Re: [RFC PATCH net-next 2/4] switchdev: add fwd_mark generator helper

Sergei Shtylyov
2015-06-15T14:09:18Z

Hello.

On 6/15/2015 4:52 PM, Scott Feldman wrote:

>>>>> From: Scott Feldman <sfeldma@gmail.com>

>>>>> skb->fwd_mark and dev->fwd_mark are 32-bit and should be unique for device
>>>>> and maybe even unique for a sub-set of ports within device, so add
>>>>> switchdev helper function to generate unique marks based on driver-supplied
>>>>> key. Typically, the driver would use device switch ID for key, and maybe
>>>>> additional fields in key for grouped ports such as bridge ifindex. The key
>>>>> can be of arbitrary length.

>>>>> The generator uses a global hash table to store fwd_marks hashed by key.

>>>>> Signed-off-by: Scott Feldman <sfeldma@gmail.com>

>>> <snip>

>>>>> +u32 switchdev_mark_get(void *key, size_t key_len)
>>>>> +{
>>>>> + struct switchdev_mark_ht_entry {
>>>>> + struct hlist_node entry;
>>>>> + void *key;
>>>>> + size_t key_len;
>>>>> + u32 key_crc32;
>>>>> + u32 mark;
>>>>> + } *entry;
>>>>> + u32 key_crc32 = crc32(~0, key, key_len);
>>>>> + u32 mark = 0;
>>>>> + unsigned long flags;
>>>>> +
>>>>> + spin_lock_irqsave(&switchdev_mark_lock, flags);

>>>> I fail to see why _irqsave variant is needed here.

>>> I don't know what context caller is in, so using most conservative
>>> spinlock. Is there a better way?

>> I don't see why would someone call this from irq.

> Ok, good point, I'll adjust to spin_lock.

I guess spi_lock_irq() is what you meant. Disabling IRQs when called from
the hardirq context made no sense since hardirq handlrs are executed with IRQs
disabled anyway.

WBR, Sergei