On Fri, Jun 20, 2025 at 09:10:03AM -0600, Caleb Sander Mateos wrote:

Currently, UBLK_IO_REGISTER_IO_BUF and UBLK_IO_UNREGISTER_IO_BUF are
only permitted on the ublk_io's daemon task. But this restriction is
unnecessary. ublk_register_io_buf() calls __ublk_check_and_get_req() to
look up the request from the tagset and atomically take a reference on
the request without accessing the ublk_io. ublk_unregister_io_buf()
doesn't use the q_id or tag at all.

So allow these opcodes even on tasks other than io->task.

Handle UBLK_IO_UNREGISTER_IO_BUF before obtaining the ubq and io since
the buffer index being unregistered is not necessarily related to the
specified q_id and tag.

Add a feature flag UBLK_F_BUF_REG_OFF_DAEMON that userspace can use to
determine whether the kernel supports off-daemon buffer registration.

Suggested-by: Ming Lei <redacted>
Signed-off-by: Caleb Sander Mateos <redacted>

Reviewed-by: Ming Lei <redacted>

Thanks,
Ming