linux-kernel - Re: usbmon: size of different fields?

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Message-ID: <20101109075056.59a2e7d8@lembas.zaitcev.lan>
Date:	Tue, 9 Nov 2010 07:50:56 -0700
From:	Pete Zaitcev <zaitcev@...hat.com>
To:	Németh Márton <nm127@...email.hu>
Cc:	linux-usb@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	Developer support list for Wireshark 
	<wireshark-dev@...eshark.org>, zaitcev@...hat.com
Subject: Re: usbmon: size of different fields?

On Tue, 09 Nov 2010 07:40:36 +0100
Németh Márton <nm127@...email.hu> wrote:

> I'm looking at the struct mon_bin_hdr and struct mon_bin_isodesc in file
> f=drivers/usb/mon/mon_bin.c

Actually you're supposed to be looking at Documentation/usb/usbmon.txt.
If there is a discrepancy between the usbmon.txt and mon_bin.c, I want
to know about it.

> As far as I understand u64, s64, u32 and s32 have always fixed bit lengths.
> 
> What about "unsigned char", "char", "unsigned int" and "int"? May their size in bits
> differ in different architecture?

No they may not. They sizes are always the same on any architecture,
as long as Linux supports it.

> I'm asking this because I was dealing with the USB packet dissectors for Wireshark
> and it is possible to capture the USB traffic on one computer and then transfer
> the file to another computer.

Do be careful here, because the struct you're talking about is a part
of API, not a network stream. Its field sizes are rigidly defined, but
the byte order is host! You MUST NOT attempt to store it in pcap files.

-- Pete
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