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

["Hsu, Chiahao" <andyhsu@xxxxxxxxxx>]

On 25.02.21, 13:29, "Hsu, Chiahao" <andyhsu@xxxxxxxxxx> 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@xxxxxxxxxx>
    ---
     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.