[PATCH v6.15 2/3] ublk: decouple zero copy from user copy

Ming Lei
2025-04-27T13:49:58Z

UBLK_F_USER_COPY and UBLK_F_SUPPORT_ZERO_COPY are two different
features, and shouldn't be coupled together.

Commit 1f6540e2aabb ("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: 1f6540e2aabb ("ublk: zc register/unregister bvec")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
drivers/block/ublk_drv.c | 35 +++++++++++++++++++++++------------
1 file changed, 23 insertions(+), 12 deletions(-)

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index 40f971a66d3e..0a3a3c64316d 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -205,11 +205,6 @@ static inline struct request *__ublk_check_and_get_req(struct ublk_device *ub,
static inline unsigned int ublk_req_build_flags(struct request *req);
static inline struct ublksrv_io_desc *ublk_get_iod(struct ublk_queue *ubq,
int tag);
-static inline bool ublk_dev_is_user_copy(const struct ublk_device *ub)
-{
- return ub->dev_info.flags & (UBLK_F_USER_COPY | UBLK_F_SUPPORT_ZERO_COPY);
-}
-
static inline bool ublk_dev_is_zoned(const struct ublk_device *ub)
{
return ub->dev_info.flags & UBLK_F_ZONED;
@@ -609,14 +604,19 @@ static void ublk_apply_params(struct ublk_device *ub)
ublk_dev_param_zoned_apply(ub);
}

+static inline bool ublk_support_zero_copy(const struct ublk_queue *ubq)
+{
+ return ubq->flags & UBLK_F_SUPPORT_ZERO_COPY;
+}
+
static inline bool ublk_support_user_copy(const struct ublk_queue *ubq)
{
- return ubq->flags & (UBLK_F_USER_COPY | UBLK_F_SUPPORT_ZERO_COPY);
+ return ubq->flags & UBLK_F_USER_COPY;
}

static inline bool ublk_need_map_io(const struct ublk_queue *ubq)
{
- return !ublk_support_user_copy(ubq);
+ return !ublk_support_user_copy(ubq) && !ublk_support_zero_copy(ubq);
}

static inline bool ublk_need_req_ref(const struct ublk_queue *ubq)
@@ -624,8 +624,11 @@ static inline bool ublk_need_req_ref(const struct ublk_queue *ubq)
/*
* read()/write() is involved in user copy, so request reference
* has to be grabbed
+ *
+ * for zero copy, request buffer need to be registered to io_uring
+ * buffer table, so reference is needed
*/
- return ublk_support_user_copy(ubq);
+ return ublk_support_user_copy(ubq) || ublk_support_zero_copy(ubq);
}

static inline void ublk_init_req_ref(const struct ublk_queue *ubq,
@@ -2245,6 +2248,9 @@ static struct request *ublk_check_and_get_req(struct kiocb *iocb,
if (!ubq)
return ERR_PTR(-EINVAL);

+ if (!ublk_support_user_copy(ubq))
+ return ERR_PTR(-EACCES);
+
if (tag >= ubq->q_depth)
return ERR_PTR(-EINVAL);

@@ -2783,13 +2789,18 @@ static int ublk_ctrl_add_dev(const struct ublksrv_ctrl_cmd *header)
ub->dev_info.flags |= UBLK_F_CMD_IOCTL_ENCODE |
UBLK_F_URING_CMD_COMP_IN_TASK;

- /* GET_DATA isn't needed any more with USER_COPY */
- if (ublk_dev_is_user_copy(ub))
+ /* GET_DATA isn't needed any more with USER_COPY or ZERO COPY */
+ if (ub->dev_info.flags & (UBLK_F_USER_COPY | UBLK_F_SUPPORT_ZERO_COPY))
ub->dev_info.flags &= ~UBLK_F_NEED_GET_DATA;

- /* Zoned storage support requires user copy feature */
+ /*
+ * Zoned storage support requires reuse `ublksrv_io_cmd->addr` for
+ * returning write_append_lba, which is only allowed in case of
+ * user copy or zero copy
+ */
if (ublk_dev_is_zoned(ub) &&
- (!IS_ENABLED(CONFIG_BLK_DEV_ZONED) || !ublk_dev_is_user_copy(ub))) {
+ (!IS_ENABLED(CONFIG_BLK_DEV_ZONED) || !(ub->dev_info.flags &
+ (UBLK_F_USER_COPY | UBLK_F_SUPPORT_ZERO_COPY)))) {
ret = -EINVAL;
goto out_free_dev_number;
}
--
2.47.0