From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Miller <davem@davemloft.net>
Subject: Re: network devices don't handle pci_dma_mapping_error()'s
Date: Wed, 06 Dec 2006 17:13:17 -0800 (PST)
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From: Stephen Hemminger <shemminger@osdl.org>
Date: Wed, 6 Dec 2006 16:58:35 -0800

> The more robust way would be to stop the queue (like flow control)
> and return busy. You would need a timer though to handle the case
> where some disk i/o stole all the mappings and then network device flow
> blocked.

You need some kind of fairness, yes, that's why I suggested a
callback.  When your DMA allocation fails, you get into the rear of
the FIFO, when a free occurs, we callback starting from the head of
the FIFO.  You don't get removed from the FIFO unless at least one of
your DMA allocation retries succeed.