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Ensure that TLS support is enabled in the kernel when
CONFIG_NVME_TARGET_TCP_TLS is enabled. Without this the code compiles,
but does not actually work unless something else enables CONFIG_TLS.
Fixes: 675b453e02 ("nvmet-tcp: enable TLS handshake upcall")
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Ensure that TLS support is enabled in the kernel when
CONFIG_NVME_TCP_TLS is enabled. Without this the code compiles, but does
not actually work unless something else enables CONFIG_TLS.
Fixes: be8e82caa6 ("nvme-tcp: enable TLS handshake upcall")
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
This patch addresses a data corruption issue observed in nvme-tcp during
testing.
In an NVMe native multipath setup, when an I/O timeout occurs, all
inflight I/Os are canceled almost immediately after the kernel socket is
shut down. These canceled I/Os are reported as host path errors,
triggering a failover that succeeds on a different path.
However, at this point, the original I/O may still be outstanding in the
host's network transmission path (e.g., the NIC’s TX queue). From the
user-space app's perspective, the buffer associated with the I/O is
considered completed since they're acked on the different path and may
be reused for new I/O requests.
Because nvme-tcp enables zero-copy by default in the transmission path,
this can lead to corrupted data being sent to the original target,
ultimately causing data corruption.
We can reproduce this data corruption by injecting delay on one path and
triggering i/o timeout.
To prevent this issue, this change ensures that all inflight
transmissions are fully completed from host's perspective before
returning from queue stop. To handle concurrent I/O timeout from multiple
namespaces under the same controller, always wait in queue stop
regardless of queue's state.
This aligns with the behavior of queue stopping in other NVMe fabric
transports.
Fixes: 3f2304f8c6 ("nvme-tcp: add NVMe over TCP host driver")
Signed-off-by: Michael Liang <mliang@purestorage.com>
Reviewed-by: Mohamed Khalfella <mkhalfella@purestorage.com>
Reviewed-by: Randy Jennings <randyj@purestorage.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Add two quirks for the WDC Blue SN550 (PCI ID 15b7:5009) based on user
reports and hardware analysis:
- NVME_QUIRK_NO_DEEPEST_PS:
liaozw talked to me the problem and solved with
nvme_core.default_ps_max_latency_us=0, so add the quirk.
I also found some reports in the following link.
- NVME_QUIRK_BROKEN_MSI:
after get the lspci from Jack Rio.
I think that the disk also have NVME_QUIRK_BROKEN_MSI.
described in commit d5887dc6b6 ("nvme-pci: Add quirk for broken MSIs")
as sean said in link which match the MSI 1/32 and MSI-X 17.
Log:
lspci -nn | grep -i memory
03:00.0 Non-Volatile memory controller [0108]: Sandisk Corp SanDisk Ultra 3D / WD PC SN530, IX SN530, Blue SN550 NVMe SSD (DRAM-less) [15b7:5009] (rev 01)
lspci -v -d 15b7:5009
03:00.0 Non-Volatile memory controller: Sandisk Corp SanDisk Ultra 3D / WD PC SN530, IX SN530, Blue SN550 NVMe SSD (DRAM-less) (rev 01) (prog-if 02 [NVM Express])
Subsystem: Sandisk Corp WD Blue SN550 NVMe SSD
Flags: bus master, fast devsel, latency 0, IRQ 35, IOMMU group 10
Memory at fe800000 (64-bit, non-prefetchable) [size=16K]
Memory at fe804000 (64-bit, non-prefetchable) [size=256]
Capabilities: [80] Power Management version 3
Capabilities: [90] MSI: Enable- Count=1/32 Maskable- 64bit+
Capabilities: [b0] MSI-X: Enable+ Count=17 Masked-
Capabilities: [c0] Express Endpoint, MSI 00
Capabilities: [100] Advanced Error Reporting
Capabilities: [150] Device Serial Number 00-00-00-00-00-00-00-00
Capabilities: [1b8] Latency Tolerance Reporting
Capabilities: [300] Secondary PCI Express
Capabilities: [900] L1 PM Substates
Kernel driver in use: nvme
dmesg | grep nvme
[ 0.000000] Command line: BOOT_IMAGE=/vmlinuz-6.12.20-amd64-desktop-rolling root=UUID= ro splash quiet nvme_core.default_ps_max_latency_us=0 DEEPIN_GFXMODE=
[ 0.059301] Kernel command line: BOOT_IMAGE=/vmlinuz-6.12.20-amd64-desktop-rolling root=UUID= ro splash quiet nvme_core.default_ps_max_latency_us=0 DEEPIN_GFXMODE=
[ 0.542430] nvme nvme0: pci function 0000:03:00.0
[ 0.560426] nvme nvme0: allocated 32 MiB host memory buffer.
