Date:   Mon, 11 Apr 2022 15:39:20 -0700
From:   Vinicius Costa Gomes <vinicius.gomes@...el.com>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "jhs@...atatu.com" <jhs@...atatu.com>,
        "xiyou.wangcong@...il.com" <xiyou.wangcong@...il.com>,
        "jiri@...nulli.us" <jiri@...nulli.us>,
        "kuba@...nel.org" <kuba@...nel.org>, Po Liu <po.liu@....com>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
        "anthony.l.nguyen@...el.com" <anthony.l.nguyen@...el.com>,
        "mkubecek@...e.cz" <mkubecek@...e.cz>
Subject: Re: [PATCH net-next v4 01/12] ethtool: Add support for configuring
 frame preemption

Hi,

(bringing an old thread back to life)

Vladimir Oltean <vladimir.oltean@....com> writes:

> On Fri, Jun 25, 2021 at 05:33:03PM -0700, Vinicius Costa Gomes wrote:
>> Frame preemption (described in IEEE 802.3-2018, Section 99 in
>> particular) defines the concept of preemptible and express queues. It
>> allows traffic from express queues to "interrupt" traffic from
>> preemptible queues, which are "resumed" after the express traffic has
>> finished transmitting.
>> 
>> Frame preemption can only be used when both the local device and the
>> link partner support it.
>> 
>> Only parameters for enabling/disabling frame preemption and
>> configuring the minimum fragment size are included here. Expressing
>> which queues are marked as preemptible is left to mqprio/taprio, as
>> having that information there should be easier on the user.
>> 
>> Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@...el.com>
>> ---
>>  Documentation/networking/ethtool-netlink.rst |  38 +++++
>>  include/linux/ethtool.h                      |  22 +++
>>  include/uapi/linux/ethtool_netlink.h         |  17 +++
>>  net/ethtool/Makefile                         |   2 +-
>>  net/ethtool/common.c                         |  25 ++++
>>  net/ethtool/netlink.c                        |  19 +++
>>  net/ethtool/netlink.h                        |   4 +
>>  net/ethtool/preempt.c                        | 146 +++++++++++++++++++
>>  8 files changed, 272 insertions(+), 1 deletion(-)
>>  create mode 100644 net/ethtool/preempt.c
>> 
>> diff --git a/Documentation/networking/ethtool-netlink.rst b/Documentation/networking/ethtool-netlink.rst
>> index 6ea91e41593f..a87f1716944e 100644
>> --- a/Documentation/networking/ethtool-netlink.rst
>> +++ b/Documentation/networking/ethtool-netlink.rst
>> @@ -1477,6 +1477,44 @@ Low and high bounds are inclusive, for example:
>>   etherStatsPkts512to1023Octets 512  1023
>>   ============================= ==== ====
>
> I think you need to add some extra documentation bits to the
>
> List of message types
> =====================
>
> and
>
> Request translation
> ===================
>
> sections.
>

Will add some more documentation.

