cciss: detect bad alignment of scsi commands at build time

cciss: detect bad alignment of scsi commands at build time
Incidentally fix some nearby c++ style comments.

Signed-off-by: Stephen M. Cameron <scameron@beardog.cce.hp.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

3 files changed, 15 insertions, 8 deletions

diff --git a/drivers/block/cciss.c b/drivers/block/cciss.c
index a29e69418a03..cd8c7c20b1c3 100644
--- a/drivers/block/cciss.c
+++ b/drivers/block/cciss.c
@@ -4496,7 +4496,7 @@ static int __init cciss_init(void)
          * boundary. Given that we use pci_alloc_consistent() to allocate an
          * array of them, the size must be a multiple of 8 bytes.
          */
-        BUILD_BUG_ON(sizeof(CommandList_struct) % 8);
+        BUILD_BUG_ON(sizeof(CommandList_struct) % COMMANDLIST_ALIGNMENT);
 
         printk(KERN_INFO DRIVER_NAME "\n");
 
diff --git a/drivers/block/cciss_cmd.h b/drivers/block/cciss_cmd.h
index 515c9f03c201..e624ff959cb6 100644
--- a/drivers/block/cciss_cmd.h
+++ b/drivers/block/cciss_cmd.h
@@ -167,10 +167,13 @@ typedef struct _SGDescriptor_struct {
 #define CMD_MSG_TIMEOUT 0x05
 #define CMD_MSG_STALE   0xff
 
-/* This structure needs to be divisible by 8 for new
- * indexing method.  PAD_32 and PAD_64 can be adjusted
- * independently as needed for 32-bit and 64-bits systems.
+/* This structure needs to be divisible by COMMANDLIST_ALIGNMENT
+ * because low bits of the address are used to to indicate that
+ * whether the tag contains an index or an address.  PAD_32 and
+ * PAD_64 can be adjusted independently as needed for 32-bit
+ * and 64-bits systems.
  */
+#define COMMANDLIST_ALIGNMENT (8)
 #define IS_64_BIT ((sizeof(long) - 4)/4)
 #define IS_32_BIT (!IS_64_BIT)
 #define PAD_32 (0)
diff --git a/drivers/block/cciss_scsi.c b/drivers/block/cciss_scsi.c
index 5d0e46dc3632..f203606faaff 100644
--- a/drivers/block/cciss_scsi.c
+++ b/drivers/block/cciss_scsi.c
@@ -93,11 +93,15 @@ static struct scsi_host_template cciss_driver_template = {
 };
 
 #pragma pack(1)
+
+#define SCSI_PAD_32 4
+#define SCSI_PAD_64 4
+
 struct cciss_scsi_cmd_stack_elem_t {
         CommandList_struct cmd;
         ErrorInfo_struct Err;
         __u32 busaddr;
-        __u32 pad;
+        u8 pad[IS_32_BIT * SCSI_PAD_32 + IS_64_BIT * SCSI_PAD_64];
 };
 
 #pragma pack()
@@ -202,9 +206,9 @@ scsi_cmd_stack_setup(int ctlr, struct cciss_scsi_adapter_data_t *sa)
         stk = &sa->cmd_stack; 
         size = sizeof(struct cciss_scsi_cmd_stack_elem_t) * CMD_STACK_SIZE;
 
-        // pci_alloc_consistent guarantees 32-bit DMA address will
-        // be used
-
+        /* Check alignment, see cciss_cmd.h near CommandList_struct def. */
+        BUILD_BUG_ON((sizeof(*stk->pool) % COMMANDLIST_ALIGNMENT) != 0);
+        /* pci_alloc_consistent guarantees 32-bit DMA address will be used */
         stk->pool = (struct cciss_scsi_cmd_stack_elem_t *)
                 pci_alloc_consistent(hba[ctlr]->pdev, size, &stk->cmd_pool_handle);