[ 0.562491] nvme nvme0: 16/0/0 default/read/poll queues
[ 0.567764] nvme0n1: p1 p2 p3 p4 p5 p6 p7 p8 p9
[ 6.388726] EXT4-fs (nvme0n1p7): mounted filesystem ro with ordered data mode. Quota mode: none.
[ 6.893421] EXT4-fs (nvme0n1p7): re-mounted r/w. Quota mode: none.
[ 7.125419] Adding 16777212k swap on /dev/nvme0n1p8. Priority:-2 extents:1 across:16777212k SS
[ 7.157588] EXT4-fs (nvme0n1p6): mounted filesystem r/w with ordered data mode. Quota mode: none.
[ 7.165021] EXT4-fs (nvme0n1p9): mounted filesystem r/w with ordered data mode. Quota mode: none.
[ 8.036932] nvme nvme0: using unchecked data buffer
[ 8.096023] block nvme0n1: No UUID available providing old NGUID
Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d5887dc6b6c054d0da3cd053afc15b7be1f45ff6
Link: https://lore.kernel.org/all/20240422162822.3539156-1-sean.anderson@linux.dev/
Reported-by: liaozw <hedgehog-002@163.com>
Closes: https://bbs.deepin.org.cn/post/286300
Reported-by: rugk <rugk+github@posteo.de>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=208123
Signed-off-by: Wentao Guan <guanwentao@uniontech.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
A zero return means the reset was successfully scheduled. We don't want
to unquiesce the queues while the reset_work is pending, as that will
just flush out requeued requests to a failed completion.
Fixes: 71a5bb153b ("nvme: ensure disabling pairs with unquiesce")
Reported-by: Dhankaran Singh Ajravat <dhankaran@meta.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
The simple check of UBLK_IO_FLAG_OWNED_BY_SRV can avoid incorrect
register/unregister io buffer easily, so check it before calling
starting to register/un-register io buffer.
Also only allow io buffer register/unregister uring_cmd in case of
UBLK_F_SUPPORT_ZERO_COPY.
Also mark argument 'ublk_queue *' of ublk_register_io_buf as const.
Reviewed-by: Caleb Sander Mateos <csander@purestorage.com>
Fixes: 1f6540e2aa ("ublk: zc register/unregister bvec")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250429022941.1718671-4-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
UBLK_F_USER_COPY and UBLK_F_SUPPORT_ZERO_COPY are two different
features, and shouldn't be coupled together.
Commit 1f6540e2aa ("ublk: zc register/unregister bvec") enables
user copy automatically in case of UBLK_F_SUPPORT_ZERO_COPY, this way
isn't correct.
So decouple zero copy from user copy, and use independent helper to
check each one.
Fixes: 1f6540e2aa ("ublk: zc register/unregister bvec")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250429022941.1718671-3-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Commit 57e13a2e8c ("selftests: ublk: support user recovery") starts to
support UBLK_F_NEED_GET_DATA for covering recovery feature, however the
ublk utility implementation isn't done correctly.
Fix it by supporting UBLK_F_NEED_GET_DATA correctly.
Also add test generic_07 for covering UBLK_F_NEED_GET_DATA.