>>  
>> +PREEMPT_GET
>> +===========
>> +
>> +Get information about frame preemption state.
>> +
>> +Request contents:
>> +
>> +  ====================================  ======  ==========================
>> +  ``ETHTOOL_A_PREEMPT_HEADER``          nested  request header
>> +  ====================================  ======  ==========================
>> +
>> +Request contents:
>> +
>> +  =====================================  ======  ==========================
>> +  ``ETHTOOL_A_PREEMPT_HEADER``           nested  reply header
>> +  ``ETHTOOL_A_PREEMPT_ENABLED``          u8      frame preemption enabled
>> +  ``ETHTOOL_A_PREEMPT_ADD_FRAG_SIZE``    u32     Min additional frag size
>> +  =====================================  ======  ==========================
>> +
>> +``ETHTOOL_A_PREEMPT_ADD_FRAG_SIZE`` configures the minimum non-final
>> +fragment size that the receiver device supports.
>> +
>> +PREEMPT_SET
>> +===========
>> +
>> +Sets frame preemption parameters.
>> +
>> +Request contents:
>> +
>> +  =====================================  ======  ==========================
>> +  ``ETHTOOL_A_CHANNELS_HEADER``          nested  reply header
>> +  ``ETHTOOL_A_PREEMPT_ENABLED``          u8      frame preemption enabled
>> +  ``ETHTOOL_A_PREEMPT_ADD_FRAG_SIZE``    u32     Min additional frag size
>> +  =====================================  ======  ==========================
>> +
>> +``ETHTOOL_A_PREEMPT_ADD_FRAG_SIZE`` configures the minimum non-final
>> +fragment size that the receiver device supports.
>> +
>>  Request translation
>>  ===================
>>  
>> diff --git a/include/linux/ethtool.h b/include/linux/ethtool.h
>> index 29dbb603bc91..7e449be8f335 100644
>> --- a/include/linux/ethtool.h
>> +++ b/include/linux/ethtool.h
>> @@ -409,6 +409,19 @@ struct ethtool_module_eeprom {
>>  	u8	*data;
>>  };
>>  
>> +/**
>> + * struct ethtool_fp - Frame Preemption information
>> + *
>> + * @enabled: Enable frame preemption.
>> + * @add_frag_size: Minimum size for additional (non-final) fragments
>> + * in bytes, for the value defined in the IEEE 802.3-2018 standard see
>> + * ethtool_frag_size_to_mult().
>> + */
>> +struct ethtool_fp {
>> +	u8 enabled;
>> +	u32 add_frag_size;
>
> Strange that the verify_disable bit is not in here? I haven't looked at
> further patches in detail but I saw in the commit message that you added
> support for it, maybe it needs to be squashed with this?

Will squash the commit that exposes verification config via netlink into this.

>
> Can we make "enabled" a bool?

It seems that the current convention is to use u32 to represent booleans
in the ethtool/netlink API. See ethnl_update_bool32(), will use this instead.

>
>> +};
>> +
>>  /**
>>   * struct ethtool_ops - optional netdev operations
>>   * @cap_link_lanes_supported: indicates if the driver supports lanes
>> @@ -561,6 +574,8 @@ struct ethtool_module_eeprom {
>>   *	not report statistics.
>>   * @get_fecparam: Get the network device Forward Error Correction parameters.
>>   * @set_fecparam: Set the network device Forward Error Correction parameters.
>> + * @get_preempt: Get the network device Frame Preemption parameters.
>> + * @set_preempt: Set the network device Frame Preemption parameters.
>>   * @get_ethtool_phy_stats: Return extended statistics about the PHY device.
>>   *	This is only useful if the device maintains PHY statistics and
>>   *	cannot use the standard PHY library helpers.
>> @@ -675,6 +690,10 @@ struct ethtool_ops {
>>  				      struct ethtool_fecparam *);
>>  	int	(*set_fecparam)(struct net_device *,
>>  				      struct ethtool_fecparam *);
>> +	int	(*get_preempt)(struct net_device *,
>> +			       struct ethtool_fp *);
>> +	int	(*set_preempt)(struct net_device *, struct ethtool_fp *,
>> +			       struct netlink_ext_ack *);
>>  	void	(*get_ethtool_phy_stats)(struct net_device *,
>>  					 struct ethtool_stats *, u64 *);
>>  	int	(*get_phy_tunable)(struct net_device *,
>> @@ -766,4 +785,7 @@ ethtool_params_from_link_mode(struct ethtool_link_ksettings *link_ksettings,
>>   * next string.
>>   */
>>  extern __printf(2, 3) void ethtool_sprintf(u8 **data, const char *fmt, ...);
>> +
>> +u8 ethtool_frag_size_to_mult(u32 frag_size);
>> +
>>  #endif /* _LINUX_ETHTOOL_H */
>> diff --git a/include/uapi/linux/ethtool_netlink.h b/include/uapi/linux/ethtool_netlink.h
>> index c7135c9c37a5..4600aba1c693 100644
>> --- a/include/uapi/linux/ethtool_netlink.h
>> +++ b/include/uapi/linux/ethtool_netlink.h
>> @@ -44,6 +44,8 @@ enum {
>>  	ETHTOOL_MSG_TUNNEL_INFO_GET,
>>  	ETHTOOL_MSG_FEC_GET,
>>  	ETHTOOL_MSG_FEC_SET,
>> +	ETHTOOL_MSG_PREEMPT_GET,
>> +	ETHTOOL_MSG_PREEMPT_SET,
>>  	ETHTOOL_MSG_MODULE_EEPROM_GET,
>>  	ETHTOOL_MSG_STATS_GET,
>>  
>> @@ -86,6 +88,8 @@ enum {
>>  	ETHTOOL_MSG_TUNNEL_INFO_GET_REPLY,
>>  	ETHTOOL_MSG_FEC_GET_REPLY,
>>  	ETHTOOL_MSG_FEC_NTF,
>> +	ETHTOOL_MSG_PREEMPT_GET_REPLY,
>> +	ETHTOOL_MSG_PREEMPT_NTF,
>>  	ETHTOOL_MSG_MODULE_EEPROM_GET_REPLY,
>>  	ETHTOOL_MSG_STATS_GET_REPLY,
>
> Correct me if I'm wrong, but enums in uapi should always be added at the
> end, otherwise you break value with user space binaries which use
> ETHTOOL_MSG_MODULE_EEPROM_GET and are compiled against old kernel
> headers.

