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Date:      Sun, 30 Dec 2007 17:11:16 +0000 (GMT)
From:      Robert Watson <rwatson@FreeBSD.org>
To:        Tofig Suleymanov <tofig@freebsd.az>
Cc:        freebsd-net@freebsd.org
Subject:   Re: if_start running deferred for Giant
Message-ID:  <20071230170217.T6382@fledge.watson.org>
In-Reply-To: <4777690B.1030403@freebsd.az>
References:  <4777690B.1030403@freebsd.az>

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On Sun, 30 Dec 2007, Tofig Suleymanov wrote:

> I am writing a driver for Kyocera USB modem for FreeBSD and there are a few 
> questions that I am not able to solve alone. I would be grateful if someone 
> could point me into the right direction.Here is the first one:
>
> Inside the USB_ATTACH() function I initialise the ifnet(9) structure and 
> return USB_ATTACH_SUCCESS_RETURN. Everything seems to be fine so far (I can 
> see the interface in ifconfig output) except the following error notice spit 
> to the console:
>
> xxxxxx kernel: ib0: if_start running deferred for Giant
>
> I am not sure what does this exactly mean.
>
> Any help would be appreciated.

This occurs when a network device driver has declared itself IFF_NEEDSGIANT -- 
that is, has declared that it requires the Giant lock in order to operate. 
As this is considered an undesirable state of affairs for a device driver, a 
warning is printed.  However, in the case of a USB device driver, it is 
currently required as the USB framework is not MPSAFE, so requires Giant.

Robert N M Watson
Computer Laboratory
University of Cambridge



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