Reviewed-by: Caleb Sander Mateos <csander@purestorage.com>
Fixes: 57e13a2e8c ("selftests: ublk: support user recovery")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250429022941.1718671-2-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
We call io_uring_cmd_complete_in_task() to schedule task_work for handling
UBLK_U_IO_NEED_GET_DATA.
This way is really not necessary because the current context is exactly
the ublk queue context, so call ublk_dispatch_req() directly for handling
UBLK_U_IO_NEED_GET_DATA.
Fixes: 216c8f5ef0 ("ublk: replace monitor with cancelable uring_cmd")
Tested-by: Jared Holzman <jholzman@nvidia.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250425013742.1079549-2-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
When the user increased the read-ahead size through sysfs this value
currently get lost if the device is reprobe, including on a resume
from suspend.
As there is no hardware limitation for the read-ahead size there is
no real need to reset it or track a separate hardware limitation
like for max_sectors.
This restores the pre-atomic queue limit behavior in the sd driver as
sd did not use blk_queue_io_opt and thus never updated the read ahead
size to the value based of the optimal I/O, but changes behavior for
all other drivers. As the new behavior seems useful and sd is the
driver for which the readahead size tweaks are most useful that seems
like a worthwhile trade off.
Fixes: 804e498e04 ("sd: convert to the atomic queue limits API")
Reported-by: Holger Hoffstätte <holger@applied-asynchrony.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: Holger Hoffstätte <holger@applied-asynchrony.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Link: https://lore.kernel.org/r/20250424082521.1967286-1-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Pull NVMe fix from Christoph:
"nvme fixes for Linux 6.15
- fix an out-of-bounds access in nvmet_enable_port (Richard Weinberger)"
* tag 'nvme-6.15-2025-04-24' of git://git.infradead.org/nvme:
nvmet: fix out-of-bounds access in nvmet_enable_port
With the new large sector size support, it's now the case that
set_blocksize can change i_blksize and the folio order in a manner that
conflicts with a concurrent reader and causes a kernel crash.
Specifically, let's say that udev-worker calls libblkid to detect the
labels on a block device. The read call can create an order-0 folio to
read the first 4096 bytes from the disk. But then udev is preempted.
Next, someone tries to mount an 8k-sectorsize filesystem from the same
block device. The filesystem calls set_blksize, which sets i_blksize to
8192 and the minimum folio order to 1.
Now udev resumes, still holding the order-0 folio it allocated. It then
tries to schedule a read bio and do_mpage_readahead tries to create
bufferheads for the folio. Unfortunately, blocks_per_folio == 0 because
the page size is 4096 but the blocksize is 8192 so no bufferheads are
attached and the bh walk never sets bdev. We then submit the bio with a
NULL block device and crash.
Therefore, truncate the page cache after flushing but before updating
i_blksize. However, that's not enough -- we also need to lock out file
IO and page faults during the update. Take both the i_rwsem and the
invalidate_lock in exclusive mode for invalidations, and in shared mode
for read/write operations.
I don't know if this is the correct fix, but xfs/259 found it.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Tested-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Link: https://lore.kernel.org/r/174543795699.4139148.2086129139322431423.stgit@frogsfrogsfrogs
Signed-off-by: Jens Axboe <axboe@kernel.dk>
When trying to enable a port that has no transport configured yet,
nvmet_enable_port() uses NVMF_TRTYPE_MAX (255) to query the transports
array, causing an out-of-bounds access:
[ 106.058694] BUG: KASAN: global-out-of-bounds in nvmet_enable_port+0x42/0x1da
[ 106.058719] Read of size 8 at addr ffffffff89dafa58 by task ln/632
[...]
[ 106.076026] nvmet: transport type 255 not supported
Since commit 200adac758, NVMF_TRTYPE_MAX is the default state as configured by
nvmet_ports_make().
Avoid this by checking for NVMF_TRTYPE_MAX before proceeding.
