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

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Date:	Mon, 2 Sep 2013 19:55:10 +0800
From:	Zheng Liu <gnehzuil.liu@...il.com>
To:	Robert Yang <liezhi.yang@...driver.com>
Cc:	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 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?

                                                - Zheng
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