netdev - Re: [patch net-next RFC 3/3] net: export physical port id via sysfs

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Message-ID: <20130717082949.GA1582@minipsycho.orion>
Date:	Wed, 17 Jul 2013 10:29:49 +0200
From:	Jiri Pirko <jiri@...nulli.us>
To:	Narendra_K@...l.com
Cc:	netdev@...r.kernel.org, bhutchings@...arflare.com,
	john.r.fastabend@...el.com
Subject: Re: [patch net-next RFC 3/3] net: export physical port id via sysfs

Tue, Jul 16, 2013 at 10:03:04PM CEST, Narendra_K@...l.com wrote:
>> -----Original Message-----
>> From: Jiri Pirko [mailto:jiri@...nulli.us]
>> Sent: Monday, July 15, 2013 10:37 PM
>> To: netdev@...r.kernel.org
>> Cc: K, Narendra; bhutchings@...arflare.com; john.r.fastabend@...el.com
>> Subject: [patch net-next RFC 3/3] net: export physical port id via sysfs
>> 
>> Signed-off-by: Jiri Pirko <jiri@...nulli.us>
>> ---
>>  net/core/net-sysfs.c | 41
>> +++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 41 insertions(+)
>> 
>> diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c index
>> 981fed3..fb19ede 100644
>> --- a/net/core/net-sysfs.c
>> +++ b/net/core/net-sysfs.c
>> @@ -334,6 +334,46 @@ static ssize_t store_group(struct device *dev, struct
>> device_attribute *attr,
>>  	return netdev_store(dev, attr, buf, len, change_group);  }
>> 
>> +static size_t _format_port_id(char *buf, int buflen,
>> +			      const unsigned char *id, int len) {
>> +	int i;
>> +	char *cp = buf;
>> +
>> +	for (i = 0; i < len; i++)
>> +		cp += scnprintf(cp, buflen - (cp - buf), "%02x", id[i]);
>> +	return cp - buf;
>> +}
>> +
>> +ssize_t sysfs_format_port_id(char *buf, const unsigned char *id, int
>> +len) {
>> +	size_t l;
>> +
>> +	l = _format_port_id(buf, PAGE_SIZE, id, len);
>> +	l += scnprintf(buf + l, PAGE_SIZE - l, "\n");
>> +	return (ssize_t)l;
>> +}
>> +static ssize_t show_phys_port_id(struct device *dev,
>> +				 struct device_attribute *attr, char *buf) {
>> +	struct net_device *netdev = to_net_dev(dev);
>> +	ssize_t ret = 0;
>> +
>> +	if (!rtnl_trylock())
>> +		return restart_syscall();
>> +
>> +	if (dev_isalive(netdev) && netdev->netdev_ops-
>> >ndo_get_phys_port_id) {
>> +		struct netdev_phys_port_id ppid;
>> +
>> +		ret = netdev->netdev_ops->ndo_get_phys_port_id(netdev,
>> &ppid);
>[>] 
>
>Hello,
>I am thinking if "ndo_get_phys_port_id()" is required.  With it, the driver needs to generate port_id  every time "ndo_get_phys_port_id()" is called, but the "netdev->phys_port.port_id" might not have changed.  If 'phys_port'  structure is part of 'struct net_device',  then 'netdev->phys_port.port_id' and port_id_len are set by driver before calling 'register_netdev' and are available to the core.  Driver not implementing it would indicate it by a "port_id_len" of zero.     If the "netdev->phys_port.port_id" changes for some reason then the notification sent by the driver would ensure that the interested kernel components and user space are notified of the change.

Although this can be done by extending netdevice structure by another
item, I believe it is cleaner to do it by ndo. Driver has a flexibility
to either compute the phys port on fly of compute it once, store it in
it's private data and use it when ndo is called.
	
>
>With regards,
>Narendra K
>Linux Engineering
>Dell Inc.
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