Fixed.

>
>>  
>> @@ -664,6 +668,19 @@ enum {
>>  	ETHTOOL_A_FEC_STAT_MAX = (__ETHTOOL_A_FEC_STAT_CNT - 1)
>>  };
>>  
>> +/* FRAME PREEMPTION */
>> +
>> +enum {
>> +	ETHTOOL_A_PREEMPT_UNSPEC,
>> +	ETHTOOL_A_PREEMPT_HEADER,			/* nest - _A_HEADER_* */
>> +	ETHTOOL_A_PREEMPT_ENABLED,			/* u8 */
>> +	ETHTOOL_A_PREEMPT_ADD_FRAG_SIZE,		/* u32 */
>> +
>> +	/* add new constants above here */
>> +	__ETHTOOL_A_PREEMPT_CNT,
>> +	ETHTOOL_A_PREEMPT_MAX = (__ETHTOOL_A_PREEMPT_CNT - 1)
>> +};
>> +
>>  /* MODULE EEPROM */
>>  
>>  enum {
>> diff --git a/net/ethtool/Makefile b/net/ethtool/Makefile
>> index 723c9a8a8cdf..4b84b2d34c7a 100644
>> --- a/net/ethtool/Makefile
>> +++ b/net/ethtool/Makefile
>> @@ -7,4 +7,4 @@ obj-$(CONFIG_ETHTOOL_NETLINK)	+= ethtool_nl.o
>>  ethtool_nl-y	:= netlink.o bitset.o strset.o linkinfo.o linkmodes.o \
>>  		   linkstate.o debug.o wol.o features.o privflags.o rings.o \
>>  		   channels.o coalesce.o pause.o eee.o tsinfo.o cabletest.o \
>> -		   tunnels.o fec.o eeprom.o stats.o
>> +		   tunnels.o fec.o preempt.o eeprom.o stats.o
>> diff --git a/net/ethtool/common.c b/net/ethtool/common.c
>> index f9dcbad84788..68d123dd500b 100644
>> --- a/net/ethtool/common.c
>> +++ b/net/ethtool/common.c
>> @@ -579,3 +579,28 @@ ethtool_params_from_link_mode(struct ethtool_link_ksettings *link_ksettings,
>>  	link_ksettings->base.duplex = link_info->duplex;
>>  }
>>  EXPORT_SYMBOL_GPL(ethtool_params_from_link_mode);
>> +
>> +/**
>> + * ethtool_frag_size_to_mult() - Convert from a Frame Preemption
>> + * Additional Fragment size in bytes to a multiplier.
>> + * @frag_size: minimum non-final fragment size in bytes.
>> + *
>> + * The multiplier is defined as:
>> + *	"A 2-bit integer value used to indicate the minimum size of
>> + *	non-final fragments supported by the receiver on the given port
>> + *	associated with the local System. This value is expressed in units
>> + *	of 64 octets of additional fragment length."
>> + *	Equivalent to `30.14.1.7 aMACMergeAddFragSize` from the IEEE 802.3-2018
>> + *	standard.
>> + *
>> + * Return: the multiplier is a number in the [0, 2] interval.
>> + */
>> +u8 ethtool_frag_size_to_mult(u32 frag_size)
>> +{
>> +	u8 mult = (frag_size / 64) - 1;
>> +
>> +	mult = clamp_t(u8, mult, 0, 3);
>> +
>> +	return mult;
>
> I think it would look better as "return clamp_t(u8, mult, 0, 3);"

