linux.git/tools/testing/selftests/ublk, branch master

selftests: ublk: cap nthreads to kernel's actual nr_hw_queues

2026-05-13T13:55:39+00:00

dev->nthreads is derived from the user-requested queue count before the
ADD command, but the kernel may reduce nr_hw_queues (capped to
nr_cpu_ids). When the VM has fewer CPUs than requested queues, the
daemon creates more handler threads than there are kernel queues.

In non-batch mode, the extra threads access uninitialized queues
(q_depth=0), submit zero io_uring SQEs, and block forever in
io_cqring_wait. In batch mode, the extra threads cause similar hangs
during device removal.

In both cases, the stuck threads prevent the daemon from closing the
char device, holding the last ublk_device reference and causing
ublk_ctrl_del_dev() to hang in wait_event_interruptible().

Fix by capping dev->nthreads to the kernel-returned nr_hw_queues after
the ADD command completes. per_io_tasks mode is excluded because threads
interleave across all queues, so nthreads > nr_hw_queues is valid.

Fixes: abe54c160346 ("selftests: ublk: kublk: decouple ublk_queues from ublk server threads")
Signed-off-by: Ming Lei 
Link: https://patch.msgid.link/20260513101941.1373998-1-tom.leiming@gmail.com
Signed-off-by: Jens Axboe

selftests: ublk: add ublk auto integrity test

2026-04-23T10:52:43+00:00

The end-to-end integrity ublk selftest test_integrity_02 requires a
relatively recent fio version to support I/O with integrity buffers. Add
a version test_integrity_03 that uses the block layer's auto integrity
path instead. The auto integrity code doesn't check the application tag,
and doesn't indicate the bad guard/ref tag (just returns EILSEQ). But
it's a good smoke-test of the ublk integrity code and provides coverage
of the auto integrity path as well.

Signed-off-by: Caleb Sander Mateos 
Reviewed-by: Ming Lei 
Link: https://patch.msgid.link/20260421200901.1528842-4-csander@purestorage.com
Signed-off-by: Jens Axboe

selftests: ublk: enable test_integrity_02.sh on fio 3.42

2026-04-23T10:52:43+00:00

fio 3.42 was released with the needed fix for test_integrity_02.sh.
Allow 3.42 and newer in the fio version check.

Signed-off-by: Caleb Sander Mateos 
Reviewed-by: Ming Lei 
Link: https://patch.msgid.link/20260421200901.1528842-3-csander@purestorage.com
Signed-off-by: Jens Axboe

selftests: ublk: remove unused argument to _cleanup

2026-04-23T10:52:43+00:00

The _cleanup helper function doesn't take any arguments, so drop them
from its callers.

Signed-off-by: Caleb Sander Mateos 
Reviewed-by: Ming Lei 
Link: https://patch.msgid.link/20260421200901.1528842-2-csander@purestorage.com
Signed-off-by: Jens Axboe

selftests/ublk: add read-only buffer registration test

2026-04-07T13:42:39+00:00

Add --rdonly_shmem_buf option to kublk that registers shared memory
buffers with UBLK_SHMEM_BUF_READ_ONLY (read-only pinning without
FOLL_WRITE) and mmaps with PROT_READ only.

Add test_shmemzc_04.sh which exercises the new flag with a null target,
hugetlbfs buffer, and write workload. Write I/O works because the
server only reads from the shared buffer — the data flows from client
to kernel to the shared pages, and the server reads them out.

Signed-off-by: Ming Lei 
Link: https://patch.msgid.link/20260331153207.3635125-11-ming.lei@redhat.com
Signed-off-by: Jens Axboe

selftests/ublk: add filesystem fio verify test for shmem_zc

2026-04-07T13:42:23+00:00

Add test_shmemzc_03.sh which exercises shmem_zc through the full
filesystem stack: mkfs ext4 on the ublk device, mount it, then run
fio verify on a file inside the filesystem with --mem=mmaphuge.

Extend _mkfs_mount_test() to accept an optional command that runs
between mount and umount. The function cd's into the mount directory
so the command can use relative file paths. Existing callers that
pass only the device are unaffected.

Signed-off-by: Ming Lei 
Link: https://patch.msgid.link/20260331153207.3635125-10-ming.lei@redhat.com
Signed-off-by: Jens Axboe

selftests/ublk: add hugetlbfs shmem_zc test for loop target

2026-04-07T13:42:23+00:00

Add test_shmem_zc_02.sh which tests the UBLK_IO_F_SHMEM_ZC zero-copy
path on the loop target using a hugetlbfs shared buffer. Both kublk and
fio mmap the same hugetlbfs file with MAP_SHARED, sharing physical
pages. The kernel's PFN matching enables zero-copy — the loop target
reads/writes directly from the shared buffer to the backing file.

Uses standard fio --mem=mmaphuge: (supported since fio 1.10),
no patched fio required.

Signed-off-by: Ming Lei 
Link: https://patch.msgid.link/20260331153207.3635125-9-ming.lei@redhat.com
Signed-off-by: Jens Axboe

selftests/ublk: add shared memory zero-copy test

2026-04-07T13:42:23+00:00

Add test_shmem_zc_01.sh which tests UBLK_IO_F_SHMEM_ZC on the null
target using a hugetlbfs shared buffer. Both kublk (--htlb) and fio
(--mem=mmaphuge:) mmap the same hugetlbfs file with MAP_SHARED,
sharing physical pages. The kernel PFN match enables zero-copy I/O.

Uses standard fio --mem=mmaphuge: (supported since fio 1.10),
no patched fio required.

Signed-off-by: Ming Lei 
Link: https://patch.msgid.link/20260331153207.3635125-8-ming.lei@redhat.com
Signed-off-by: Jens Axboe

selftests/ublk: add UBLK_F_SHMEM_ZC support for loop target

2026-04-07T13:42:23+00:00

Add loop_queue_shmem_zc_io() which handles I/O requests marked with
UBLK_IO_F_SHMEM_ZC. When the kernel sets this flag, the request data
lives in a registered shared memory buffer — decode index + offset
from iod->addr and use the server's mmap as the I/O buffer.

The dispatch check in loop_queue_tgt_rw_io() routes SHMEM_ZC requests
to this new function, bypassing the normal buffer registration path.

Signed-off-by: Ming Lei 
Link: https://patch.msgid.link/20260331153207.3635125-7-ming.lei@redhat.com
Signed-off-by: Jens Axboe

selftests/ublk: add shared memory zero-copy support in kublk

2026-04-07T13:41:55+00:00

Add infrastructure for UBLK_F_SHMEM_ZC shared memory zero-copy:

- kublk.h: struct ublk_shmem_entry and table for tracking registered
  shared memory buffers
- kublk.c: per-device unix socket listener that accepts memfd
  registrations from clients via SCM_RIGHTS fd passing. The listener
  mmaps the memfd and registers the VA range with the kernel for PFN
  matching. Also adds --shmem_zc command line option.
- kublk.c: --htlb  option to open a pre-allocated hugetlbfs
  file, mmap it with MAP_SHARED|MAP_POPULATE, and register it with
  the kernel via ublk_ctrl_reg_buf(). Any process that mmaps the same
  hugetlbfs file shares the same physical pages, enabling zero-copy
  without socket-based fd passing.

Signed-off-by: Ming Lei 
Link: https://patch.msgid.link/20260331153207.3635125-6-ming.lei@redhat.com
Signed-off-by: Jens Axboe