linux-kernel - Re: [RFC 2/2] initramfs with digital signature protection

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Message-ID: <6b31c4f9-d98c-42fc-a510-39bf536b3299@email.android.com>
Date:	Fri, 08 Feb 2013 07:49:26 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"Kasatkin, Dmitry" <dmitry.kasatkin@...el.com>
CC:	Peter Jones <pjones@...hat.com>,
	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 2/2] initramfs with digital signature protection

Yes, but you can't umount rootfs.

"Kasatkin, Dmitry" <dmitry.kasatkin@...el.com> wrote:

>On Wed, Feb 6, 2013 at 6:41 PM, H. Peter Anvin <hpa@...or.com> wrote:
>> The cleanup is not a umount, it is actually a tree walk unlinking the
>contents.
>>
>
>Please see that umounting ramfs releases the memory.
>There was no forced cleanup.
>"cp" copied about 2GB of content.
>After umounting we got 2GB back to free RAM...
>
>kds@kds:~$ sudo mount -t ramfs testramfs /test
>kds@kds:~$ sudo cp -r /usr/ /test
>kds@kds:~$ du -sm /test
>2154    /test
>kds@kds:~$ free
>                       total       used            free     shared
>buffers     cached
>Mem:       8058600    7855780     202820          0      24768   
>4819136
>-/+ buffers/cache:    3011876    5046724
>Swap:            0          0          0
>kds@kds:~$ sudo umount /test
>kds@kds:~$ free
>                      total       used            free     shared
>buffers     cached
>Mem:       8058600    5644864    2413736          0      25268   
>2623956
>-/+ buffers/cache:    2995640    5062960
>Swap:            0          0          0
>
>The same happens also with tmpfs.
>
>- Dmitry
>
>> "Kasatkin, Dmitry" <dmitry.kasatkin@...el.com> wrote:
>>
>>>On Wed, Feb 6, 2013 at 7:04 AM, H. Peter Anvin <hpa@...or.com> wrote:
>>>> On 02/05/2013 02:09 PM, Kasatkin, Dmitry wrote:
>>>>>
>>>>>
>>>>> It should not be like that. Actually when pre-init exits, cleanup
>>>code
>>>>> umount tmpfs, which in turn cleanups the RAM.
>>>>>
>>>>
>>>> It doesn't quite... the rootfs is permanent.  This is also only one
>>>usage
>>>> mode: there are quite a few Linux systems running directly out of
>>>initramfs.
>>>>
>>>
>>>rootfs is not permanent when it is ramfs. It is cleaned up on switch
>>>root.
>>>It is easy to find out that it is empty by mounting : mount -t ramfs
>>>rootfs /mnt/
>>>
>>>In the case of running from normal storage, of course, there is
>>>ridicules remove the content.
>>>
>>>- Dmitry
>>>
>>>
>>>>         -hpa
>>>>
>>>>
>>>> --
>>>> H. Peter Anvin, Intel Open Source Technology Center
>>>> I work for Intel.  I don't speak on their behalf.
>>>>
>>
>> --
>> Sent from my mobile phone. Please excuse brevity and lack of
>formatting.

-- 
Sent from my mobile phone. Please excuse brevity and lack of formatting.
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