Fixed.

>
>> +}
>> +EXPORT_SYMBOL_GPL(ethtool_frag_size_to_mult);
>> diff --git a/net/ethtool/netlink.c b/net/ethtool/netlink.c
>> index a7346346114f..f4e07b740790 100644
>> --- a/net/ethtool/netlink.c
>> +++ b/net/ethtool/netlink.c
>> @@ -246,6 +246,7 @@ ethnl_default_requests[__ETHTOOL_MSG_USER_CNT] = {
>>  	[ETHTOOL_MSG_EEE_GET]		= &ethnl_eee_request_ops,
>>  	[ETHTOOL_MSG_FEC_GET]		= &ethnl_fec_request_ops,
>>  	[ETHTOOL_MSG_TSINFO_GET]	= &ethnl_tsinfo_request_ops,
>> +	[ETHTOOL_MSG_PREEMPT_GET]	= &ethnl_preempt_request_ops,
>>  	[ETHTOOL_MSG_MODULE_EEPROM_GET]	= &ethnl_module_eeprom_request_ops,
>>  	[ETHTOOL_MSG_STATS_GET]		= &ethnl_stats_request_ops,
>>  };
>> @@ -561,6 +562,7 @@ ethnl_default_notify_ops[ETHTOOL_MSG_KERNEL_MAX + 1] = {
>>  	[ETHTOOL_MSG_PAUSE_NTF]		= &ethnl_pause_request_ops,
>>  	[ETHTOOL_MSG_EEE_NTF]		= &ethnl_eee_request_ops,
>>  	[ETHTOOL_MSG_FEC_NTF]		= &ethnl_fec_request_ops,
>> +	[ETHTOOL_MSG_PREEMPT_NTF]	= &ethnl_preempt_request_ops,
>>  };
>>  
>>  /* default notification handler */
>> @@ -654,6 +656,7 @@ static const ethnl_notify_handler_t ethnl_notify_handlers[] = {
>>  	[ETHTOOL_MSG_PAUSE_NTF]		= ethnl_default_notify,
>>  	[ETHTOOL_MSG_EEE_NTF]		= ethnl_default_notify,
>>  	[ETHTOOL_MSG_FEC_NTF]		= ethnl_default_notify,
>> +	[ETHTOOL_MSG_PREEMPT_NTF]	= ethnl_default_notify,
>>  };
>>  
>>  void ethtool_notify(struct net_device *dev, unsigned int cmd, const void *data)
>> @@ -958,6 +961,22 @@ static const struct genl_ops ethtool_genl_ops[] = {
>>  		.policy = ethnl_stats_get_policy,
>>  		.maxattr = ARRAY_SIZE(ethnl_stats_get_policy) - 1,
>>  	},
>> +	{
>> +		.cmd	= ETHTOOL_MSG_PREEMPT_GET,
>> +		.doit	= ethnl_default_doit,
>> +		.start	= ethnl_default_start,
>> +		.dumpit	= ethnl_default_dumpit,
>> +		.done	= ethnl_default_done,
>> +		.policy = ethnl_preempt_get_policy,
>> +		.maxattr = ARRAY_SIZE(ethnl_preempt_get_policy) - 1,
>> +	},
>> +	{
>> +		.cmd	= ETHTOOL_MSG_PREEMPT_SET,
>> +		.flags	= GENL_UNS_ADMIN_PERM,
>> +		.doit	= ethnl_set_preempt,
>> +		.policy = ethnl_preempt_set_policy,
>> +		.maxattr = ARRAY_SIZE(ethnl_preempt_set_policy) - 1,
>> +	},
>>  };
>>  
>>  static const struct genl_multicast_group ethtool_nl_mcgrps[] = {
>> diff --git a/net/ethtool/netlink.h b/net/ethtool/netlink.h
>> index 3e25a47fd482..cc90a463a81c 100644
>> --- a/net/ethtool/netlink.h
>> +++ b/net/ethtool/netlink.h
>> @@ -345,6 +345,7 @@ extern const struct ethnl_request_ops ethnl_pause_request_ops;
>>  extern const struct ethnl_request_ops ethnl_eee_request_ops;
>>  extern const struct ethnl_request_ops ethnl_tsinfo_request_ops;
