msdos/vfat defaults are annoying

msdos/vfat defaults are annoying

[John Richard Moser]

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So I've noticed, again, much annoyed, that if I rely on -t auto,
horrible horrible things happen.

I have had floppies and compact flash cards that I've done mkfs.vfat to
make fat32 filesystems on (not fat16), and mounting them brings the
thing on as msdos by default (autodetect).  Furthermore, I build msdos
out, and mount says the msdos FS isn't supported.  In either case I need
to use -t vfat.

Vfat is much more common and should be backwards compatible with msdos.
  When there's a ton of foo~1 files around after mounting, something's
wrong.

Shouldn't vfat be the automatic default?  Or at least, if only vfat and
not msdos is available, use vfat.  For that matter, can msdos and vfat
be collapsed?  As I recall, the difference is that vfat makes more
inodes to store long file names, one for each 13 characters (in reverse?)

I dunno.  I can never understand the innards of the kernel devs' minds.

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Re: msdos/vfat defaults are annoying

[Christoph Hellwig]

On Sun, Feb 06, 2005 at 12:33:43AM -0500, John Richard Moser wrote:
> I dunno.  I can never understand the innards of the kernel devs' minds.

filesystem detection isn't handled at the kerne level.

Re: msdos/vfat defaults are annoying

[Michelle Konzack]

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Hello John,

Am 2005-02-06 00:33:43, schrieb John Richard Moser:

> So I've noticed, again, much annoyed, that if I rely on -t auto,
> horrible horrible things happen.

Maybe you add the file

  __( '/etc/filesystems' )______________________________________________
 /
|       ext3
|       ext2
|       minix
|       vfat
|       msdos
|       iso9660
|       hfsplus
|       hfs
| nodev	proc
 \______________________________________________________________________

and if you use 'mount -t auto ...' it
will try the filesystems in this order.

Greetings
Michelle

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Michelle Konzack   Apt. 917                  ICQ #328449886
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Re: msdos/vfat defaults are annoying

[John Richard Moser]

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Christoph Hellwig wrote:
> On Sun, Feb 06, 2005 at 12:33:43AM -0500, John Richard Moser wrote:
> 
>>I dunno.  I can never understand the innards of the kernel devs' minds.
> 
> 
> filesystem detection isn't handled at the kerne level.
> 

o_o

. . . then I shall bug baselayout@!
> 

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[PATCH] Re: msdos/vfat defaults are annoying

[Pozsar Balazs]

On Sun, Feb 06, 2005 at 07:06:59AM +0000, Christoph Hellwig wrote:
> On Sun, Feb 06, 2005 at 12:33:43AM -0500, John Richard Moser wrote:
> > I dunno.  I can never understand the innards of the kernel devs' minds.
> 
> filesystem detection isn't handled at the kerne level.

Yeah, but the link order could be changed... Patch inlined.

-- 
pozsy

diff -Naurd a/fs/Makefile b/fs/Makefile
--- a/fs/Makefile	2004-08-04 10:52:28.000000000 +0200
+++ b/fs/Makefile	2004-08-04 11:32:04.510913663 +0200
@@ -57,8 +57,8 @@
 obj-$(CONFIG_MINIX_FS)		+= minix/
 obj-$(CONFIG_FAT_FS)		+= fat/
 obj-$(CONFIG_UMSDOS_FS)		+= umsdos/
-obj-$(CONFIG_MSDOS_FS)		+= msdos/
 obj-$(CONFIG_VFAT_FS)		+= vfat/
+obj-$(CONFIG_MSDOS_FS)		+= msdos/
 obj-$(CONFIG_BFS_FS)		+= bfs/
 obj-$(CONFIG_ISO9660_FS)	+= isofs/
 obj-$(CONFIG_DEVFS_FS)		+= devfs/

Signed-off-by: Pozsar Balazs <pozsy@uhulinux.hu>

Re: [PATCH] Re: msdos/vfat defaults are annoying

[Al Viro]

On Mon, Feb 07, 2005 at 12:21:08AM +0100, Pozsar Balazs wrote:
> On Sun, Feb 06, 2005 at 07:06:59AM +0000, Christoph Hellwig wrote:
> > On Sun, Feb 06, 2005 at 12:33:43AM -0500, John Richard Moser wrote:
> > > I dunno.  I can never understand the innards of the kernel devs' minds.
> > 
> > filesystem detection isn't handled at the kerne level.
> 
> Yeah, but the link order could be changed... Patch inlined.

And just what does the link order (or changes thereof) have to do with that?