Fixes: 200adac758 ("nvme: Add PCI transport type")
Signed-off-by: Richard Weinberger <richard@nod.at>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Pull NVMe fixes from Christoph:
"nvme fixes for Linux 6.15
- fix scan failure for non-ANA multipath controllers (Hannes Reinecke)
- fix multipath sysfs links creation for some cases (Hannes Reinecke)
- PCIe endpoint fixes (Damien Le Moal)
- use NULL instead of 0 in the auth code (Damien Le Moal)"
* tag 'nvme-6.15-2025-04-17' of git://git.infradead.org/nvme:
nvmet: pci-epf: cleanup link state management
nvmet: pci-epf: clear CC and CSTS when disabling the controller
nvmet: pci-epf: always fully initialize completion entries
nvmet: auth: use NULL to clear a pointer in nvmet_auth_sq_free()
nvme-multipath: sysfs links may not be created for devices
nvme: fixup scan failure for non-ANA multipath controllers
Now ublk_abort_queue() is moved to ublk char device release handler,
meantime our request queue is "quiesced" because either ->canceling was
set from uring_cmd cancel function or all IOs are inflight and can't be
completed by ublk server, things becomes easy much:
- all uring_cmd are done, so we needn't to mark io as UBLK_IO_FLAG_ABORTED
for handling completion from uring_cmd
- ublk char device is closed, no one can hold IO request reference any more,
so we can simply complete this request or requeue it for ublk_nosrv_should_reissue_outstanding.
Reviewed-by: Uday Shankar <ushankar@purestorage.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250416035444.99569-8-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Remove __ublk_quiesce_dev() and open code for updating device state as
QUIESCED.
We needn't to drain inflight requests in __ublk_quiesce_dev() any more,
because all inflight requests are aborted in ublk char device release
handler.
Also we needn't to set ->canceling in __ublk_quiesce_dev() any more
because it is done unconditionally now in ublk_ch_release().
Reviewed-by: Uday Shankar <ushankar@purestorage.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250416035444.99569-7-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
There are currently two ways in which ublk server exit is detected by
ublk_drv:
1. uring_cmd cancellation. If there are any outstanding uring_cmds which
have not been completed to the ublk server when it exits, io_uring
calls the uring_cmd callback with a special cancellation flag as the
issuing task is exiting.
2. I/O timeout. This is needed in addition to the above to handle the
"saturated queue" case, when all I/Os for a given queue are in the
ublk server, and therefore there are no outstanding uring_cmds to
cancel when the ublk server exits.
There are a couple of issues with this approach:
- It is complex and inelegant to have two methods to detect the same
condition
- The second method detects ublk server exit only after a long delay
(~30s, the default timeout assigned by the block layer). This delays
the nosrv behavior from kicking in and potential subsequent recovery
of the device.
The second issue is brought to light with the new test_generic_06 which
will be added in following patch. It fails before this fix:
selftests: ublk: test_generic_06.sh
dev id is 0
dd: error writing '/dev/ublkb0': Input/output error
1+0 records in
0+0 records out
0 bytes copied, 30.0611 s, 0.0 kB/s
DEAD
dd took 31 seconds to exit (>= 5s tolerance)!
generic_06 : [FAIL]
Fix this by instead detecting and handling ublk server exit in the
character file release callback. This has several advantages:
- This one place can handle both saturated and unsaturated queues. Thus,
it replaces both preexisting methods of detecting ublk server exit.
- It runs quickly on ublk server exit - there is no 30s delay.
- It starts the process of removing task references in ublk_drv. This is
needed if we want to relax restrictions in the driver like letting
only one thread serve each queue
There is also the disadvantage that the character file release callback
can also be triggered by intentional close of the file, which is a
significant behavior change. Preexisting ublk servers (libublksrv) are
dependent on the ability to open/close the file multiple times. To
address this, only transition to a nosrv state if the file is released
while the ublk device is live. This allows for programs to open/close
the file multiple times during setup. It is still a behavior change if a
ublk server decides to close/reopen the file while the device is LIVE
(i.e. while it is responsible for serving I/O), but that would be highly
unusual. This behavior is in line with what is done by FUSE, which is
very similar to ublk in that a userspace daemon is providing services
traditionally provided by the kernel.
