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

[Stefano Stabellini]

Many thanks for all the reviews!

On Tue, 4 Jul 2017, Juergen Gross wrote:
> 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 
> > Reviewed-by: Boris Ostrovsky 
> > CC: boris.ostrov...@oracle.com
> > CC: jgr...@suse.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 
> >  #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, abort;
> > +   struct xenbus_transaction xbt;
> > +
> > +again:
> > +   abort = 1;
> > +
> > +   err = xenbus_transaction_start();
> > +   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/ ?

OK


> > +   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.

Realistically, if we want to abort and get -EAGAIN, the best thing to do
is to get out (current behavior). The other option would be to keep
issuing xenbus_transaction_end(xbr, 1) in a loop until it succeeds, but
it seems more fragile to me.


> > +   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?

Good point, I'll change that.

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

[Stefano Stabellini]

Many thanks for all the reviews!

On Tue, 4 Jul 2017, Juergen Gross wrote:
> 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 
> > Reviewed-by: Boris Ostrovsky 
> > CC: boris.ostrov...@oracle.com
> > CC: jgr...@suse.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 
> >  #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, abort;
> > +   struct xenbus_transaction xbt;
> > +
> > +again:
> > +   abort = 1;
> > +
> > +   err = xenbus_transaction_start();
> > +   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/ ?

OK


> > +   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.

Realistically, if we want to abort and get -EAGAIN, the best thing to do
is to get out (current behavior). The other option would be to keep
issuing xenbus_transaction_end(xbr, 1) in a loop until it succeeds, but
it seems more fragile to me.


> > +   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?

Good point, I'll change that.

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

[Juergen Gross]

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 
> Reviewed-by: Boris Ostrovsky 
> CC: boris.ostrov...@oracle.com
> CC: jgr...@suse.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 
>  #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, abort;
> + struct xenbus_transaction xbt;
> +
> +again:
> + abort = 1;
> +
> + err = xenbus_transaction_start();
> + 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

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

[Juergen Gross]

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 
> Reviewed-by: Boris Ostrovsky 
> CC: boris.ostrov...@oracle.com
> CC: jgr...@suse.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 
>  #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, abort;
> + struct xenbus_transaction xbt;
> +
> +again:
> + abort = 1;
> +
> + err = xenbus_transaction_start();
> + 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

[PATCH v6 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 
Reviewed-by: Boris Ostrovsky 
CC: boris.ostrov...@oracle.com
CC: jgr...@suse.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 
 #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, abort;
+   struct xenbus_transaction xbt;
+
+again:
+   abort = 1;
+
+   err = xenbus_transaction_start();
+   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__);
+   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)
+   goto again;
+   pr_warn("%s cannot complete xenstore transaction\n", __func__);
+   return err;
+   }
+
+   xenbus_switch_state(dev, XenbusStateInitWait);
+
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:
+

[PATCH v6 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 
Reviewed-by: Boris Ostrovsky 
CC: boris.ostrov...@oracle.com
CC: jgr...@suse.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 
 #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, abort;
+   struct xenbus_transaction xbt;
+
+again:
+   abort = 1;
+
+   err = xenbus_transaction_start();
+   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__);
+   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)
+   goto again;
+   pr_warn("%s cannot complete xenstore transaction\n", __func__);
+   return err;
+   }
+
+   xenbus_switch_state(dev, XenbusStateInitWait);
+
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:
+