Re: [PATCH] Re: msdos/vfat defaults are annoying

[Pozsár Balázs]

On Mon, Feb 07, 2005 at 12:36:10AM +0000, Al Viro wrote:
> On Mon, Feb 07, 2005 at 12:21:08AM +0100, Pozsar Balazs wrote:
> > On Sun, Feb 06, 2005 at 07:06:59AM +0000, Christoph Hellwig wrote:
> > > On Sun, Feb 06, 2005 at 12:33:43AM -0500, John Richard Moser wrote:
> > > > I dunno.  I can never understand the innards of the kernel devs' minds.
> > > 
> > > filesystem detection isn't handled at the kerne level.
> > 
> > Yeah, but the link order could be changed... Patch inlined.
> 
> And just what does the link order (or changes thereof) have to do with that?

IIRC currently if both msdos and vfat are compiled in (not modules), and 
you try to mount a vfat filesystem without explicitly specifying the fs 
type, it will be mounted with the msdos type. With the, it will mounted 
vfat.


-- 
pozsy

Re: [PATCH] Re: msdos/vfat defaults are annoying

[Nuno Monteiro]

On 2005.02.07 00:42, Pozsár Balázs wrote:
> On Mon, Feb 07, 2005 at 12:36:10AM +0000, Al Viro wrote:
> > On Mon, Feb 07, 2005 at 12:21:08AM +0100, Pozsar Balazs wrote:
> > > On Sun, Feb 06, 2005 at 07:06:59AM +0000, Christoph Hellwig wrote:
> > > > filesystem detection isn't handled at the kerne level.
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

> 
> IIRC currently if both msdos and vfat are compiled in (not modules),  
> and
> 
> you try to mount a vfat filesystem without explicitly specifying the fs
> type, it will be mounted with the msdos type. With the, it will mounted
> vfat.
>


But since filesystem detection isn't handled in the kernel, changing the  
link order is pointless. Please fix your /etc/filesystems instead.

~# grep camera /etc/fstab
/dev/sda1 /mnt/camera auto users,noauto 0 0
~# strace -o mount.trace mount /mnt/camera
~# grep filesystems mount.trace
open("/etc/filesystems", O_RDONLY|O_LARGEFILE) = 3
~# cat /etc/filesystems
ext2
ext3
nodev proc
nodev devpts
iso9660
reiserfs
vfat
udf

Also check man 8 mount, specifically option -t:

[...] Creating a  file /etc/filesystems can be useful to change the probe  
order (e.g., to try vfat before msdos) ...

This is from man-pages 1.66, btw.


Regards,


		Nuno

Re: [PATCH] Re: msdos/vfat defaults are annoying

[Clemens Schwaighofer]

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On 02/07/2005 09:36 AM, Al Viro wrote:
> On Mon, Feb 07, 2005 at 12:21:08AM +0100, Pozsar Balazs wrote:
> 
>>On Sun, Feb 06, 2005 at 07:06:59AM +0000, Christoph Hellwig wrote:
>>
>>>On Sun, Feb 06, 2005 at 12:33:43AM -0500, John Richard Moser wrote:
>>>
>>>>I dunno.  I can never understand the innards of the kernel devs' minds.
>>>
>>>filesystem detection isn't handled at the kerne level.
>>
>>Yeah, but the link order could be changed... Patch inlined.
> 
> 
> And just what does the link order (or changes thereof) have to do with that?

because some distributions (eg gentoo) make a symlink to /proc/filesystems

jupiter root # ls -l /etc/filesystems
lrwxrwxrwx  1 root root 19 Oct 25 11:18 /etc/filesystems ->
../proc/filesystems

and then its impossible to change the order. (unless you make a "hand
made" file of course).

- --
[ Clemens Schwaighofer                      -----=====:::::~ ]
[ TBWA\ && TEQUILA\ Japan IT Group                           ]
[                6-17-2 Ginza Chuo-ku, Tokyo 104-0061, JAPAN ]
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Re: [PATCH] Re: msdos/vfat defaults are annoying

[Pozsár Balázs]

On Mon, Feb 07, 2005 at 02:48:00AM +0000, Nuno Monteiro wrote:
> 
> On 2005.02.07 00:42, Pozsár Balázs wrote:
> >On Mon, Feb 07, 2005 at 12:36:10AM +0000, Al Viro wrote:
> >> On Mon, Feb 07, 2005 at 12:21:08AM +0100, Pozsar Balazs wrote:
> >> > On Sun, Feb 06, 2005 at 07:06:59AM +0000, Christoph Hellwig wrote:
> >> > > filesystem detection isn't handled at the kerne level.
>        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

> But since filesystem detection isn't handled in the kernel, changing the  
> link order is pointless. Please fix your /etc/filesystems instead.

But the contents of /proc/filesystems comes from the kernel. And the 
order of filesystems comes from the link order.

Let me show you, why it is _not_ pointless:
If you do not have /etc/filesystems, mount will read /proc/filesystems:

# strace -o mount.trace mount -t auto /dev/sda1 /mnt
# grep filesystems mount.trace
open("/etc/filesystems", O_RDONLY|O_LARGEFILE) = -1 ENOENT (No such file or directory)
open("/proc/filesystems", O_RDONLY|O_LARGEFILE) = 3
# grep ^mount mount.trace
mount("/dev/sda1", "/mnt", "squashfs", 0xc0ed0000, 0) = -1 EINVAL (Invalid argument)
mount("/dev/sda1", "/mnt", "vfat", 0xc0ed0000, 0) = 0

See? I _have_ that patch applied, that's why it tried vfat and not msdos 
first.

