Subject: Re: [RFC PATCH bridge 5/5] bridge: Add sysfs interface to display VLANS

From: Vlad Yasevich <[email-masked]>
Date: Thu, 30 Aug 2012 10:36:34 -0400

On 08/30/2012 10:26 AM, Michael S. Tsirkin wrote:
> On Thu, Aug 30, 2012 at 10:05:16AM -0400, Vlad Yasevich wrote:
>> On 08/30/2012 08:27 AM, Michael S. Tsirkin wrote:
>>> On Thu, Aug 23, 2012 at 03:29:55PM -0400, Vlad Yasevich wrote:
>>>> Add a binary sysfs file that will dump out vlans currently configured on the
>>>> port.
>>>>
>>>> Signed-off-by: Vlad Yasevich <[email-masked]>
>>>
>>> So what's the format here? I could not tell.
>>> List of vlans? Why binary? Why not make it text in that case?
>>> This would also allow reporting "all" if filtering
>>> is disabled and "untagged" for untagged packets.
>>
>> I decided to do binary because text may result in more then page
>> worth of data.
>
> Well yes, you need 3 bytes to print a vid and 1 extra for a space.

4 bytes per vid and 1 for space or NULL.

>  But
> in binary, 2 bytes per VID and there are 4K valid VIDs so binary needs
> more than 1 page too?
>
> If using binary I would go for bit per valid bit
> this solves it nicely.

True.  The tool reads it in chunks.  I thought about dumping the bitmap, 
but that meant that made the tool more complex as it had to know the 
bitmap construction.

> We can have a separate field that shows whether untagged
> packets are filtered.
>
>> The display tool will know how to display things
>> properly.
>>
>> -vlad
>
> I think you know that one of the points of sysfs
> is to allow use without tools.
> Tools are happier using other interfaces such as
> ioctl or netlink.
>

I initially though of creating a sysfs object per vlan.  That would have 
made it easy to see which vlans are configured without any tools.
But that could result in a lot of objects being created, so I abandoned it.

I did think about a text interface, but due to a page of output 
limitation, I didn't go that route.  The reason is that if someone cats 
the file, they may not see all the vlans configured.  So I decided on 
the binary interface, since a binary interface with a tool to read it 
could avoid the single page limitation.

