Syslinux - Nov 2014 - [RFC] make extlinux work without mount the filesystem

Hello syslinux,

I'm a newbie to extlinux, and I'm a developer from yocto project
(an embedded linux project).

The device or filesystem must be mounted before we can install the
bootsector to the device if I understand correctly, for example:

$ mount /dev/sdcX /tmp/mnt
$ extlinux -i /tmp/mnt

Usually, the mount command requires the root privilage, we may not
have the root privilage when we work on a shared server.

And in embedded linux development, usually, we need deploy the system
on an file block (not a real device partition), for example:

$ dd if=/dev/zero of=test.img count=100k bs=1k
$ mke2fs -t ext3 -F test.img

It would be great to have something like: (suppose we have a
"-d/--device"
option)
$ extlinux -i -d test.img

then the bootsector will be installed without mount the test.img

I had added something similar to e2fsprogs' mke2fs: (on master branch)
http://git.kernel.org/cgit/fs/ext2/e2fsprogs.git/log/

which can copy files into test.img without mount it, for example:
$ mke2fs -t ext3 -d <rootfs_dir> -F test.img

I'd like to make extlinux can work without mount the filesystem (use
libext2fs), is it possible for extlinux, please ? And is such a patch
acceptable, please ? (Add a "-d/--device <device>" option, and
the
option is optional).

Any comments is appreciated.

-- 
Thanks

Robert

On 11/20/2014 10:21 PM, Robert Yang wrote:
>
> which can copy files into test.img without mount it, for example:
> $ mke2fs -t ext3 -d <rootfs_dir> -F test.img
>
> I'd like to make extlinux can work without mount the filesystem (use
> libext2fs), is it possible for extlinux, please ? And is such a patch
> acceptable, please ? (Add a "-d/--device <device>" option,
and the
> option is optional).
>
I would definitely accept such a patch.  It probably makes more sense in 
the "syslinux" installer rather than "extlinux", since the
former
already operates on an unmounted filesystem.

I would also love to unify the FAT implementation.

	-hpa

On 11/21/2014 02:33 PM, H. Peter Anvin wrote:
> On 11/20/2014 10:21 PM, Robert Yang wrote:
>>
>> which can copy files into test.img without mount it, for example:
>> $ mke2fs -t ext3 -d <rootfs_dir> -F test.img
>>
>> I'd like to make extlinux can work without mount the filesystem
(use
>> libext2fs), is it possible for extlinux, please ? And is such a patch
>> acceptable, please ? (Add a "-d/--device <device>"
option, and the
>> option is optional).
>>
>
> I would definitely accept such a patch.  It probably makes more sense in
the
> "syslinux" installer rather than "extlinux", since the
former already operates
> on an unmounted filesystem.
Great, thanks for the reply, I will do more investigations on syslinux/extlinux,
and ask for help or send a draft design later.

// Robert
>
> I would also love to unify the FAT implementation.
>
>      -hpa
>
>
>
>

(snip)
> It probably makes more sense in 
> the "syslinux" installer rather than "extlinux", since
the former
> already operates on an unmounted filesystem.
> 
 
In other words, the Linux-based "syslinux" installers could / would 
support ext2/3/4 too.

In particular, the (./bios/mtools/) "syslinux" command does not need 
special permissions (other than write), but it needs "something" else 
instead (e.g. "mtools" for FAT), and it can use the
"--offset"
parameter.

This could mean, to either:
_ modify the current installers; or,
_ add a new (./bios/mke2/) {sys,ext}linux installer (the path and file 
name could be something else; I am focusing on the generic idea).

Regards,
Ady.