does the linux support rootfs on vfat?

does the linux support rootfs on vfat?

[zhuzhenhua]

if in my product based ide disk, i want to it to support the
u-disk(with vfat fs), and can i set the root fs as vfat too?
if use vfat as rootfs, what's disadvantage of the selection?


Best Regards

Zhuzhenhua

Re: does the linux support rootfs on vfat?

[Jan-Benedict Glaw]

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On Sun, 2006-03-05 14:17:56 +0800, zhuzhenhua <zzh.hust@gmail.com> wrote:
> if in my product based ide disk, i want to it to support the
> u-disk(with vfat fs), and can i set the root fs as vfat too?
> if use vfat as rootfs, what's disadvantage of the selection?

Well, most notably you won't have device nodes. Maybe a ram-backed
filesystem mounted to /dev/ could solve that, but you'd probably need
an initrd for that to do.

MfG, JBG

-- 
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Re: does the linux support rootfs on vfat?

[Ralf Baechle]

On Sun, Mar 05, 2006 at 09:09:58AM +0100, Jan-Benedict Glaw wrote:

> On Sun, 2006-03-05 14:17:56 +0800, zhuzhenhua <zzh.hust@gmail.com> wrote:
> > if in my product based ide disk, i want to it to support the
> > u-disk(with vfat fs), and can i set the root fs as vfat too?
> > if use vfat as rootfs, what's disadvantage of the selection?
> 
> Well, most notably you won't have device nodes. Maybe a ram-backed
> filesystem mounted to /dev/ could solve that, but you'd probably need
> an initrd for that to do.

It's anso case-insensitive which may cause some further troubles.  It's
doesn't have proper inodes, no UNIX file modes, no UID / GID support (These
two can be kludges in awfully insufficient way through mount options), not
only lacks device special files but also no FIFO, no UNIX domain sockets,
no hard or soft links.  It's simply a sorry excuse for a useful filesystem.

  Ralf

Re: does the linux support rootfs on vfat?

[Geoff Levand]

Ralf Baechle wrote:
> On Sun, Mar 05, 2006 at 09:09:58AM +0100, Jan-Benedict Glaw wrote:
> 
>> On Sun, 2006-03-05 14:17:56 +0800, zhuzhenhua <zzh.hust@gmail.com> wrote:
>> > if in my product based ide disk, i want to it to support the
>> > u-disk(with vfat fs), and can i set the root fs as vfat too?
>> > if use vfat as rootfs, what's disadvantage of the selection?
>> 
>> Well, most notably you won't have device nodes. Maybe a ram-backed
>> filesystem mounted to /dev/ could solve that, but you'd probably need
>> an initrd for that to do.
> 
> It's anso case-insensitive which may cause some further troubles.  It's
> doesn't have proper inodes, no UNIX file modes, no UID / GID support (These
> two can be kludges in awfully insufficient way through mount options), not
> only lacks device special files but also no FIFO, no UNIX domain sockets,
> no hard or soft links.  It's simply a sorry excuse for a useful filesystem.

It's attractive for a limited resource device that needs to have FAT support
for a removable flash memory card (for Windows PC interoperability).  If you
can use FAT for the root fs, that reduces the system resource needs.

It doesn't make sense if his ide disk is non-removable though.

-Geoff

Re: does the linux support rootfs on vfat?

[P. Christeas]

On Monday 06 March 2006 6:49 pm, you wrote:
> It's attractive for a limited resource device that needs to have FAT
> support for a removable flash memory card (for Windows PC
> interoperability).  If you can use FAT for the root fs, that reduces the
> system resource needs.
>
> It doesn't make sense if his ide disk is non-removable though.
>

IMHO it is a bad idea alltogether. You are asking for trouble. The system 
resource needs are rather increased [1] than decreased. 
On the other hand, you would you need to trade files between the *root* fs of 
the linux and Windoze? Usually we want to trade some user files (like photos, 
music etc.), but not the system files. Would you trust Windoze ever not to 
destroy something in those root files? Why don't you create a second, VFAT 
partition and mount it somewhere?

[1] ext2 or whatever is optimized. FAT isn't so and you really want to run 
Linux trivial files from an optimized system.

Re: does the linux support rootfs on vfat?

[Stuart Longland]

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(Gah... I meant this to be sent publically, not just privately ;-)

zhuzhenhua wrote:
> if in my product based ide disk, i want to it to support the
> u-disk(with vfat fs), and can i set the root fs as vfat too?
> if use vfat as rootfs, what's disadvantage of the selection?

In theory, you could... BUT... FAT32 (and every other FAT variant) lacks:

- Ownership metadata (uid/gid fields)
- Permissions (mode: read/write/execute/sticky/suid/sgid)
- Links (both hard-links and symbolic links)
... probably character devices, block devices, pipes and other numerous
devices that 99.999999% of distributions rely on.

Now, there is UMSDOS, which uses additional special files to emulate
these on top of a standard MS-DOS filesystem ... mind you, it predates
VFAT by many years, and so I'm not sure what it's support is like for
long filenames.  I also haven't seen it in the kernel File System menu
for some time now.

I'd recommend using an external initrd... or an initramfs-based kernel.
 That way it's just one or two files, not one or two hundred. ;-)
-- 
Stuart Longland (aka Redhatter)              .'''.
Gentoo Linux/MIPS Cobalt and Docs Developer  '.'` :
. . . . . . . . . . . . . . . . . . . . . .   .'.'
http://dev.gentoo.org/~redhatter             :.'

International Asperger's Year (1906 ~ 2006)
http://dev.gentoo.org/~redhatter/iay


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Re: does the linux support rootfs on vfat?

[Geoff Levand]

zhuzhenhua wrote:
> if in my product based ide disk, i want to it to support the
> u-disk(with vfat fs), and can i set the root fs as vfat too?
> if use vfat as rootfs, what's disadvantage of the selection?
> 

See these threads, 'Posix file attribute support on VFAT', which
disscusses using VFAT for a root fs:

  http://lkml.org/lkml/2005/8/8/76
  http://lkml.org/lkml/2005/8/8/326

-Geoff