-vlad
>
>
>>>
>>>> ---
>>>>   include/linux/if_bridge.h |    1 +
>>>>   net/bridge/br_if.c        |   34 ++++++++++++++++++++++++++++++++++
>>>>   net/bridge/br_private.h   |    2 ++
>>>>   net/bridge/br_sysfs_if.c  |   28 ++++++++++++++++++++++++++++
>>>>   4 files changed, 65 insertions(+), 0 deletions(-)
>>>>
>>>> diff --git a/include/linux/if_bridge.h b/include/linux/if_bridge.h
>>>> index ab750dd..d0f869b 100644
>>>> --- a/include/linux/if_bridge.h
>>>> +++ b/include/linux/if_bridge.h
>>>> @@ -20,6 +20,7 @@
>>>>   #define SYSFS_BRIDGE_PORT_SUBDIR "brif"
>>>>   #define SYSFS_BRIDGE_PORT_ATTR	"brport"
>>>>   #define SYSFS_BRIDGE_PORT_LINK	"bridge"
>>>> +#define SYSFS_BRIDGE_PORT_VLANS "vlans"
>>>>
>>>>   #define BRCTL_VERSION 1
>>>>
>>>> diff --git a/net/bridge/br_if.c b/net/bridge/br_if.c
>>>> index 90c1038..3963748 100644
>>>> --- a/net/bridge/br_if.c
>>>> +++ b/net/bridge/br_if.c
>>>> @@ -510,6 +510,40 @@ int br_del_port_vlan(struct net_bridge_port *p, unsigned long vlan)
>>>>   	return 0;
>>>>   }
>>>>
>>>> +size_t br_port_fill_vlans(struct net_bridge_port *p, char* buf,
>>>> +			unsigned long max, unsigned long skip)
>>>> +{
>>>> +	unsigned long *map;
>>>> +	unsigned short *vid = (unsigned short *)buf;
>>>> +	unsigned short i;
>>>> +	int num = 0;
>>>> +
>>>> +	if (skip > (VLAN_N_VID+1))
>>>> +		return -EINVAL;
>>>> +
>>>> +	memset(buf, 0, max * sizeof(unsigned short));
>>>
>>> Isn't max is in bytes? why is this safe?
>>>
>>>> +
>>>> +	rcu_read_lock();
>>>> +	map = rcu_dereference(p->vlan_map);
>>>> +	if (!map)
>>>> +		goto out;
>>>> +
>>>> +	for (i = skip + 1; i < VLAN_N_VID + 1; i++) {
>>>
>>> Isn't skip in bytes too? Why do you compare it to i which is
>>> in dwords?
>>>
>>>> +		if (test_bit(i, map)) {
>>>> +			if (num > max)
>>>> +				goto out;
>>>> +
>>>> +			*vid = i-1;
>>>> +			vid++;
>>>> +			num++;
>>>> +		}
>>>> +	}
>>>> +out:
>>>> +	rcu_read_unlock();
>>>> +
>>>> +	return num*sizeof(unsigned short);
>>>> +}
>>>> +
>>>>   void __net_exit br_net_exit(struct net *net)
>>>>   {
>>>>   	struct net_device *dev;
>>>> diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
>>>> index 5639c1c..cf95cd7 100644
>>>> --- a/net/bridge/br_private.h
>>>> +++ b/net/bridge/br_private.h
>>>> @@ -404,6 +404,8 @@ extern netdev_features_t br_features_recompute(struct net_bridge *br,
>>>>   	netdev_features_t features);
>>>>   extern int br_set_port_vlan(struct net_bridge_port *p, unsigned long vid);
>>>>   extern int br_del_port_vlan(struct net_bridge_port *p, unsigned long vid);
>>>> +extern size_t br_port_fill_vlans(struct net_bridge_port *p, char *buf,
>>>> +				unsigned long max, unsigned long skip);
>>>>
>>>>   /* br_input.c */
>>>>   extern int br_handle_frame_finish(struct sk_buff *skb);
>>>> diff --git a/net/bridge/br_sysfs_if.c b/net/bridge/br_sysfs_if.c
>>>> index 13b36bd..a81e2ef 100644
>>>> --- a/net/bridge/br_sysfs_if.c
>>>> +++ b/net/bridge/br_sysfs_if.c
>>>> @@ -234,6 +234,29 @@ const struct sysfs_ops brport_sysfs_ops = {
>>>>   };
>>>>
>>>>   /*
>>>> + * Export the vlan table for a given port as a binary file.
>>>> + * The records are unsgined shorts.
>>>> + *
>>>> + * Returns the number of bytes read.
>>>> + */
>>>> +static ssize_t brport_vlans_read(struct file *filp, struct kobject *kobj,
>>>> +				struct bin_attribute *bin_attr,
>>>> +				char *buf, loff_t off, size_t count)
>>>> +{
>>>> +	struct net_bridge_port *p = to_brport(kobj);
>>>> +
>>>> +	return br_port_fill_vlans(p, buf,
>>>> +				count/sizeof(unsigned short),
>>>> +				off/sizeof(unsigned short));
>>>> +}
>>>> +
>>>> +static struct bin_attribute port_vlans = {
>>>> +	.attr = { .name = SYSFS_BRIDGE_PORT_VLANS,
>>>> +		  .mode = S_IRUGO, },
>>>> +	.read = brport_vlans_read,
>>>> +};
>>>> +
>>>> +/*
>>>>    * Add sysfs entries to ethernet device added to a bridge.
>>>>    * Creates a brport subdirectory with bridge attributes.
>>>>    * Puts symlink in bridge's brif subdirectory
>>>> @@ -255,6 +278,11 @@ int br_sysfs_addif(struct net_bridge_port *p)
>>>>   			return err;
>>>>   	}
>>>>
>>>> +	err = sysfs_create_bin_file(&p->kobj, &port_vlans);
>>>> +	if (err) {
>>>> +		return err;
>>>> +	}
>>>> +
>>>>   	strlcpy(p->sysfs_name, p->dev->name, IFNAMSIZ);
>>>>   	return sysfs_create_link(br->ifobj, &p->kobj, p->sysfs_name);
>>>>   }
>>>> --
>>>> 1.7.7.6
>>>>
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