Re: sg_set_page not usable for .bss?

[David Miller <davem@davemloft.net>]

From: Jan Engelhardt <jengelh@medozas.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.