linux-kernel - sg_set_page not usable for .bss?

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Date:	Mon, 1 Dec 2008 23:40:18 +0100 (CET)
From:	Jan Engelhardt <jengelh@...ozas.de>
To:	John Haxby <john.haxby@...cle.com>
cc:	Netfilter Development Mailinglist 
	<netfilter-devel@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: sg_set_page not usable for .bss?


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.

>+static char sysrq_password[64];
>[...]
>+	digest_password = kmalloc(sizeof(sysrq_password), GFP_KERNEL);
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