Re: [PATCH v2 1/1] scsi: qla2xxx: replace non-standard flexible array purex_item.iocb

["Gustavo A. R. Silva" <gustavo@embeddedor.com>]

On 28/07/25 19:37, Gustavo A. R. Silva wrote:
> 
>> default item was replaced with the header and a static sized array,
>> cast to a purex_item * when returned through the alloc function
>>
>>    -       struct purex_item default_item;
>>    +       struct purex_item_hdr default_item;
>>    +       uint8_t __default_item_iocb[QLA_DEFAULT_PAYLOAD_SIZE];
> 
> I see; yeah, this works as `(struct purex_item *)default_item->iocb`
> and `__default_item_iocb` happen to be just perfectly aligned. However,
> I wonder if there is any chance of this changing in the future...
> 
> Probably, a code comment stating that both `(struct purex_item *)default_item->iocb`
> and `__default_item_iocb` are expected to share the same address would
> likely be helpful for anyone modifying something around this code in
> the future.
> 
> BTW, instead of directly casting to `struct purex_item *`, you could
> use `container_of()` like this:
> 
> item = container_of(&vha->default_item, struct purex_item, __hdr);
> 
> but I guess that's up to maintainer's preference.
> 

I just noticed that the new TRAILING_OVERLAP() helper just landed in
Linus' tree, and this issue seems to be a perfect candidate for it.

The (untested) patch below avoids the use of `struct_group_tagged()`
and the casts to `struct purex_item *`:

diff --git a/drivers/scsi/qla2xxx/qla_def.h b/drivers/scsi/qla2xxx/qla_def.h
index cb95b7b12051..4bdf8adf04ed 100644
--- a/drivers/scsi/qla2xxx/qla_def.h
+++ b/drivers/scsi/qla2xxx/qla_def.h
@@ -4890,9 +4890,7 @@ struct purex_item {
                              struct purex_item *pkt);
         atomic_t in_use;
         uint16_t size;
-       struct {
-               uint8_t iocb[64];
-       } iocb;
+       uint8_t iocb[] __counted_by(size);
  };

  #include "qla_edif.h"
@@ -5101,7 +5099,6 @@ typedef struct scsi_qla_host {
                 struct list_head head;
                 spinlock_t lock;
         } purex_list;
-       struct purex_item default_item;

         struct name_list_extended gnl;
         /* Count of active session/fcport */
@@ -5130,6 +5127,10 @@ typedef struct scsi_qla_host {
  #define DPORT_DIAG_IN_PROGRESS                 BIT_0
  #define DPORT_DIAG_CHIP_RESET_IN_PROGRESS      BIT_1
         uint16_t dport_status;
+
+       TRAILING_OVERLAP(struct purex_item, default_item, iocb,
+               uint8_t __default_item_iocb[QLA_DEFAULT_PAYLOAD_SIZE];
+       );
  } scsi_qla_host_t;

  struct qla27xx_image_status {
diff --git a/drivers/scsi/qla2xxx/qla_isr.c b/drivers/scsi/qla2xxx/qla_isr.c
index c4c6b5c6658c..4559b490614d 100644
--- a/drivers/scsi/qla2xxx/qla_isr.c
+++ b/drivers/scsi/qla2xxx/qla_isr.c
@@ -1077,17 +1077,17 @@ static struct purex_item *
  qla24xx_alloc_purex_item(scsi_qla_host_t *vha, uint16_t size)
  {
         struct purex_item *item = NULL;
-       uint8_t item_hdr_size = sizeof(*item);

         if (size > QLA_DEFAULT_PAYLOAD_SIZE) {
-               item = kzalloc(item_hdr_size +
-                   (size - QLA_DEFAULT_PAYLOAD_SIZE), GFP_ATOMIC);
+               item = kzalloc(struct_size(item, iocb, size), GFP_ATOMIC);
         } else {
                 if (atomic_inc_return(&vha->default_item.in_use) == 1) {
                         item = &vha->default_item;
                         goto initialize_purex_header;
                 } else {
-                       item = kzalloc(item_hdr_size, GFP_ATOMIC);
+                       item = kzalloc(
+                               struct_size(item, iocb, QLA_DEFAULT_PAYLOAD_SIZE),
+                               GFP_ATOMIC);
                 }
         }
         if (!item) {
@@ -1127,17 +1127,16 @@ qla24xx_queue_purex_item(scsi_qla_host_t *vha, struct purex_item *pkt,
   * @vha: SCSI driver HA context
   * @pkt: ELS packet
   */
-static struct purex_item
-*qla24xx_copy_std_pkt(struct scsi_qla_host *vha, void *pkt)
+static struct purex_item *
+qla24xx_copy_std_pkt(struct scsi_qla_host *vha, void *pkt)
  {
         struct purex_item *item;

-       item = qla24xx_alloc_purex_item(vha,
-                                       QLA_DEFAULT_PAYLOAD_SIZE);
+       item = qla24xx_alloc_purex_item(vha, QLA_DEFAULT_PAYLOAD_SIZE);
         if (!item)
                 return item;

-       memcpy(&item->iocb, pkt, sizeof(item->iocb));
+       memcpy(&item->iocb, pkt, QLA_DEFAULT_PAYLOAD_SIZE);
         return item;
  }

diff --git a/drivers/scsi/qla2xxx/qla_nvme.c b/drivers/scsi/qla2xxx/qla_nvme.c
index 8ee2e337c9e1..92488890bc04 100644
--- a/drivers/scsi/qla2xxx/qla_nvme.c
+++ b/drivers/scsi/qla2xxx/qla_nvme.c
@@ -1308,7 +1308,7 @@ void qla2xxx_process_purls_iocb(void **pkt, struct rsp_que **rsp)

         ql_dbg(ql_dbg_unsol, vha, 0x2121,
                "PURLS OP[%01x] size %d xchg addr 0x%x portid %06x\n",
-              item->iocb.iocb[3], item->size, uctx->exchange_address,
+              item->iocb[3], item->size, uctx->exchange_address,
                fcport->d_id.b24);
         /* +48    0  1  2  3  4  5  6  7  8  9  A  B  C  D  E  F
          * ----- -----------------------------------------------
diff --git a/drivers/scsi/qla2xxx/qla_os.c b/drivers/scsi/qla2xxx/qla_os.c
index d4b484c0fd9d..253f802605d6 100644
--- a/drivers/scsi/qla2xxx/qla_os.c
+++ b/drivers/scsi/qla2xxx/qla_os.c
@@ -6459,9 +6459,10 @@ void qla24xx_process_purex_rdp(struct scsi_qla_host *vha,
  void
  qla24xx_free_purex_item(struct purex_item *item)
  {
-       if (item == &item->vha->default_item)
+       if (item == &item->vha->default_item) {
                 memset(&item->vha->default_item, 0, sizeof(struct purex_item));
-       else
+               memset(&item->vha->__default_item_iocb, 0, QLA_DEFAULT_PAYLOAD_SIZE);
+       } else
                 kfree(item);

Thanks
-Gustavo