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Date:   Wed, 10 Aug 2022 19:32:28 +0800
From:   "shenjian (K)" <shenjian15@...wei.com>
To:     Alexander Lobakin <alexandr.lobakin@...el.com>
CC:     <davem@...emloft.net>, <kuba@...nel.org>, <andrew@...n.ch>,
        <ecree.xilinx@...il.com>, <hkallweit1@...il.com>,
        <saeed@...nel.org>, <leon@...nel.org>, <netdev@...r.kernel.org>,
        <linuxarm@...neuler.org>
Subject: Re: [RFCv7 PATCH net-next 01/36] net: introduce operation helpers for
 netdev features



在 2022/8/10 17:43, Alexander Lobakin 写道:
> From: Jian Shen <shenjian15@...wei.com>
> Date: Wed, 10 Aug 2022 11:05:49 +0800
>
>> Introduce a set of bitmap operation helpers for netdev features,
>> then we can use them to replace the logical operation with them.
>>
>> The implementation of these helpers are based on the old prototype
>> of netdev_features_t is still u64. These helpers will be rewritten
>> on the last patch, when the prototype changes.
>>
>> To avoid interdependencies between netdev_features_helper.h and
>> netdevice.h, put the helpers for testing feature in the netdevice.h,
>> and move advandced helpers like netdev_get_wanted_features() and
>> netdev_intersect_features() to netdev_features_helper.h.
>>
>> Signed-off-by: Jian Shen <shenjian15@...wei.com>
>> ---
>>   include/linux/netdev_features.h        |  11 +
>>   include/linux/netdev_features_helper.h | 707 +++++++++++++++++++++++++
> 'netdev_feature_helpers.h' fits more I guess, doesn't it? It
> contains several helpers, not only one.
ok, will rename it.

> And BTW, do you think it's worth to create a new file rather than
> put everything just in netdev_features.h?
Jakub suggested me to move them to a new file, then it can be includued
at users appropriately. 
[https://www.spinics.net/lists/netdev/msg809370.html]

And it's unable to put everything in netdev_features.h, because these 
helpers
need to see the definition of struct net_device which is defined in 
netdevice.h.
It leading interdependence for netdeice.h include netdev_features.h.


>>   include/linux/netdevice.h              |  45 +-
>>   net/8021q/vlan_dev.c                   |   1 +
>>   net/core/dev.c                         |   1 +
>>   5 files changed, 747 insertions(+), 18 deletions(-)
>>   create mode 100644 include/linux/netdev_features_helper.h
>>
>> diff --git a/include/linux/netdev_features.h b/include/linux/netdev_features.h
>> index 7c2d77d75a88..9d434b4e6e6e 100644
>> --- a/include/linux/netdev_features.h
>> +++ b/include/linux/netdev_features.h
>> @@ -11,6 +11,17 @@
>>   
>>   typedef u64 netdev_features_t;
>>   
>> +struct netdev_feature_set {
>> +	unsigned int cnt;
>> +	unsigned short feature_bits[];
>> +};
>> +
>> +#define DECLARE_NETDEV_FEATURE_SET(name, features...)			\
>> +	const struct netdev_feature_set name = {			\
>> +		.cnt = sizeof((unsigned short[]){ features }) / sizeof(unsigned short),	\
>> +		.feature_bits = { features },				\
>> +	}
>> +
>>   enum {
>>   	NETIF_F_SG_BIT,			/* Scatter/gather IO. */
>>   	NETIF_F_IP_CSUM_BIT,		/* Can checksum TCP/UDP over IPv4. */
>> diff --git a/include/linux/netdev_features_helper.h b/include/linux/netdev_features_helper.h
>> new file mode 100644
>> index 000000000000..5423927d139b
>> --- /dev/null
>> +++ b/include/linux/netdev_features_helper.h
>> @@ -0,0 +1,707 @@
>> +/* SPDX-License-Identifier: GPL-2.0-or-later */
>> +/*
>> + * Network device features helpers.
>> + */
>> +#ifndef _LINUX_NETDEV_FEATURES_HELPER_H
>> +#define _LINUX_NETDEV_FEATURES_HELPER_H
>> +
>> +#include <linux/netdevice.h>
>> +
>> +static inline void netdev_features_zero(netdev_features_t *dst)
>> +{
>> +	*dst = 0;
>> +}
>> +
>> +/* active_feature prefer to netdev->features */
>> +#define netdev_active_features_zero(ndev) \
>> +		netdev_features_zero(&ndev->features)
> netdev_features_t sometimes is being placed and used on the stack.
> I think it's better to pass just `netdev_features_t *` to those
> helpers, this way you wouldn't also need to create a new helper
> for each net_device::*_features.
My purpose of defining  helpers for each net_device::*_features is to
avoiding driver to change  net_device::*_features directly.

>> +
>> +#define netdev_hw_features_zero(ndev) \
>> +		netdev_features_zero(&ndev->hw_features)
>> +
>> +#define netdev_wanted_features_zero(ndev) \
> [...]
>
>> +#define netdev_gso_partial_features_and(ndev, __features) \
>> +		netdev_features_and(ndev->gso_partial_features, __features)
>> +
>> +/* helpers for netdev features '&=' operation */
>> +static inline void
>> +netdev_features_mask(netdev_features_t *dst,
>> +			   const netdev_features_t features)
>> +{
>> +	*dst = netdev_features_and(*dst, features);
> A small proposal: if you look at bitmap_and() for example, it
> returns 1 if the resulting bitmap is non-empty and 0 if it is. What
> about doing the same here? It would probably help to do reduce
> boilerplating in the drivers where we only want to know if there's
> anything left after masking.
> Same for xor, toggle etc.
Thanks for point this.  Return whether empty, then I can remove 
netdev_features_intersects
helpers. But there are also many places to use 'f1 & f2' as return value 
or input param, then
I need to define more temporay features to store the result, and then 
return the temporay
features or pass into it.

>> +}
>> +
>> +static inline void
>> +netdev_active_features_mask(struct net_device *ndev,
>> +			    const netdev_features_t features)
>> +{
>> +	ndev->features = netdev_active_features_and(ndev, features);
>> +}
> [...]
>
>> +/* helpers for netdev features 'set bit array' operation */
>> +static inline void
>> +netdev_features_set_array(const struct netdev_feature_set *set,
>> +			  netdev_features_t *dst)
>> +{
>> +	int i;
>> +
>> +	for (i = 0; i < set->cnt; i++)
> Nit: kernel is C11 now, you can do just `for (u32 i = 0; i ...`.
> (and yeah, it's better to use unsigned types when you don't plan
> to store negative values there).
ok, will fix it.

>> +		netdev_feature_add(set->feature_bits[i], dst);
>> +}
> [...]
>
>> -- 
>> 2.33.0
> Thanks,
> Olek
>
> .
>

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