Re: [PATCH v2 04/18] xen/pvcalls: xenbus state handling

[Stefano Stabellini]

On Thu, 25 May 2017, Boris Ostrovsky wrote:
> 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 
> > CC: boris.ostrov...@oracle.com
> > CC: jgr...@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 
> >  #include 
> >  
> > +#define PVCALLS_VERSIONS "1"
> 
> Shouldn't this be in a header file that will be shared with frontends?

I don't think it should: different backends could implement a different
pvcalls version. There is an handshake mechanism to agree on a version
of the protocol to use. It is probably not a good idea to expose this
specific version in the generic pvcalls header.


> > +#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?

OK


> > +   }
> > +
> > +   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 This comment is obsolete, or at least should refer to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).

OK


> > +   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.

OK


> > +
> > +   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.

I don't think we can have nested transactions. For simplicity, I'll
ignore errors from xenbus_switch_state.

Re: [PATCH v2 04/18] xen/pvcalls: xenbus state handling

[Stefano Stabellini]

On Thu, 25 May 2017, Boris Ostrovsky wrote:
> 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 
> > CC: boris.ostrov...@oracle.com
> > CC: jgr...@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 
> >  #include 
> >  
> > +#define PVCALLS_VERSIONS "1"
> 
> Shouldn't this be in a header file that will be shared with frontends?

I don't think it should: different backends could implement a different
pvcalls version. There is an handshake mechanism to agree on a version
of the protocol to use. It is probably not a good idea to expose this
specific version in the generic pvcalls header.


> > +#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?

OK


> > +   }
> > +
> > +   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).

OK


> > +   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.

OK


> > +
> > +   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.

I don't think we can have nested transactions. For simplicity, I'll
ignore errors from xenbus_switch_state.

Re: [PATCH v2 04/18] xen/pvcalls: xenbus state handling

[Boris Ostrovsky]

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 
> CC: boris.ostrov...@oracle.com
> CC: jgr...@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 
>  #include 
>  
> +#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;
>  }
>  
>

Re: [PATCH v2 04/18] xen/pvcalls: xenbus state handling

[Boris Ostrovsky]

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 
> CC: boris.ostrov...@oracle.com
> CC: jgr...@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 
>  #include 
>  
> +#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;
>  }
>  
>

[PATCH v2 04/18] xen/pvcalls: xenbus state handling

[Stefano Stabellini]

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 
CC: boris.ostrov...@oracle.com
CC: jgr...@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 
 #include 
 
+#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;
+
+   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 = 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*/
+   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;
+   }
+
+   err = xenbus_switch_state(dev, XenbusStateInitWait);
+   if (err)
+   return err;
+
return 0;
 }
 
+static void set_backend_state(struct xenbus_device *dev,
+ enum xenbus_state state)
+{
+   while (dev->state != state) {
+   switch (dev->state) {
+   case XenbusStateClosed:
+   switch (state) {
+   case XenbusStateInitWait:
+   case XenbusStateConnected:
+   xenbus_switch_state(dev, XenbusStateInitWait);
+   break;
+   case XenbusStateClosing:
+   xenbus_switch_state(dev, XenbusStateClosing);
+   break;
+   default:
+   __WARN();
+   }
+   break;
+   case XenbusStateInitWait:
+   case XenbusStateInitialised:
+   switch (state) {
+   case XenbusStateConnected:
+   backend_connect(dev);
+   xenbus_switch_state(dev, XenbusStateConnected);
+   break;
+   case XenbusStateClosing:
+   case XenbusStateClosed:
+   xenbus_switch_state(dev, XenbusStateClosing);
+   break;
+   default:
+   __WARN();
+   }
+   break;
+   case XenbusStateConnected:
+   switch (state) {
+   case XenbusStateInitWait:
+   case XenbusStateClosing:
+   case XenbusStateClosed:
+   down(_back_global.frontends_lock);
+   backend_disconnect(dev);
+   up(_back_global.frontends_lock);
+   xenbus_switch_state(dev, XenbusStateClosing);
+   break;
+   default:
+   __WARN();
+   }
+   break;
+   case XenbusStateClosing:
+   switch (state) {
+   case XenbusStateInitWait:
+   case XenbusStateConnected:
+   case XenbusStateClosed:
+   xenbus_switch_state(dev, XenbusStateClosed);
+   break;
+   default:
+   __WARN();
+   }
+   break;
+   default:
+   __WARN();
+   }
+   }
+}
+
 static void pvcalls_back_changed(struct 

[PATCH v2 04/18] xen/pvcalls: xenbus state handling

[Stefano Stabellini]

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 
CC: boris.ostrov...@oracle.com
CC: jgr...@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 
 #include 
 
+#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;
+
+   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 = 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*/
+   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;
+   }
+
+   err = xenbus_switch_state(dev, XenbusStateInitWait);
+   if (err)
+   return err;
+
return 0;
 }
 
+static void set_backend_state(struct xenbus_device *dev,
+ enum xenbus_state state)
+{
+   while (dev->state != state) {
+   switch (dev->state) {
+   case XenbusStateClosed:
+   switch (state) {
+   case XenbusStateInitWait:
+   case XenbusStateConnected:
+   xenbus_switch_state(dev, XenbusStateInitWait);
+   break;
+   case XenbusStateClosing:
+   xenbus_switch_state(dev, XenbusStateClosing);
+   break;
+   default:
+   __WARN();
+   }
+   break;
+   case XenbusStateInitWait:
+   case XenbusStateInitialised:
+   switch (state) {
+   case XenbusStateConnected:
+   backend_connect(dev);
+   xenbus_switch_state(dev, XenbusStateConnected);
+   break;
+   case XenbusStateClosing:
+   case XenbusStateClosed:
+   xenbus_switch_state(dev, XenbusStateClosing);
+   break;
+   default:
+   __WARN();
+   }
+   break;
+   case XenbusStateConnected:
+   switch (state) {
+   case XenbusStateInitWait:
+   case XenbusStateClosing:
+   case XenbusStateClosed:
+   down(_back_global.frontends_lock);
+   backend_disconnect(dev);
+   up(_back_global.frontends_lock);
+   xenbus_switch_state(dev, XenbusStateClosing);
+   break;
+   default:
+   __WARN();
+   }
+   break;
+   case XenbusStateClosing:
+   switch (state) {
+   case XenbusStateInitWait:
+   case XenbusStateConnected:
+   case XenbusStateClosed:
+   xenbus_switch_state(dev, XenbusStateClosed);
+   break;
+   default:
+   __WARN();
+   }
+   break;
+   default:
+   __WARN();
+   }
+   }
+}
+
 static void pvcalls_back_changed(struct xenbus_device *dev,