Subject: Re: [RFC 1/2] net: Support getting/setting RX-FCS in drivers.

From: Ben Greear <[email-masked]>
Date: Fri, 17 Jun 2011 08:33:06 -0700

On 06/17/2011 05:20 AM, Ben Hutchings wrote:
> On Thu, 2011-06-16 at 21:30 -0700, [email-masked] wrote:
>> From: Ben Greear<[email-masked]>
>>
>> This will allow us to enable/disable having the Ethernet
>> frame checksum appended to the skb.  Enabling this is
>> useful when sniffing packets.
>>
>> In particular, this can be used to test logic that allows
>> a NIC to receive all frames, even ones with bad checksums.
>>
>> Signed-off-by: Ben Greear<[email-masked]>
>> ---
>> :100644 100644 439b173... e5e8747... M	include/linux/ethtool.h
>> :100644 100644 fd14116... b36bac7... M	net/core/ethtool.c
>>   include/linux/ethtool.h |    5 +++++
>>   net/core/ethtool.c      |   38 ++++++++++++++++++++++++++++++++++++++
>>   2 files changed, 43 insertions(+), 0 deletions(-)
>>
>> diff --git a/include/linux/ethtool.h b/include/linux/ethtool.h
>> index 439b173..e5e8747 100644
>> --- a/include/linux/ethtool.h
>> +++ b/include/linux/ethtool.h
>> @@ -955,6 +955,8 @@ struct ethtool_ops {
>>   	int	(*get_dump_data)(struct net_device *,
>>   				 struct ethtool_dump *, void *);
>>   	int	(*set_dump)(struct net_device *, struct ethtool_dump *);
>> +	int	(*set_save_fcs)(struct net_device *, u32);
>> +	int	(*get_save_fcs)(struct net_device *, u32 *);
>
> These need to be described in the kernel-doc.
>
> Why do these function names use 'save_fcs' whereas the command names use
> 'RXFCS'?
>
>>   };
>>   #endif /* __KERNEL__ */
>> @@ -1029,6 +1031,9 @@ struct ethtool_ops {
>>   #define ETHTOOL_SET_DUMP	0x0000003e /* Set dump settings */
>>   #define ETHTOOL_GET_DUMP_FLAG	0x0000003f /* Get dump settings */
>>   #define ETHTOOL_GET_DUMP_DATA	0x00000040 /* Get dump data */
>> +#define ETHTOOL_GETRXFCS	0x00000041 /* Get RX Save Frame Checksum */
>> +#define ETHTOOL_SETRXFCS	0x00000042 /* Set RX Save Frame Checksum */
>> +
>>
>>   /* compatibility with older code */
>>   #define SPARC_ETH_GSET		ETHTOOL_GSET
>> diff --git a/net/core/ethtool.c b/net/core/ethtool.c
>> index fd14116..b36bac7 100644
>> --- a/net/core/ethtool.c
>> +++ b/net/core/ethtool.c
>> @@ -1927,6 +1927,38 @@ out:
>>   	return ret;
>>   }
>>
>> +static int ethtool_get_rx_fcs(struct net_device *dev, void __user *useraddr)
>> +{
>> +	struct ethtool_value edata;
>> +	int rv = 0;
>> +
>> +	if (!dev->ethtool_ops->get_save_fcs)
>> +		return -EOPNOTSUPP;
>> +
>> +	rv = dev->ethtool_ops->get_save_fcs(dev,&edata.data);
>> +	if (rv<  0)
>> +		return rv;
>> +
>> +	if (copy_to_user(useraddr,&edata, sizeof(edata)))
>> +		return -EFAULT;
>> +	return 0;
>> +}
>> +
>> +
>> +static int ethtool_set_rx_fcs(struct net_device *dev, void __user *useraddr)
>> +{
>> +	struct ethtool_value id;
>> +
>> +	if (!dev->ethtool_ops->set_save_fcs)
>> +		return -EOPNOTSUPP;
>> +
>> +	if (copy_from_user(&id, useraddr, sizeof(id)))
>> +		return -EFAULT;
>> +
>> +	return dev->ethtool_ops->set_save_fcs(dev, id.data);
>> +}
>> +
>> +
>>   /* The main entry point in this file.  Called from net/core/dev.c */
>>
>>   int dev_ethtool(struct net *net, struct ifreq *ifr)
>> @@ -2152,6 +2184,12 @@ int dev_ethtool(struct net *net, struct ifreq *ifr)
>>   	case ETHTOOL_GET_DUMP_DATA:
>>   		rc = ethtool_get_dump_data(dev, useraddr);
>>   		break;
>> +	case ETHTOOL_SETRXFCS:
>> +		rc = ethtool_set_rx_fcs(dev, useraddr);
>> +		break;
>> +	case ETHTOOL_GETRXFCS:
>> +		rc = ethtool_get_rx_fcs(dev, useraddr);
>> +		break;
>
> You can use ethtool_{get,set}_value() rather than adding new trivial
> functions.

I'll look at that.

>
> And as Michal says, this could reasonably be a feature not an entirely
> separate flag.  I'm not sure it's that important to have debugging flags
> in features, but I also don't want to have 2 commands per flag...

I'm not sure it really counts as a feature, and I've no desire to tangle
with the effort to extend features beyond 32 bits.  Maybe we could have a new
ethtool command that took a struct with two args, so we can "set flag-foo val"
instead of 'enable-flag-foo' and 'disable-flag-foo'?

That should be only one additional method for the drivers to implement, and
can be used for the other patches I have planned as well.

Thanks,
Ben

-- 
Ben Greear <[email-masked]>
Candela Technologies Inc  http://www.candelatech.com