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Re: [lwip-users] link down and netconn problem

From: Kieran Mansley
Subject: Re: [lwip-users] link down and netconn problem
Date: Tue, 06 Oct 2009 14:31:51 +0100

On Tue, 2009-10-06 at 14:17 +0200, Martin Velek wrote:
> Hello,
> my EMAC driver is capable to detect link down(unplugging eth. cable).
> This situation is returned in low_level_output by ERR_IF and
> netif->flags &= ~NETIF_FLAG_LINK_UP. This is a normal behavior,
> netconn_sendto returns ERR_IF.
> However after plugging cable and sending next packet, this operation
> fails also with ERR_IF. I have tried to trace programm and this is a
> sequence of called functions:
> netconn_sendto
> netconn_send
> do_send - return.
> The first line of do_send function contains "if
> (!ERR_IS_FATAL(msg->conn->err)) " that causes return without checking
> the line status.
> Does it mean, that before any netconn_sendto I should set conn->err to ERR_OK?

ERR_IF is deemed to be a fatal error: one from which the connection
cannot recover.  Clearly in your case this is wrong: unplugging and
replugging the cable is not a permanent state so not a fatal error.
What we probably need to do is split ERR_IF into two: one to describe
fatal errors such as not being able to add the netif, and another
describing transient errors such as the link going down.  Your
low_level_output could then return whichever of these is appropriate.

On a related note, does anyone know why ERR_INPROGRESS is fatal?  I
don't think it should be.


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