Regarding net_device_ops

[Pranay Srivastava]

Hi

Referring to Documentation/networking/netdevices.txt

a)

ndo->ndo_start_xmit if written "as is" will be thread safe? [Correct?]
NETIF_F_LLTX is not set only then this is true.

But dev_queue_xmit(skb) doesn't seem to take any lock, neither does
dev_hard_start_xmit. Please let me know if i'm wrong and where is this
lock taken before calling dev_queue_xmit/dev_hard_start_xmit.


b)

Why and when would I want to use rtnl_lock/unlock? Is it like
registering multiple device simultaneously?


c)

ndo->ndo_start_xmit is supposed to start the transmission of the skb.
However I've a doubt

---> Suppose that there's no room left for the incoming skb in the
device buffer, so in that case it would be ideal to call
netif_stop_queue. At this the the skb already with the ndo_start_xmit
will not be retried again[Correct?]

----> Is ndo_start_xmit required to wait in this case? However if the
above spin_lock in a) was taken then this would be a waste. So is it
possible that this skb is "deffered" to whenever there's room and
return NETDEV_TX_OK? But if we do this we are telling the application
that it's packet was delivered so in case there was a timeout set by
the application on a reply it would again send us the same packet. So
instead of "deferring" is it good to "drop" ?



-- 
        ---P.K.S