linux-kernel - Re: sg_set_page not usable for .bss?

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Message-Id: <20081201.161026.234536822.davem@davemloft.net>
Date:	Mon, 01 Dec 2008 16:10:26 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	jengelh@...ozas.de
Cc:	john.haxby@...cle.com, netfilter-devel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: sg_set_page not usable for .bss?

From: Jan Engelhardt <jengelh@...ozas.de>
Date: Mon, 1 Dec 2008 23:40:18 +0100 (CET)

> 
> On Monday 2008-12-01 23:02, John Haxby wrote:
> >>>+	sg_init_table(sg, 2);
> >>>+	sg_set_buf(&sg[0], data, n);
> >>>+	strcpy(digest_password, sysrq_password);
> >>>+	i = strlen(digest_password);
> >>>+	sg_set_buf(&sg[1], digest_password, i);
> >>
> >> Could we directly use sysrq_password instead of copying it to
> >> digest_password first?
> >
> > No :-)   Eventually I discovered the reason my code wasn't working
> > boils down to the definition of sg_set_buf:
> >
> >   sg_set_page(sg, virt_to_page(buf), buflen, offset_in_page(buf))
> >
> > which doesn't work for sysrq_password.   I don't know why I'll
> > double check.
> 
> Well, sysrq_password is in the .bss section, where as digest_password
> is on the heap due to being kmalloc'ed. Maybe that makes a difference?
> Someone more versed with the virtual memory layer might know.

You can't use these interfaces on kernel image addresses.
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