>>  extern const struct ethnl_request_ops ethnl_fec_request_ops;
>> +extern const struct ethnl_request_ops ethnl_preempt_request_ops;
>>  extern const struct ethnl_request_ops ethnl_module_eeprom_request_ops;
>>  extern const struct ethnl_request_ops ethnl_stats_request_ops;
>>  
>> @@ -381,6 +382,8 @@ extern const struct nla_policy ethnl_tunnel_info_get_policy[ETHTOOL_A_TUNNEL_INF
>>  extern const struct nla_policy ethnl_fec_get_policy[ETHTOOL_A_FEC_HEADER + 1];
>>  extern const struct nla_policy ethnl_fec_set_policy[ETHTOOL_A_FEC_AUTO + 1];
>>  extern const struct nla_policy ethnl_module_eeprom_get_policy[ETHTOOL_A_MODULE_EEPROM_I2C_ADDRESS + 1];
>> +extern const struct nla_policy ethnl_preempt_get_policy[ETHTOOL_A_PREEMPT_HEADER + 1];
>> +extern const struct nla_policy ethnl_preempt_set_policy[ETHTOOL_A_PREEMPT_ADD_FRAG_SIZE + 1];
>>  extern const struct nla_policy ethnl_stats_get_policy[ETHTOOL_A_STATS_GROUPS + 1];
>>  
>>  int ethnl_set_linkinfo(struct sk_buff *skb, struct genl_info *info);
>> @@ -400,6 +403,7 @@ int ethnl_tunnel_info_doit(struct sk_buff *skb, struct genl_info *info);
>>  int ethnl_tunnel_info_start(struct netlink_callback *cb);
>>  int ethnl_tunnel_info_dumpit(struct sk_buff *skb, struct netlink_callback *cb);
>>  int ethnl_set_fec(struct sk_buff *skb, struct genl_info *info);
>> +int ethnl_set_preempt(struct sk_buff *skb, struct genl_info *info);
>>  
>>  extern const char stats_std_names[__ETHTOOL_STATS_CNT][ETH_GSTRING_LEN];
>>  extern const char stats_eth_phy_names[__ETHTOOL_A_STATS_ETH_PHY_CNT][ETH_GSTRING_LEN];
>> diff --git a/net/ethtool/preempt.c b/net/ethtool/preempt.c
>> new file mode 100644
>> index 000000000000..4f96d3c2b1d5
>> --- /dev/null
>> +++ b/net/ethtool/preempt.c
>> @@ -0,0 +1,146 @@
>> +// SPDX-License-Identifier: GPL-2.0-only
>> +
>> +#include "netlink.h"
>> +#include "common.h"
>> +
>> +struct preempt_req_info {
>> +	struct ethnl_req_info		base;
>> +};
>> +
>> +struct preempt_reply_data {
>> +	struct ethnl_reply_data		base;
>> +	struct ethtool_fp		fp;
>> +};
>> +
>> +#define PREEMPT_REPDATA(__reply_base) \
>> +	container_of(__reply_base, struct preempt_reply_data, base)
>> +
>> +const struct nla_policy
>> +ethnl_preempt_get_policy[] = {
>> +	[ETHTOOL_A_PREEMPT_HEADER]		= NLA_POLICY_NESTED(ethnl_header_policy),
>> +};
>> +
>> +static int preempt_prepare_data(const struct ethnl_req_info *req_base,
>> +				struct ethnl_reply_data *reply_base,
>> +				struct genl_info *info)
>> +{
>> +	struct preempt_reply_data *data = PREEMPT_REPDATA(reply_base);
>> +	struct net_device *dev = reply_base->dev;
>> +	int ret;
