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ublk: allow UBLK_IO_(UN)REGISTER_IO_BUF on any task

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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 <ming.lei@redhat.com>
Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250620151008.3976463-10-csander@purestorage.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Caleb Sander Mateos
2025-06-20 09:10:03 -06:00
committed by Jens Axboe
parent 2da1e7bb3f
commit 763ff02ce2
2 changed files with 32 additions and 5 deletions
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10
include/uapi/linux/ublk_cmd.h
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@@ -301,6 +301,16 @@
*/
#define UBLK_F_PER_IO_DAEMON (1ULL << 13)
/*
* If this feature is set, UBLK_U_IO_REGISTER_IO_BUF/UBLK_U_IO_UNREGISTER_IO_BUF
* can be issued for an I/O on any task. q_id and tag are also ignored in
* UBLK_U_IO_UNREGISTER_IO_BUF's ublksrv_io_cmd.
* If it is unset, zero-copy buffers can only be registered and unregistered by
* the I/O's daemon task. The q_id and tag of the registered buffer are required
* in UBLK_U_IO_UNREGISTER_IO_BUF's ublksrv_io_cmd.
*/
#define UBLK_F_BUF_REG_OFF_DAEMON (1ULL << 14)
/* device state */
#define UBLK_S_DEV_DEAD 0
#define UBLK_S_DEV_LIVE 1