Received-SPF: pass (google.com: domain of linux-kernel+bounces-123122-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
Message-ID: <25a2266c-8ae4-41f5-9b80-beaf174043d1@intel.com>
Date: Thu, 28 Mar 2024 15:57:29 +0100
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH net-next] net: create a dummy net_device allocator
To: Jakub Kicinski <kuba@kernel.org>, Breno Leitao <leitao@debian.org>
CC: "David S. Miller" <davem@davemloft.net>, Eric Dumazet
	<edumazet@google.com>, Paolo Abeni <pabeni@redhat.com>,
	<quic_jjohnson@quicinc.com>, <kvalo@kernel.org>, <leon@kernel.org>,
	<dennis.dalessandro@cornelisnetworks.com>, Jiri Pirko <jiri@resnulli.us>,
	Simon Horman <horms@kernel.org>, Daniel Borkmann <daniel@iogearbox.net>,
	Lorenzo Bianconi <lorenzo@kernel.org>, Coco Li <lixiaoyan@google.com>, "open
 list:NETWORKING DRIVERS" <netdev@vger.kernel.org>, open list
	<linux-kernel@vger.kernel.org>
References: <20240327200809.512867-1-leitao@debian.org>
 <20240327161731.6b100cb8@kernel.org>
From: Alexander Lobakin <aleksander.lobakin@intel.com>
Content-Language: en-US
In-Reply-To: <20240327161731.6b100cb8@kernel.org>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 7bit
Precedence: bulk
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?SFIrOGFBclAxc0FKM1MxYnNCT3hleGUxVnVHdHk0QkhwM0ZBRkVBeEsyekNy?=
 =?utf-8?B?aGJpRm5FNVBkeGVsN0Jqd1kyRXI0Q2s5dFJwczBsUmFLTFpTUEQzSFoyQi9C?=
 =?utf-8?B?YTV3cTFDMmhsSmtIVEdxczlFU0loWlhuRjFyLzFyaml5ZjdhNlpvdG9heHpZ?=
 =?utf-8?B?MlB6ZXlOelRzMm5RWHpTYTNhdm10Szl4SnNldDlldjQvRUJrMlV0Vmo3ek03?=
 =?utf-8?B?ZDQxM2NPUml1YkVNQTdCUDI0c1JqWWhNTGVCVkxEQkdPdDgxTVc1RFZMcnBT?=
 =?utf-8?B?NElBOE9sak5mM1l4TEhOelp1WnoxSXc2SVU5NlJPZWtpdXdPSDd0ZWZnV2dJ?=
 =?utf-8?B?eDB0YnV0VGUyWVpNdDQvR3JtRkRzdUVoRXE0bkRCLzgrK2cvWGMzZG8zNHdN?=
 =?utf-8?B?RVFLdkhUN2NmN1lFaUkyQmo5Ylo0aG1DWVdzRksreExnUDNBUUNueW92eG5z?=
 =?utf-8?B?RTkzR0JWRlpVQmxNNjY4UDlab3ppRjNVT2tQejVMdmlGUjVwY3MwaXM2K20z?=
 =?utf-8?B?dFovRjRFL0NwTXZsWVVlckM1clpZeGR2a0lvendaalRsR3dBdHIrbTZRVWZn?=
 =?utf-8?B?MHdrcFpqTEMvRkwvdWpsMU9EMGlLM1JtZmlkWjBhL29ob3dPNVpUc3VkeUZV?=
 =?utf-8?B?dHBFMHR5ZmIzVGdZM1hHeE9xQTUya1B2WVByWjBHb1BFRWpqdmNkWWt0TDdS?=
 =?utf-8?B?TlhKUDNDU25EQzBKcC9RT3VieUc2RUhiT1dOcnNBcnZJYWVKakpRWVhaQWM4?=
 =?utf-8?B?aTNZZkp3VDkyOGRVaFFtNnRiSXZaM21WdjBDZVd1VVluWTJNdDhLYThMbjJ3?=
 =?utf-8?B?RVI2YzdlN0IxWHkxSllueXNXS1R2YlNRczBWbVRhWDNSbVo0R2NqZEsvZllz?=
 =?utf-8?B?MGVrbkh4eEswc0dROWVleVV1NUdnV3I1OUFWaXorTWJkYnNBN0lvSWtEWFJn?=
 =?utf-8?B?ZDJwOXhoNDV4bVFSZU5NMUltZzBCbWJncFBtUkplSndvT1FhaTA0bWZIYzMx?=
 =?utf-8?B?Zi9PenFXZkpyQzg2R2Z5S3E3czZmOUZzL3I5UkMzSVlSR3pXRWdudXU3TlNn?=
 =?utf-8?B?ZmFTMUFqRURaVGFZMFFGeWVqT1cvdDFnSUpUclBmWGV2aUcyTmViSjVkY1Ba?=
 =?utf-8?B?czcrK3UwWTNaMDBZOFgzbFJ6dUJHRFVzM244NDdIYkdpMmlWd0I0SWgrZGUz?=
 =?utf-8?B?STBlUFArUjRta21wY1ZHTUdZcTB1TXRiYW5uMEhjSnZmVGhBOTBrY1FhRTJR?=
 =?utf-8?B?bnhiR0FvanUydHZlQXFWU1BKTU1oU1lGaWJpamxQdnUzNVpnVytlN09hcFBK?=
 =?utf-8?B?c3RiWFhZUjVFVk1XTFY3YUordml5M212OFdxemVON0pKZ0cxNURvV1dTNzBP?=
 =?utf-8?B?eGFkWThpSlVRT0JGRlVWZXBPc09RR1JlbXc0cmdhOFpxbUJ4KzVZQmxhZnQ1?=
 =?utf-8?B?ajFEendpR21hdEI3UXlWUjcrcTBjNXNUUGk1MTdLdUNKMnZoZnNuZjdxMDB2?=
 =?utf-8?B?V2ROb3BBYm9hazJURTRobU1sd2p2a1dFK0ZLRmh2VFRyTG41VU44ckg1VGNS?=
 =?utf-8?B?WFZUOXVUUHNDanZQdUMxUGNYOE5xLzlhOUFnS3g4aldudDF3YktTRW9MdGFt?=
 =?utf-8?B?YWhMMmhwYWdwUkRrT0NRWnR0THA0c1VBaWJRVE56WXBCWEtOTjRjN3phaUV1?=
 =?utf-8?B?Skk0Zm90V3FXR3c5cW1FejZqUllDWkN6RjA0cUZZd2Z2WDJ0Z3lCVURkQnMy?=
 =?utf-8?B?MWFZM3M5Y29wUG5oT2srRU1UVmNxRlppNUNzOVlNaWYxbGpyUVJreGRjZy8y?=
 =?utf-8?B?REVEY1pZeVVtM2lDejFVMUI5Vm5YcVdUOXd2ZDRxbXk2MUtvaUE4U2NSQ09x?=
 =?utf-8?B?YlFCU2JqWVo0TjV2R1lac1ZnMXQ0NitYTUFTc1kyc3pBcGdnZzR0elhQREpH?=
 =?utf-8?B?Z0VSNU1qTzc3RkV2RkNXdlpXNmpzcFYySlJ5dFZDNFdrV25UU1plK1EyRjAr?=
 =?utf-8?B?QndTRGtKWUw4ek5yb1ZXNGRyUUZaeHdRcG5FUTluSUQ3L2t6MDBPVkgrRXBh?=
 =?utf-8?B?ZkVXcFkyY2VCZFQzcDc1T2VoSXNDZ2FGb2FicG5oTk8yYVVNVU5HWmpDZGcr?=
 =?utf-8?B?bU1mdzRKYVl0MnRObFRZbTdaakVrMU5zWmhELzBuS1ArK3BDVWFiYzl4L25J?=
 =?utf-8?B?M2c9PQ==?=
X-MS-Exchange-CrossTenant-Network-Message-Id: b2e3aeaa-23aa-41c4-a291-08dc4f377186
X-MS-Exchange-CrossTenant-AuthSource: DS0PR11MB8718.namprd11.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 Mar 2024 14:57:52.7598
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: 9PxfWDhcaupilirAgSrQng2wV6KhqAPjqebvMZGv094XswZ2m5Fmmu9iO63fEA5xk0rDEvD+2qgMhFK6jbAAKkihrjilfsgAlbsobxWrvEE=
X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ0PR11MB4894
X-OriginatorOrg: intel.com

