linux-kernel - Re: [PATCH v6 04/18] xen/pvcalls: xenbus state handling

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Message-ID: <2dd8d8e1-4fc4-3d9e-0b74-b1704ac5e658@suse.com>
Date:   Tue, 4 Jul 2017 10:03:07 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Stefano Stabellini <sstabellini@...nel.org>,
        xen-devel@...ts.xen.org
Cc:     linux-kernel@...r.kernel.org, boris.ostrovsky@...cle.com,
        Stefano Stabellini <stefano@...reto.com>
Subject: Re: [PATCH v6 04/18] xen/pvcalls: xenbus state handling

On 03/07/17 23:08, 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@...reto.com>
> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> CC: boris.ostrovsky@...cle.com
> CC: jgross@...e.com
> ---
>  drivers/xen/pvcalls-back.c | 152 +++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 152 insertions(+)
> 
> diff --git a/drivers/xen/pvcalls-back.c b/drivers/xen/pvcalls-back.c
> index 9044cf2..7bce750 100644
> --- a/drivers/xen/pvcalls-back.c
> +++ b/drivers/xen/pvcalls-back.c
> @@ -25,20 +25,172 @@
>  #include <xen/xenbus.h>
>  #include <xen/interface/io/pvcalls.h>
>  
> +#define PVCALLS_VERSIONS "1"
> +#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, abort;
> +	struct xenbus_transaction xbt;
> +
> +again:
> +	abort = 1;
> +
> +	err = xenbus_transaction_start(&xbt);
> +	if (err) {
> +		pr_warn("%s cannot create xenstore transaction\n", __func__);
> +		return err;
> +	}
> +
> +	err = xenbus_printf(xbt, dev->nodename, "versions", "%s",
> +			    PVCALLS_VERSIONS);
> +	if (err) {
> +		pr_warn("%s write out 'version' failed\n", __func__);

s/version/versions/ ?

> +		goto abort;
> +	}
> +
> +	err = xenbus_printf(xbt, dev->nodename, "max-page-order", "%u",
> +			    MAX_RING_ORDER);
> +	if (err) {
> +		pr_warn("%s write out 'max-page-order' failed\n", __func__);
> +		goto abort;
> +	}
> +
> +	err = xenbus_printf(xbt, dev->nodename, "function-calls",
> +			    XENBUS_FUNCTIONS_CALLS);
> +	if (err) {
> +		pr_warn("%s write out 'function-calls' failed\n", __func__);
> +		goto abort;
> +	}
> +
> +	abort = 0;
> +abort:
> +	err = xenbus_transaction_end(xbt, abort);
> +	if (err) {
> +		if (err == -EAGAIN && !abort)

Hmm, while I don't think xenbus_transaction_end() will ever
return -EAGAIN in the abort case I'm not sure you should limit
the retry loop to the non-abort case.

> +			goto again;
> +		pr_warn("%s cannot complete xenstore transaction\n", __func__);
> +		return err;
> +	}
> +
> +	xenbus_switch_state(dev, XenbusStateInitWait);

I don't think you should switch state in case of abort set, no?


Juergen