>> +
>> +	if (!dev->ethtool_ops->get_preempt)
>> +		return -EOPNOTSUPP;
>> +
>> +	ret = ethnl_ops_begin(dev);
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	ret = dev->ethtool_ops->get_preempt(dev, &data->fp);
>> +	ethnl_ops_complete(dev);
>> +
>> +	return ret;
>> +}
>> +
>> +static int preempt_reply_size(const struct ethnl_req_info *req_base,
>> +			      const struct ethnl_reply_data *reply_base)
>> +{
>> +	int len = 0;
>> +
>> +	len += nla_total_size(sizeof(u8)); /* _PREEMPT_ENABLED */
>> +	len += nla_total_size(sizeof(u32)); /* _PREEMPT_ADD_FRAG_SIZE */
>> +
>> +	return len;
>> +}
>> +
>> +static int preempt_fill_reply(struct sk_buff *skb,
>> +			      const struct ethnl_req_info *req_base,
>> +			      const struct ethnl_reply_data *reply_base)
>> +{
>> +	const struct preempt_reply_data *data = PREEMPT_REPDATA(reply_base);
>> +	const struct ethtool_fp *preempt = &data->fp;
>> +
>> +	if (nla_put_u8(skb, ETHTOOL_A_PREEMPT_ENABLED, preempt->enabled))
>> +		return -EMSGSIZE;
>> +
>> +	if (nla_put_u32(skb, ETHTOOL_A_PREEMPT_ADD_FRAG_SIZE,
>> +			preempt->add_frag_size))
>> +		return -EMSGSIZE;
>> +
>> +	return 0;
>> +}
>> +
>> +const struct ethnl_request_ops ethnl_preempt_request_ops = {
>> +	.request_cmd		= ETHTOOL_MSG_PREEMPT_GET,
>> +	.reply_cmd		= ETHTOOL_MSG_PREEMPT_GET_REPLY,
>> +	.hdr_attr		= ETHTOOL_A_PREEMPT_HEADER,
>> +	.req_info_size		= sizeof(struct preempt_req_info),
>> +	.reply_data_size	= sizeof(struct preempt_reply_data),
>> +
>> +	.prepare_data		= preempt_prepare_data,
>> +	.reply_size		= preempt_reply_size,
>> +	.fill_reply		= preempt_fill_reply,
>> +};
>> +
>> +const struct nla_policy
>> +ethnl_preempt_set_policy[ETHTOOL_A_PREEMPT_MAX + 1] = {
>> +	[ETHTOOL_A_PREEMPT_HEADER]			= NLA_POLICY_NESTED(ethnl_header_policy),
>> +	[ETHTOOL_A_PREEMPT_ENABLED]			= NLA_POLICY_RANGE(NLA_U8, 0, 1),
>> +	[ETHTOOL_A_PREEMPT_ADD_FRAG_SIZE]		= { .type = NLA_U32 },
>> +};
>> +
>> +int ethnl_set_preempt(struct sk_buff *skb, struct genl_info *info)
>> +{
>> +	struct ethnl_req_info req_info = {};
>> +	struct nlattr **tb = info->attrs;
>> +	struct ethtool_fp preempt = {};
>> +	struct net_device *dev;
>> +	bool mod = false;
>> +	int ret;
>> +
>> +	ret = ethnl_parse_header_dev_get(&req_info,
>> +					 tb[ETHTOOL_A_PREEMPT_HEADER],
>> +					 genl_info_net(info), info->extack,
>> +					 true);
>> +	if (ret < 0)
>> +		return ret;
>> +	dev = req_info.dev;
>> +	ret = -EOPNOTSUPP;
>
> Some new lines around here please? And maybe it would look a bit cleaner
> if you could assign "ret = -EOPNOTSUPP" in the "preempt ops not present"
> if condition body?
>