From: Jakub Kicinski <kuba@kernel.org>
Date: Wed, 27 Mar 2024 16:17:31 -0700

> On Wed, 27 Mar 2024 13:08:04 -0700 Breno Leitao wrote:
>> 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/20240322082336.49f110cc@kernel.org/
>>
>> 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()
> 
> Ah, but you need to make it part of the series with some caller.
> Maybe convert all the ethernet ones?
> 
> $ git grep 'struct net_device [^*]*;' -- drivers/net/ethernet/
> drivers/net/ethernet/cavium/thunder/thunder_bgx.c:      struct net_device       netdev;
> drivers/net/ethernet/marvell/prestera/prestera_rxtx.c:  struct net_device napi_dev;
> drivers/net/ethernet/microchip/vcap/vcap_api_debugfs_kunit.c:static struct net_device test_netdev = {};
> drivers/net/ethernet/microchip/vcap/vcap_api_kunit.c:static struct net_device test_netdev = {};

There are much more of them unfortunately. Pretty much every user of
init_dummy_netdev()[0].

I would prefer *replacing* init_dummy_netdev() with
alloc_dummy_netdev(), so that we'll be sure there are no embedded
&net_devices and we can use a proper flex array there.

[0] https://elixir.bootlin.com/linux/v6.9-rc1/A/ident/init_dummy_netdev

Thanks,
Olek