Re: [PATCH 3/4] virtio: console makes incorrect assumption about virtio API

[Amit Shah]

On (Tue) Mar 30 2010 [15:49:22], Rusty Russell wrote:
> The get_buf() API sets the second arg to the number of bytes *written*
> by the other side; in this case it should be zero as these are output buffers.
> 
> lguest gets this right (obviously kvm's console doesn't), resulting in
> continual buildup of console writes.
> 
> Signed-off-by: Rusty Russell 
> To: Amit Shah 

Acked-by: Amit Shah 

> ---
>  drivers/char/virtio_console.c |   10 +++---
>  1 file changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
> --- a/drivers/char/virtio_console.c
> +++ b/drivers/char/virtio_console.c
> @@ -415,20 +415,16 @@ static ssize_t send_buf(struct port *por
>   out_vq->vq_ops->kick(out_vq);
>  
>   if (ret < 0) {
> - len = 0;
> + in_count = 0;
>   goto fail;
>   }
>  
> - /*
> -  * Wait till the host acknowledges it pushed out the data we
> -  * sent. Also ensure we return to userspace the number of
> -  * bytes that were successfully consumed by the host.
> -  */
> + /* Wait till the host acknowledges it pushed out the data we sent. */
>   while (!out_vq->vq_ops->get_buf(out_vq, &len))
>   cpu_relax();
>  fail:
>   /* We're expected to return the amount of data we wrote */
> - return len;
> + return in_count;
>  }
>  
>  /*
> 

Amit
-- 
http://log.amitshah.net/
___
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linux-foundation.org/mailman/listinfo/virtualization

[PATCH 3/4] virtio: console makes incorrect assumption about virtio API

[Rusty Russell]

The get_buf() API sets the second arg to the number of bytes *written*
by the other side; in this case it should be zero as these are output buffers.

lguest gets this right (obviously kvm's console doesn't), resulting in
continual buildup of console writes.

Signed-off-by: Rusty Russell 
To: Amit Shah 
---
 drivers/char/virtio_console.c |   10 +++---
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -415,20 +415,16 @@ static ssize_t send_buf(struct port *por
out_vq->vq_ops->kick(out_vq);
 
if (ret < 0) {
-   len = 0;
+   in_count = 0;
goto fail;
}
 
-   /*
-* Wait till the host acknowledges it pushed out the data we
-* sent. Also ensure we return to userspace the number of
-* bytes that were successfully consumed by the host.
-*/
+   /* Wait till the host acknowledges it pushed out the data we sent. */
while (!out_vq->vq_ops->get_buf(out_vq, &len))
cpu_relax();
 fail:
/* We're expected to return the amount of data we wrote */
-   return len;
+   return in_count;
 }
 
 /*

___
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linux-foundation.org/mailman/listinfo/virtualization