centos man page for dev_queue_xmit

DEV_QUEUE_XMIT(9)					      Network device support						 DEV_QUEUE_XMIT(9)

NAME
       dev_queue_xmit - transmit a buffer

SYNOPSIS
       int dev_queue_xmit(struct sk_buff * skb);

ARGUMENTS
       skb
	   buffer to transmit

DESCRIPTION
       Queue a buffer for transmission to a network device. The caller must have set the device and priority and built the buffer before calling
       this function. The function can be called from an interrupt.

       A negative errno code is returned on a failure. A success does not guarantee the frame will be transmitted as it may be dropped due to
       congestion or traffic shaping.

       ----------------------------------------------------------------------------------- I notice this method can also return errors from the
       queue disciplines, including NET_XMIT_DROP, which is a positive value. So, errors can also be positive.

       Regardless of the return value, the skb is consumed, so it is currently difficult to retry a send to this method. (You can bump the ref
       count before sending to hold a reference for retry if you are careful.)

       When calling this method, interrupts MUST be enabled. This is because the BH enable code must have IRQs enabled so that it will not
       deadlock. --BLG

COPYRIGHT
Kernel Hackers Manual 3.10					     June 2014							 DEV_QUEUE_XMIT(9)