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SubjectRe: [PATCH v2 04/18] xen/pvcalls: xenbus state handling
Date
On 05/19/2017 07:22 PM, Stefano Stabellini wrote:
> Introduce the code to handle xenbus state changes.
>
> Implement the probe function for the pvcalls backend. Write the
> supported versions, max-page-order and function-calls nodes to xenstore,
> as required by the protocol.
>
> Introduce stub functions for disconnecting/connecting to a frontend.
>
> Signed-off-by: Stefano Stabellini <stefano@aporeto.com>
> CC: boris.ostrovsky@oracle.com
> CC: jgross@suse.com
> ---
> drivers/xen/pvcalls-back.c | 135 +++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 135 insertions(+)
>
> diff --git a/drivers/xen/pvcalls-back.c b/drivers/xen/pvcalls-back.c
> index 9044cf2..b4da138 100644
> --- a/drivers/xen/pvcalls-back.c
> +++ b/drivers/xen/pvcalls-back.c
> @@ -25,20 +25,155 @@
> #include <xen/xenbus.h>
> #include <xen/interface/io/pvcalls.h>
>
> +#define PVCALLS_VERSIONS "1"

Shouldn't this be in a header file that will be shared with frontends?

> +#define MAX_RING_ORDER XENBUS_MAX_RING_GRANT_ORDER
> +
> struct pvcalls_back_global {
> struct list_head frontends;
> struct semaphore frontends_lock;
> } pvcalls_back_global;
>
> +static int backend_connect(struct xenbus_device *dev)
> +{
> + return 0;
> +}
> +
> +static int backend_disconnect(struct xenbus_device *dev)
> +{
> + return 0;
> +}
> +
> static int pvcalls_back_probe(struct xenbus_device *dev,
> const struct xenbus_device_id *id)
> {
> + int err;
> +
> + err = xenbus_printf(XBT_NIL, dev->nodename, "versions", "%s",
> + PVCALLS_VERSIONS);
> + if (err) {
> + pr_warn("%s write out 'version' failed\n", __func__);
> + return -EINVAL;

err?

> + }
> +
> + err = xenbus_printf(XBT_NIL, dev->nodename, "max-page-order", "%u",
> + MAX_RING_ORDER);
> + if (err) {
> + pr_warn("%s write out 'max-page-order' failed\n", __func__);
> + return err;
> + }
> +
> + /* "1" means socket, connect, release, bind, listen, accept and poll*/

This comment is obsolete, or at least should refer to
XENBUS_FUNCTIONS_CALLS (and is missing a space at the end).

> + err = xenbus_printf(XBT_NIL, dev->nodename, "function-calls",
> + XENBUS_FUNCTIONS_CALLS);
> + if (err) {
> + pr_warn("%s write out 'function-calls' failed\n", __func__);
> + return err;
> + }


In case of errors we will end up with all previous entries. I think this
should be done as a transaction which would be aborted in case of an error.

> +
> + err = xenbus_switch_state(dev, XenbusStateInitWait);
> + if (err)
> + return err;


Not sure what to do on an error here (wrt xenstore entries).
xenbus_switch_state() itself uses transactions. Are we allowed to have
nested transactions?

OTOH, xenbus_switch_state() never returns an error, at least now. In
fact, in most cases we ignore return value.


-boris


> +
> return 0;
> }
>
>

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