[PATCH V2 3/5] ublk: use flexible array for ublk_queue.ios

[Ming Lei <ming.lei@redhat.com>]

Convert ublk_queue to use DECLARE_FLEX_ARRAY for the ios field and
use struct_size() for allocation, following kernel best practices.

Changes in this commit:

1. Convert ios field from "struct ublk_io ios[]" to use
   DECLARE_FLEX_ARRAY(struct ublk_io, ios) for consistency with
   modern kernel style.

2. Update ublk_init_queue() to use struct_size(ubq, ios, depth)
   instead of manual size calculation (sizeof(struct ublk_queue) +
   depth * sizeof(struct ublk_io)).

This provides better type safety and makes the code more maintainable
by using standard kernel macros for flexible array handling.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 drivers/block/ublk_drv.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index 394e9b5f512f..cef9cfa94feb 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -203,7 +203,8 @@ struct ublk_queue {
 	bool fail_io; /* copy of dev->state == UBLK_S_DEV_FAIL_IO */
 	spinlock_t		cancel_lock;
 	struct ublk_device *dev;
-	struct ublk_io ios[];
+
+	DECLARE_FLEX_ARRAY(struct ublk_io, ios);
 };
 
 struct ublk_device {
@@ -2700,7 +2701,6 @@ static int ublk_get_queue_numa_node(struct ublk_device *ub, int q_id)
 static int ublk_init_queue(struct ublk_device *ub, int q_id)
 {
 	int depth = ub->dev_info.queue_depth;
-	int ubq_size = sizeof(struct ublk_queue) + depth * sizeof(struct ublk_io);
 	gfp_t gfp_flags = GFP_KERNEL | __GFP_ZERO;
 	struct ublk_queue *ubq;
 	struct page *page;
@@ -2711,7 +2711,8 @@ static int ublk_init_queue(struct ublk_device *ub, int q_id)
 	numa_node = ublk_get_queue_numa_node(ub, q_id);
 
 	/* Allocate queue structure on local NUMA node */
-	ubq = kvzalloc_node(ubq_size, GFP_KERNEL, numa_node);
+	ubq = kvzalloc_node(struct_size(ubq, ios, depth), GFP_KERNEL,
+			    numa_node);
 	if (!ubq)
 		return -ENOMEM;
 
-- 
2.47.0