linux-ext4 - Re: [RFC 00/10] e2fsprogs/mke2fs: add an option: -d root-directory

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Date:	Mon, 2 Sep 2013 20:20:02 +0800
From:	Robert Yang <liezhi.yang@...driver.com>
To:	<linux-ext4@...r.kernel.org>, <tytso@....edu>,
	<dvhart@...ux.intel.com>
Subject: Re: [RFC 00/10] e2fsprogs/mke2fs: add an option: -d root-directory



On 09/02/2013 07:55 PM, Zheng Liu wrote:
> On Mon, Sep 02, 2013 at 02:46:33PM +0800, Robert Yang wrote:
>>
>>
>> On 09/01/2013 11:26 AM, Zheng Liu wrote:
>>> Hi Robert,
>>>
>>> On Wed, Aug 28, 2013 at 01:25:50PM +0800, Robert Yang wrote:
>>>> This option is used for adding the files from the root-directory to the
>>>> filesystem, it is similiar to genext2fs, but genext2fs doesn't fully
>>>> support ext4.
>>>>
>>>> * Questions
>>>>    - Is such an option acceptable ?
>>>>
>>>>    - Most of the code have been in debugfs/debugfs.c already, I moved them to
>>>>      misc/util.c and modified them to let both mke2fs and debugfs can use them,
>>>>      maybe we should put these code in another separate file ?
>>>>
>>>>    - Where can I get the up-to-date development git repo, please? I think that
>>>>      there would be conflicts with the dev git repo, I'd like to rebase it if I
>>>>      can get the repo, currently, I'm using this one:
>>>>
>>>>      http://git.kernel.org/cgit/fs/ext2/e2fsprogs.git
>>>>
>>>> * The size impact on misc/mke2fs:
>>>>     1,677,297 -> 1,728,110 (non stripped, about 50K increases)
>>>>     316,968 -> 325,160 (stripped, 8K increases)
>>>>
>>>> Please feel free to give your comments.
>>>
>>> If I understand correctly, after applied this patch set, we can copy
>>> some files from a directory that is indicated by '-d' option when we
>>> create a new ext4 file system.  My concern is why we need to add this
>>> option?  Without this option I can use 'mkfs.ext4 ${DEV}', 'mount ${DEV}
>>> ${MNT}' and 'cp ${SRC} ${MNT}' to do the same thing.  I am not
>>> convinced.  Could you please describe more details for this patch set?
>>>
>>
>> Hi Zheng,
>>
>> Yes, you are right, we can run mkfs/mount/cp to do the same thing,
>> but the problem is that the "mount" command requires the root privilege,
>> but we may not have it when we are working on a sever (the mkfs doesn't
>> need the root privilege), for example
>>
>> $ dd if=/dev/zero of=test.img count=0 bs=1k seek=2M
>> $ mke2fs -t ext4 -F test.img -d <root-dir>
>>
>> Will create an ext4 image with the files copied without the root privilege.
>
> Interesting.  As you said above, if you haven't the root privilege, you
> won't use this file system.  But at least this file system will be used
> by some one who have the root privilege.  He/she can do the rest of
> works.  That means that you do 'dd/mke2fs' and he or she does
> 'mount/cp'.  I don't see any reason that all dirs and files must be
> created by mke2fs.  Any real case that needs to do this?
>

Hi Zheng,

For example, in Linux embedded development, we usually create a filesystem
image which contains the linux embedded OS, this image can be used by qemu,
Live CD and so on.

// Robert

>                                                  - Zheng
>
>
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