netdev - Re: [PATCH 1/2] net: tcp_header_len_th and tcp_option_len

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Date:	Tue, 12 Jan 2010 12:42:04 -0500
From:	William Allen Simpson <william.allen.simpson@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	Linux Kernel Developers <linux-kernel@...r.kernel.org>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Michael Chan <mchan@...adcom.com>
Subject: Re: [PATCH 1/2] net: tcp_header_len_th and tcp_option_len_th

Eric Dumazet wrote:
> Its better to inline your patches so that we can comment them, without copy/paste
> 
> When I hit 'reply to', my mailer only quoted the ChangeLog, not the patch.
> 
Seeing that we're both using Mozilla, how to you do it?

It took me many attempts to get this to work with Thunderbird on the Mac.


> Anyway ..
> 
> +/* Length of standard options only.  This could be negative. */
> +static inline int tcp_option_len_th(const struct tcphdr *th)
> +{
> +	return (int)(th->doff * 4) - sizeof(*th);
> +}
> 
> 
> The (int) cast is not necessary, since the function returns a signed int
> 
> ->
> 	return th->doff * 4 - sizeof(*th);
> 
Then GCC must be smarter than it was in the past, as doff is an __u16
bit slice -- once upon a time, a cast was required before subtraction.
One of the dis/advantages of C programming for 30+ years is that my
fingers remember some fairly old practices....

(But this still works properly!)

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