Date:   Fri, 12 Aug 2022 10:39:17 +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 2022/8/11 18:49, Alexander Lobakin 写道:
> From: "shenjian (K)" <shenjian15@...wei.com>
> Date: Wed, 10 Aug 2022 19:32:28 +0800
>
>> 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.
>
> Ah, correct then, sure! I missed that fact.
>
>>
>>
>> >>   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.
>
> But why? My point is that you have to create a whole bunch of
> copy'n'paste functions differing only by the &net_device field
> name.
>
I noticed that Jakub have done a lot work for avoiding driver to write 
netdev->dev_addr
directly. Also in earlier discuss, Saeed had suggested to hide hide the 
implementation
details and abstract it away from drivers using getters and manipulation 
APIs.
[https://lore.kernel.org/all/b335852ecaba3c86d1745b5021bb500798fc843b.camel@kernel.org/]


>>
>> >> +
>> >> +#define netdev_hw_features_zero(ndev) \
>> >> + netdev_features_zero(&ndev->hw_features)
>
> Oh BTW: wrap `ndev` in the netdev_features_zero() call into braces,
> `netdev_feature_zero(&(ndev)->hw_features)`, otherwise it may cause
> unwanted sneaky logical changes or build failures.
>
OK, will fix it.

>> >> +
>> >> +#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.
>
> No, netdev_features_intersects() is okay, leave it as it is. Just
> look on bitmap_*() prototypes and return its values when applicable.
>
OK, will follow the prototypes of bitmap_and and others.


>>
>> >> +}
>> >> +
>> >> +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
>> >
>> > .
>
> Thanks,
> Olek
>
> .
>
Thanks,
Jian

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