linux-kernel - Re: [PATCH 12/12] Initialize xenbus device structs with ENODEV as default state

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Date:	Tue, 18 May 2010 11:28:30 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
CC:	linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com,
	Don Dutile <ddutile@...hat.com>,
	Sheng Yang <sheng@...ux.intel.com>
Subject: Re: [PATCH 12/12] Initialize xenbus device structs with ENODEV as
 default state

On 05/18/2010 03:23 AM, Stefano Stabellini wrote:
> From: Don Dutile <ddutile@...hat.com>
>
> this way if xenbus isn't configured in a FV xen guest,
>   

What does "FV" mean here?  Do you mean HVM?

> loading pv drivers (like netfront) won't crash the guest.
>   

No, this is way too hacky.  Is the issue that xenbus can't handle
drivers registering with it before it has been initialized?  How does
pci, usb, etc bus implementations deal with this?

    J

> Signed-off-by: Don Dutile <ddutile@...hat.com>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@...citrix.com>
> ---
>  drivers/xen/xenbus/xenbus_probe.c |   29 +++++++++++++++++++++++++----
>  drivers/xen/xenbus/xenbus_probe.h |    1 +
>  2 files changed, 26 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
> index f83e083..5e8dae6 100644
> --- a/drivers/xen/xenbus/xenbus_probe.c
> +++ b/drivers/xen/xenbus/xenbus_probe.c
> @@ -188,6 +188,11 @@ static struct xen_bus_type xenbus_frontend = {
>  	.levels = 2, 		/* device/type/<id> */
>  	.get_bus_id = frontend_bus_id,
>  	.probe = xenbus_probe_frontend,
> +	/* 
> +	 * to ensure loading pv-on-hvm drivers on FV guest
> +	 * doesn't blow up trying to use uninit'd xenbus.
> +	 */
> +	.error = -ENODEV,
>  	.bus = {
>  		.name      = "xen",
>  		.match     = xenbus_match,
> @@ -352,6 +357,9 @@ int xenbus_register_driver_common(struct xenbus_driver *drv,
>  				  struct module *owner,
>  				  const char *mod_name)
>  {
> +	if (bus->error)
> +		return bus->error;
> +
>  	drv->driver.name = drv->name;
>  	drv->driver.bus = &bus->bus;
>  	drv->driver.owner = owner;
> @@ -484,8 +492,12 @@ int xenbus_probe_node(struct xen_bus_type *bus,
>  	struct xenbus_device *xendev;
>  	size_t stringlen;
>  	char *tmpstring;
> +	enum xenbus_state state;
> +
> +	if (bus->error)
> +		return bus->error;
>  
> -	enum xenbus_state state = xenbus_read_driver_state(nodename);
> +	state = xenbus_read_driver_state(nodename);
>  
>  	if (state != XenbusStateInitialising) {
>  		/* Device is not new, so ignore it.  This can happen if a
> @@ -593,6 +605,9 @@ int xenbus_probe_devices(struct xen_bus_type *bus)
>  	char **dir;
>  	unsigned int i, dir_n;
>  
> +	if (bus->error)
> +		return bus->error;
> +
>  	dir = xenbus_directory(XBT_NIL, bus->root, "", &dir_n);
>  	if (IS_ERR(dir))
>  		return PTR_ERR(dir);
> @@ -636,7 +651,7 @@ void xenbus_dev_changed(const char *node, struct xen_bus_type *bus)
>  	char type[XEN_BUS_ID_SIZE];
>  	const char *p, *root;
>  
> -	if (char_count(node, '/') < 2)
> +	if (bus->error || char_count(node, '/') < 2)
>  		return;
>  
>  	exists = xenbus_exists(XBT_NIL, node, "");
> @@ -829,8 +844,8 @@ int xenbus_probe_init(void)
>  	DPRINTK("");
>  
>  	/* Register ourselves with the kernel bus subsystem */
> -	err = bus_register(&xenbus_frontend.bus);
> -	if (err)
> +	xenbus_frontend.error = bus_register(&xenbus_frontend.bus);
> +	if (xenbus_frontend.error)
>  		goto out_error;
>  
>  	err = xenbus_backend_bus_register();
> @@ -923,6 +938,9 @@ static int is_device_connecting(struct device *dev, void *data)
>  
>  static int exists_connecting_device(struct device_driver *drv)
>  {
> +	if (xenbus_frontend.error)
> +		return xenbus_frontend.error;
> +
>  	return bus_for_each_dev(&xenbus_frontend.bus, NULL, drv,
>  				is_device_connecting);
>  }
> @@ -1002,6 +1020,9 @@ static void wait_for_devices(struct xenbus_driver *xendrv)
>  #ifndef MODULE
>  static int __init boot_wait_for_devices(void)
>  {
> +	if (!xenbus_frontend.error)
> +		return xenbus_frontend.error;
> +
>  	ready_to_wait_for_devices = 1;
>  	wait_for_devices(NULL);
>  	return 0;
> diff --git a/drivers/xen/xenbus/xenbus_probe.h b/drivers/xen/xenbus/xenbus_probe.h
> index 6c5e318..15febe4 100644
> --- a/drivers/xen/xenbus/xenbus_probe.h
> +++ b/drivers/xen/xenbus/xenbus_probe.h
> @@ -53,6 +53,7 @@ static inline void xenbus_backend_bus_unregister(void) {}
>  struct xen_bus_type
>  {
>  	char *root;
> +	int error;
>  	unsigned int levels;
>  	int (*get_bus_id)(char bus_id[XEN_BUS_ID_SIZE], const char *nodename);
>  	int (*probe)(const char *type, const char *dir);
>   

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