linux-kernel - question on type conversions in show_map

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Message-ID: <4B16B32D.9030106@nortel.com>
Date:	Wed, 02 Dec 2009 12:34:21 -0600
From:	"Chris Friesen" <cfriesen@...tel.com>
To:	LKML <linux-kernel@...r.kernel.org>
Subject: question on type conversions in show_map_vma()

Another developer and I were looking at show_map_vma() and started
wondering about the "pgoff" value:

pgoff = ((loff_t)vma->vm_pgoff) << PAGE_SHIFT;

Here we take a variable of type "unsigned long", we cast it to "long
long", shift it, then assign the result to a variable of type "unsigned
long long".

I realize that there isn't any danger of invalid sign extension, but it
does seem a bit odd to be casting to a signed value when the result is
going to be unsigned.

Is there a historical reason why pgoff is unsigned rather than just of
type "loff_t"?

Chris
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