Re: [PATCH 1/2] xen-netback: add module parameter to disable ctrl-ring

[Paul Durrant <xadimgnik@gmail.com>]

On 09/03/2021 14:10, Hsu, Chiahao wrote:
> On 25.02.21, 13:29, "Hsu, Chiahao" <andyhsu@amazon.com> wrote:
> 
>      In order to support live migration of guests between kernels
>      that do and do not support 'feature-ctrl-ring', we add a
>      module parameter that allows the feature to be disabled
>      at run time, instead of using hardcode value.
>      The default value is enable.
> 
>      Signed-off-by: ChiaHao Hsu <andyhsu@amazon.com>

You should directly CC maintainers, and also I don't see netdev in the 
To list... Did you send it there? I suspect not, since I don't see 
'net-next' in the prefix.

   Paul

>      ---
>       drivers/net/xen-netback/common.h  |  2 ++
>       drivers/net/xen-netback/netback.c |  6 ++++++
>       drivers/net/xen-netback/xenbus.c  | 13 ++++++++-----
>       3 files changed, 16 insertions(+), 5 deletions(-)
> 
>      diff --git a/drivers/net/xen-netback/common.h b/drivers/net/xen-netback/common.h
>      index 4a16d6e33c09..bfb7a3054917 100644
>      --- a/drivers/net/xen-netback/common.h
>      +++ b/drivers/net/xen-netback/common.h
>      @@ -276,6 +276,7 @@ struct backend_info {
>       	u8 have_hotplug_status_watch:1;
> 
>       	const char *hotplug_script;
>      +	bool ctrl_ring_enabled;
>       };
> 
>       struct xenvif {
>      @@ -413,6 +414,7 @@ static inline pending_ring_idx_t nr_pending_reqs(struct xenvif_queue *queue)
> 
>       irqreturn_t xenvif_interrupt(int irq, void *dev_id);
> 
>      +extern bool control_ring;
>       extern bool separate_tx_rx_irq;
>       extern bool provides_xdp_headroom;
> 
>      diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
>      index e5c73f819662..20d858f0456a 100644
>      --- a/drivers/net/xen-netback/netback.c
>      +++ b/drivers/net/xen-netback/netback.c
>      @@ -48,6 +48,12 @@
> 
>       #include <asm/xen/hypercall.h>
> 
>      +/* Provide an option to disable control ring which is used to pass
>      + * large quantities of data from frontend to backend.
>      + */
>      +bool control_ring = true;
>      +module_param(control_ring, bool, 0644);
>      +
>       /* Provide an option to disable split event channels at load time as
>        * event channels are limited resource. Split event channels are
>        * enabled by default.
>      diff --git a/drivers/net/xen-netback/xenbus.c b/drivers/net/xen-netback/xenbus.c
>      index a5439c130130..8a9169cff9c5 100644
>      --- a/drivers/net/xen-netback/xenbus.c
>      +++ b/drivers/net/xen-netback/xenbus.c
>      @@ -1123,11 +1123,14 @@ static int netback_probe(struct xenbus_device *dev,
>       	if (err)
>       		pr_debug("Error writing multi-queue-max-queues\n");
> 
>      -	err = xenbus_printf(XBT_NIL, dev->nodename,
>      -			    "feature-ctrl-ring",
>      -			    "%u", true);
>      -	if (err)
>      -		pr_debug("Error writing feature-ctrl-ring\n");
>      +	be->ctrl_ring_enabled = READ_ONCE(control_ring);
>      +	if (be->ctrl_ring_enabled) {
>      +		err = xenbus_printf(XBT_NIL, dev->nodename,
>      +				    "feature-ctrl-ring",
>      +				    "%u", true);
>      +		if (err)
>      +			pr_debug("Error writing feature-ctrl-ring\n");
>      +	}
> 
>       	backend_switch_state(be, XenbusStateInitWait);
> 
>      --
>      2.23.3
> 
> Gentle ping.
>