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selftests/ublk: add UBLK_F_SHMEM_ZC support for loop target

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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 <ming.lei@redhat.com>
Link: https://patch.msgid.link/20260331153207.3635125-7-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Ming Lei 2026-03-31 23:31:57 +08:00 committed by Jens Axboe
parent 166b476b8d
commit ec20aa44ac
1 changed files with 38 additions and 0 deletions
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38
tools/testing/selftests/ublk/file_backed.c
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@ -27,6 +27,40 @@ static int loop_queue_flush_io(struct ublk_thread *t, struct ublk_queue *q,
return 1;
}
/*
* Shared memory zero-copy I/O: when UBLK_IO_F_SHMEM_ZC is set, the
* request's data lives in a registered shared memory buffer. Decode
* index + offset from iod->addr and use the server's mmap of that
* buffer as the I/O buffer for the backing file.
*/
static int loop_queue_shmem_zc_io(struct ublk_thread *t, struct ublk_queue *q,
const struct ublksrv_io_desc *iod, int tag)
{
unsigned ublk_op = ublksrv_get_op(iod);
enum io_uring_op op = ublk_to_uring_op(iod, 0);
__u64 file_offset = iod->start_sector << 9;
__u32 len = iod->nr_sectors << 9;
__u32 shmem_idx = ublk_shmem_zc_index(iod->addr);
__u32 shmem_off = ublk_shmem_zc_offset(iod->addr);
struct io_uring_sqe *sqe[1];
void *addr;
if (shmem_idx >= UBLK_BUF_MAX || !shmem_table[shmem_idx].mmap_base)
return -EINVAL;
addr = shmem_table[shmem_idx].mmap_base + shmem_off;
ublk_io_alloc_sqes(t, sqe, 1);
if (!sqe[0])
return -ENOMEM;
io_uring_prep_rw(op, sqe[0], ublk_get_registered_fd(q, 1),
addr, len, file_offset);
io_uring_sqe_set_flags(sqe[0], IOSQE_FIXED_FILE);
sqe[0]->user_data = build_user_data(tag, ublk_op, 0, q->q_id, 1);
return 1;
}
static int loop_queue_tgt_rw_io(struct ublk_thread *t, struct ublk_queue *q,
const struct ublksrv_io_desc *iod, int tag)
{
@ -41,6 +75,10 @@ static int loop_queue_tgt_rw_io(struct ublk_thread *t, struct ublk_queue *q,
void *addr = io->buf_addr;
unsigned short buf_index = ublk_io_buf_idx(t, q, tag);
/* shared memory zero-copy path */
if (iod->op_flags & UBLK_IO_F_SHMEM_ZC)
return loop_queue_shmem_zc_io(t, q, iod, tag);
if (iod->op_flags & UBLK_IO_F_INTEGRITY) {
ublk_io_alloc_sqes(t, sqe, 1);
/* Use second backing file for integrity data */