I will add more vertical spaces. About the error returning idioms, even
if they are not my preferred style, they are consistent with the other
files in net/ethtool, so will keep that as it is.

>> +	if (!dev->ethtool_ops->get_preempt ||
>> +	    !dev->ethtool_ops->set_preempt)
>> +		goto out_dev;
>> +
>> +	rtnl_lock();
>> +	ret = ethnl_ops_begin(dev);
>> +	if (ret < 0)
>> +		goto out_rtnl;
>> +
>> +	ret = dev->ethtool_ops->get_preempt(dev, &preempt);
>
> I don't know much about the background of ethtool netlink, but why does
> the .doit of ETHTOOL_MSG_*_SET go through a getter first? Is it because
> all the netlink attributes from the message are optional, and we need to
> default to the current state?
>

Yes, and there's the "optimization" that the setter will only be called
if there's any modification, so we need to know the current state.

>> +	if (ret < 0) {
>> +		GENL_SET_ERR_MSG(info, "failed to retrieve frame preemption settings");
>> +		goto out_ops;
>> +	}
>> +
>> +	ethnl_update_u8(&preempt.enabled,
>> +			tb[ETHTOOL_A_PREEMPT_ENABLED], &mod);
>> +	ethnl_update_u32(&preempt.add_frag_size,
>> +			 tb[ETHTOOL_A_PREEMPT_ADD_FRAG_SIZE], &mod);
>> +	ret = 0;
>
> This reinitialization of ret to zero is interesting. It implies
> ->get_preempt() is allowed to return > 0 as a success error code.
> However ->set_preempt() below isn't? (its return value is directly
> propagated to callers of ethnl_set_preempt().
>

It also applies to other "commands" in net/ethtool. My feeling is that
this is more like a undocumented convention than a bug (following what
the first command did). Will leave as it is, unless there are strong
feelings.


>> +	if (!mod)
>> +		goto out_ops;
>> +
>> +	ret = dev->ethtool_ops->set_preempt(dev, &preempt, info->extack);
>> +	if (ret < 0) {
>> +		GENL_SET_ERR_MSG(info, "frame preemption settings update failed");
>> +		goto out_ops;
>> +	}
>> +
>> +	ethtool_notify(dev, ETHTOOL_MSG_PREEMPT_NTF, NULL);
>> +
>> +out_ops:
>> +	ethnl_ops_complete(dev);
>> +out_rtnl:
>> +	rtnl_unlock();
>> +out_dev:
>> +	dev_put(dev);
>> +	return ret;
>> +}
>> -- 
>> 2.32.0
>> 


Cheers,
-- 
Vinicius

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