[v2,2/3] xen: slightly simplify bufioreq handling

Commit Message

Jan Beulich Nov. 25, 2016, 10:06 a.m. UTC

There's no point setting fields always receiving the same value on each
iteration, as handle_ioreq() doesn't alter them anyway. Set state and
count once ahead of the loop, drop the redundant clearing of
data_is_ptr, and avoid the meaningless setting of df altogether.

Also avoid doing an unsigned long calculation of size when the field to
be initialized is only 32 bits wide (and the shift value in the range
0...3).

Signed-off-by: Jan Beulich <[e-mail]>
Reviewed-by: Paul Durrant <[e-mail]>

Comments

Stefano Stabellini Nov. 28, 2016, 7:24 p.m. UTC | #1

On Fri, 25 Nov 2016, Jan Beulich wrote:
> There's no point setting fields always receiving the same value on each
> iteration, as handle_ioreq() doesn't alter them anyway. Set state and
> count once ahead of the loop, drop the redundant clearing of
> data_is_ptr, and avoid the meaningless setting of df altogether.
> 
> Also avoid doing an unsigned long calculation of size when the field to
> be initialized is only 32 bits wide (and the shift value in the range
> 0...3).
> 
> Signed-off-by: Jan Beulich <[e-mail]>
> Reviewed-by: Paul Durrant <[e-mail]>

Reviewed-by: Stefano Stabellini <[e-mail]>


> --- a/xen-hvm.c
> +++ b/xen-hvm.c
> @@ -995,6 +995,8 @@ static int handle_buffered_iopage(XenIOS
>      }
>  
>      memset(&req, 0x00, sizeof(req));
> +    req.state = STATE_IOREQ_READY;
> +    req.count = 1;
>  
>      for (;;) {
>          uint32_t rdptr = buf_page->read_pointer, wrptr;
> @@ -1009,15 +1011,11 @@ static int handle_buffered_iopage(XenIOS
>              break;
>          }
>          buf_req = &buf_page->buf_ioreq[rdptr % IOREQ_BUFFER_SLOT_NUM];
> -        req.size = 1UL << buf_req->size;
> -        req.count = 1;
> +        req.size = 1U << buf_req->size;
>          req.addr = buf_req->addr;
>          req.data = buf_req->data;
> -        req.state = STATE_IOREQ_READY;
>          req.dir = buf_req->dir;
> -        req.df = 1;
>          req.type = buf_req->type;
> -        req.data_is_ptr = 0;
>          xen_rmb();
>          qw = (req.size == 8);
>          if (qw) {
> @@ -1032,6 +1030,13 @@ static int handle_buffered_iopage(XenIOS
>  
>          handle_ioreq(state, &req);
>  
> +        /* Only req.data may get updated by handle_ioreq(), albeit even that
> +         * should not happen as such data would never make it to the guest.
> +         */
> +        assert(req.state == STATE_IOREQ_READY);
> +        assert(req.count == 1);
> +        assert(!req.data_is_ptr);
> +
>          atomic_add(&buf_page->read_pointer, qw + 1);
>      }
>  
> 
> 
>

Patch

--- a/xen-hvm.c
+++ b/xen-hvm.c
@@ -995,6 +995,8 @@  static int handle_buffered_iopage(XenIOS
     }
 
     memset(&req, 0x00, sizeof(req));
+    req.state = STATE_IOREQ_READY;
+    req.count = 1;
 
     for (;;) {
         uint32_t rdptr = buf_page->read_pointer, wrptr;
@@ -1009,15 +1011,11 @@  static int handle_buffered_iopage(XenIOS
             break;
         }
         buf_req = &buf_page->buf_ioreq[rdptr % IOREQ_BUFFER_SLOT_NUM];
-        req.size = 1UL << buf_req->size;
-        req.count = 1;
+        req.size = 1U << buf_req->size;
         req.addr = buf_req->addr;
         req.data = buf_req->data;
-        req.state = STATE_IOREQ_READY;
         req.dir = buf_req->dir;
-        req.df = 1;
         req.type = buf_req->type;
-        req.data_is_ptr = 0;
         xen_rmb();
         qw = (req.size == 8);
         if (qw) {
@@ -1032,6 +1030,13 @@  static int handle_buffered_iopage(XenIOS
 
         handle_ioreq(state, &req);
 
+        /* Only req.data may get updated by handle_ioreq(), albeit even that
+         * should not happen as such data would never make it to the guest.
+         */
+        assert(req.state == STATE_IOREQ_READY);
+        assert(req.count == 1);
+        assert(!req.data_is_ptr);
+
         atomic_add(&buf_page->read_pointer, qw + 1);
     }