[net-next,v6,03/10] net: create a dummy net_device allocator

Commit Message

Breno Leitao April 11, 2024, 1:59 p.m. UTC

It is impossible to use init_dummy_netdev together with alloc_netdev()
as the 'setup' argument.

This is because alloc_netdev() initializes some fields in the net_device
structure, and later init_dummy_netdev() memzero them all. This causes
some problems as reported here:

	https://lore.kernel.org/all/[e-mail]/

Split the init_dummy_netdev() function in two. Create a new function called
init_dummy_netdev_core() that does not memzero the net_device structure.
Then have init_dummy_netdev() memzero-ing and calling
init_dummy_netdev_core(), keeping the old behaviour.

init_dummy_netdev_core() is the new function that could be called as an
argument for alloc_netdev().

Also, create a helper to allocate and initialize dummy net devices,
leveraging init_dummy_netdev_core() as the setup argument. This function
basically simplify the allocation of dummy devices, by allocating and
initializing it. Freeing the device continue to be done through
free_netdev()

Suggested-by: Jakub Kicinski <[e-mail]>
Signed-off-by: Breno Leitao <[e-mail]>
Reviewed-by: Ido Schimmel <[e-mail]>
---
 include/linux/netdevice.h |  3 +++
 net/core/dev.c            | 54 ++++++++++++++++++++++++++-------------
 2 files changed, 39 insertions(+), 18 deletions(-)

Comments

Jakub Kicinski April 13, 2024, 2:16 a.m. UTC | #1

On Thu, 11 Apr 2024 06:59:27 -0700 Breno Leitao wrote:
> +/**
> + * alloc_netdev_dummy - Allocate and initialize a dummy net device.
> + * @sizeof_priv: size of private data to allocate space for
> + */
> +struct net_device *alloc_netdev_dummy(int sizeof_priv)

Sorry, one more round :)

We started using -Wall for kdoc (./scripts/kernel-doc -Wall $files)
recently and it now complains about missing return values...

Alexander Lobakin April 17, 2024, 10:51 a.m. UTC | #2

From: Jakub Kicinski <[e-mail]>
Date: Fri, 12 Apr 2024 19:16:26 -0700

> On Thu, 11 Apr 2024 06:59:27 -0700 Breno Leitao wrote:
>> +/**
>> + * alloc_netdev_dummy - Allocate and initialize a dummy net device.
>> + * @sizeof_priv: size of private data to allocate space for
>> + */
>> +struct net_device *alloc_netdev_dummy(int sizeof_priv)
> 
> Sorry, one more round :)
> 
> We started using -Wall for kdoc (./scripts/kernel-doc -Wall $files)
> recently and it now complains about missing return values...

Just FYI: kdoc accepts only this pattern:

 * @last_param: blah
 *
 * Return: blah

NOT

 * Returns: blah

neither

 * Returns blah

Only "Return: blah" with a blank newline between it and the last
argument (or extended description).

Thanks,
Olek

Johannes Berg April 17, 2024, 11:11 a.m. UTC | #3

On Wed, 2024-04-17 at 12:51 +0200, Alexander Lobakin wrote:
> Just FYI: kdoc accepts only this pattern:
> 
>  * @last_param: blah
>  *
>  * Return: blah
> 
> NOT
> 
>  * Returns: blah

Actually, it does accept that, the regex is "returns?". It's just
documented only as "Return" . IMHO it sometimes reads nicer as "Returns"
depending on how you phrase it, but ...

johannes

Alexander Lobakin April 17, 2024, 11:19 a.m. UTC | #4

From: Johannes Berg <[e-mail]>
Date: Wed, 17 Apr 2024 13:11:38 +0200

> On Wed, 2024-04-17 at 12:51 +0200, Alexander Lobakin wrote:
>> Just FYI: kdoc accepts only this pattern:
>>
>>  * @last_param: blah
>>  *
>>  * Return: blah
>>
>> NOT
>>
>>  * Returns: blah
> 
> Actually, it does accept that, the regex is "returns?". It's just

Hmm, I was sure I had warnings on "Returns:"... Not sure now.