With this change in, the new test (and all other selftests, and all
ublksrv tests) pass:
selftests: ublk: test_generic_06.sh
dev id is 0
dd: error writing '/dev/ublkb0': Input/output error
1+0 records in
0+0 records out
0 bytes copied, 0.0376731 s, 0.0 kB/s
DEAD
generic_04 : [PASS]
Signed-off-by: Uday Shankar <ushankar@purestorage.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250416035444.99569-6-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
ublk_ch_release() is called after ublk char device is closed, when all
uring_cmd are done, so it is perfect fine to move ublk device reset to
ublk_ch_release() from ublk_ctrl_start_recovery().
This way can avoid to grab the exiting daemon task_struct too long.
However, reset of the following ublk IO flags has to be moved until ublk
io_uring queues are ready:
- ubq->canceling
For requeuing IO in case of ublk_nosrv_dev_should_queue_io() before device
is recovered
- ubq->fail_io
For failing IO in case of UBLK_F_USER_RECOVERY_FAIL_IO before device is
recovered
- ublk_io->flags
For preventing using io->cmd
With this way, recovery is simplified a lot.
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250416035444.99569-5-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Now ublk deals with ublk_nosrv_dev_should_queue_io() by keeping request
queue as quiesced. This way is fragile because queue quiesce crosses syscalls
or process contexts.
Switch to rely on ubq->canceling for dealing with
ublk_nosrv_dev_should_queue_io(), because it has been used for this purpose
during io_uring context exiting, and it can be reused before recovering too.
In ublk_queue_rq(), the request will be added to requeue list without
kicking off requeue in case of ubq->canceling, and finally requests added in
requeue list will be dispatched from either ublk_stop_dev() or
ublk_ctrl_end_recovery().
Meantime we have to move reset of ubq->canceling from ublk_ctrl_start_recovery()
to ublk_ctrl_end_recovery(), when IO handling can be recovered completely.
Then blk_mq_quiesce_queue() and blk_mq_unquiesce_queue() are always used
in same context.
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Uday Shankar <ushankar@purestorage.com>
Link: https://lore.kernel.org/r/20250416035444.99569-4-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Most uring_cmds issued against ublk character devices are serialized
because each command affects only one queue, and there is an early check
which only allows a single task (the queue's ubq_daemon) to issue
uring_cmds against that queue. However, this mechanism does not work for
FETCH_REQs, since they are expected before ubq_daemon is set. Since
FETCH_REQs are only used at initialization and not in the fast path,
serialize them using the per-ublk-device mutex. This fixes a number of
data races that were previously possible if a badly behaved ublk server
decided to issue multiple FETCH_REQs against the same qid/tag
concurrently.
Reported-by: Caleb Sander Mateos <csander@purestorage.com>
Signed-off-by: Uday Shankar <ushankar@purestorage.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250416035444.99569-2-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
test may exit early because of missing program or not having required
feature before calling _prep_test(), then $UBLK_TMP isn't cleaned.
Fix it by moving creating $UBLK_TMP into _prep_test(), any resources
created since _prep_test() will be cleaned by _cleanup_test().
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250412023035.2649275-14-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
In NUMA machine, ublk IO performance is very sensitive with queue
pthread's affinity setting.
Retrieve queue's affinity and select the 1st cpu as queue thread's sched
affinity, and it is observed that single cpu task affinity can get
stable & good performance if client application is put on proper cpu.
Dump this info when adding one ublk device. Use shmem to communicate
queue's tid between parent and daemon.
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250412023035.2649275-9-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Detach ublk daemon from the starting process completely by double-fork and
clearing its process group, so that `_add_ublk_dev` can return from sub-shell.
Then it is more friendly for writing shell test script for adding/recovering
ublk device.
Prepare for running ublk test in parallel.
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250412023035.2649275-5-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