> documented only as "Return" . IMHO it sometimes reads nicer as "Returns"
> depending on how you phrase it, but ...
> 
> johannes

Thanks,
Olek

Randy Dunlap April 17, 2024, 3:29 p.m. UTC | #5

On 4/17/24 4:19 AM, Alexander Lobakin wrote:
> From: Johannes Berg <[e-mail]>
> Date: Wed, 17 Apr 2024 13:11:38 +0200
> 
>> On Wed, 2024-04-17 at 12:51 +0200, Alexander Lobakin wrote:
>>> Just FYI: kdoc accepts only this pattern:
>>>
>>>  * @last_param: blah
>>>  *
>>>  * Return: blah
>>>
>>> NOT
>>>
>>>  * Returns: blah
>>
>> Actually, it does accept that, the regex is "returns?". It's just

ack (Return: is documented)

> Hmm, I was sure I had warnings on "Returns:"... Not sure now.
> 
Yes, either way is accepted.

> documented only as "Return" . IMHO it sometimes reads nicer as "Returns"
>> depending on how you phrase it, but ...

Patch

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index d45f330d083d..f849e7d110ed 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -4519,6 +4519,9 @@  static inline void netif_addr_unlock_bh(struct net_device *dev)
 
 void ether_setup(struct net_device *dev);
 
+/* Allocate dummy net_device */
+struct net_device *alloc_netdev_dummy(int sizeof_priv);
+
 /* Support for loadable net-drivers */
 struct net_device *alloc_netdev_mqs(int sizeof_priv, const char *name,
 				    unsigned char name_assign_type,
diff --git a/net/core/dev.c b/net/core/dev.c
index c74b42bc6888..417abfd12871 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -10414,25 +10414,12 @@  int register_netdevice(struct net_device *dev)
 }
 EXPORT_SYMBOL(register_netdevice);
 
-/**
- *	init_dummy_netdev	- init a dummy network device for NAPI
- *	@dev: device to init
- *
- *	This takes a network device structure and initializes the minimum
- *	amount of fields so it can be used to schedule NAPI polls without
- *	registering a full blown interface. This is to be used by drivers
- *	that need to tie several hardware interfaces to a single NAPI
- *	poll scheduler due to HW limitations.
+/* Initialize the core of a dummy net device.
+ * This is useful if you are calling this function after alloc_netdev(),
+ * since it does not memset the net_device fields.
  */
-void init_dummy_netdev(struct net_device *dev)
+static void init_dummy_netdev_core(struct net_device *dev)
 {
-	/* Clear everything. Note we don't initialize spinlocks
-	 * as they aren't supposed to be taken by any of the
-	 * NAPI code and this dummy netdev is supposed to be
-	 * only ever used for NAPI polls
-	 */
-	memset(dev, 0, sizeof(struct net_device));
-
 	/* make sure we BUG if trying to hit standard
 	 * register/unregister code path
 	 */
@@ -10453,8 +10440,28 @@  void init_dummy_netdev(struct net_device *dev)
 	 * its refcount.
 	 */
 }
-EXPORT_SYMBOL_GPL(init_dummy_netdev);
 
+/**
+ *	init_dummy_netdev	- init a dummy network device for NAPI
+ *	@dev: device to init
+ *
+ *	This takes a network device structure and initializes the minimum
+ *	amount of fields so it can be used to schedule NAPI polls without
+ *	registering a full blown interface. This is to be used by drivers
+ *	that need to tie several hardware interfaces to a single NAPI
+ *	poll scheduler due to HW limitations.
+ */
+void init_dummy_netdev(struct net_device *dev)
+{
+	/* Clear everything. Note we don't initialize spinlocks
+	 * as they aren't supposed to be taken by any of the
+	 * NAPI code and this dummy netdev is supposed to be
+	 * only ever used for NAPI polls
+	 */
+	memset(dev, 0, sizeof(struct net_device));
+	init_dummy_netdev_core(dev);
+}
+EXPORT_SYMBOL_GPL(init_dummy_netdev);
 
 /**
  *	register_netdev	- register a network device
@@ -11074,6 +11081,17 @@  void free_netdev(struct net_device *dev)
 }
 EXPORT_SYMBOL(free_netdev);
 
+/**
+ * alloc_netdev_dummy - Allocate and initialize a dummy net device.
+ * @sizeof_priv: size of private data to allocate space for
+ */
+struct net_device *alloc_netdev_dummy(int sizeof_priv)
+{
+	return alloc_netdev(sizeof_priv, "dummy#", NET_NAME_UNKNOWN,
+			    init_dummy_netdev_core);
+}
+EXPORT_SYMBOL_GPL(alloc_netdev_dummy);
+
 /**
  *	synchronize_net -  Synchronize with packet receive processing
  *