Granted, I could override the default order by using a /etc/filesystems 
file. But the kernel should have a much more sane default on its own, 
namely "try vfat before msdos".



-- 
pozsy

Re: [PATCH] Re: msdos/vfat defaults are annoying

[Andries Brouwer]

On Mon, Feb 07, 2005 at 03:53:00PM +0900, Clemens Schwaighofer wrote:

> >>Yeah, but the link order could be changed... Patch inlined.
> > 
> > And just what does the link order (or changes thereof) have to do with that?
> 
> because some distributions (eg gentoo) make a symlink to /proc/filesystems
> 
> jupiter root # ls -l /etc/filesystems
> lrwxrwxrwx  1 root root 19 Oct 25 11:18 /etc/filesystems ->
> ../proc/filesystems
> 
> and then its impossible to change the order. (unless you make a "hand
> made" file of course).

Ah, I had not met this particular form of brokenness before.

If one does not specify a filesystem type to mount,
mount will try its own collection of heuristics, looking for
known magic numbers. This stuff comes in two versions, depending
on whether mount was linked against the blkid library or not.

When no magic is recognized, mount will try all filesystems
listed in /proc/filesystems that were not rejected already
because of wrong magic. The list in /proc/filesystems can
be overridden by the file /etc/filesystems. That is useful
for two reasons: (i) sometimes the kernel crashes when one
tries to mount something with the wrong type, so
/etc/filesystems can skip the types that must never be tried,
and (ii) sometimes several types would succeed (e.g. msdos/vfat)
and the user can override the kernel order.

Making a symlink /etc/filesystems -> /proc/filesystems is
meaningless.

By the way, it is best to consider the kernel order as undefined.
It plays a role when mounting the rootfs. If you get undesirable
results at boot time, specify the rootfstype= boot option.
It plays a role when generating /proc/filesystems.
If you get undesirable results, adapt /etc/filesystems.

It is not true that vfat is universally better than msdos.
Some need one, some need the other.

Instead of having a global order, one can have a per-mountpoint
list in /etc/fstab. For example,

/dev/foo	/mnt	ext2,msdos	noauto	0 0

Finally, guessing is always bad. It is convenient in the short run
but may lead to crashes and data loss in the long run.

Andries

Re: [PATCH] Re: msdos/vfat defaults are annoying

[Pozsár Balázs]

On Mon, Feb 07, 2005 at 12:29:14PM +0100, Andries Brouwer wrote:
> and (ii) sometimes several types would succeed (e.g. msdos/vfat)
> and the user can override the kernel order.

But we are talking about the default order.


> By the way, it is best to consider the kernel order as undefined.

But it is not undefined, and if it is a well-defined order (and it is), 
then it should have a sane order.

> It is not true that vfat is universally better than msdos.
> Some need one, some need the other.

> Finally, guessing is always bad. It is convenient in the short run
> but may lead to crashes and data loss in the long run.

Well, it can be bad, maybe it should be avoided. But if someone wants 
guessing, why not provide him a (imho) more reasonable order of 
guessing? I do think vfat should be tried first. If you are doing for 
example some kind of recovery you wont bet on autoguessing. But if you 
just want to use it, use might, and in that case you want long 
filenames, ie vfat.


-- 
pozsy

Re: [PATCH] Re: msdos/vfat defaults are annoying

[Michelle Konzack]

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Am 2005-02-07 09:47:09, schrieb Pozsár Balázs:

> See? I _have_ that patch applied, that's why it tried vfat and not msdos 
> first.

With this, you will nerver mount a Filesystem "msdos".

Because "vfat" IS "msdos" + "lfn".

You can attach to ALL "msdos" media "lfn" and you will have "vfat".

> Granted, I could override the default order by using a /etc/filesystems 
> file. But the kernel should have a much more sane default on its own, 
> namely "try vfat before msdos".

This will give many errors here at work...

Greetings
Michelle

-- 
Linux-User #280138 with the Linux Counter, http://counter.li.org/ 
Michelle Konzack   Apt. 917                  ICQ #328449886
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Re: [PATCH] Re: msdos/vfat defaults are annoying

[Clemens Schwaighofer]

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On 07.02.2005 20:29, Andries Brouwer wrote:

> Making a symlink /etc/filesystems -> /proc/filesystems is
> meaningless.

well to be honest, I didn't even know Gentoo makes a symlink here, but
I'll definitly will make bug entry for that.

Perhaps its a default setting. eg Debian doesn't have a /etc/filesystems
file by defauly anyway.

> It is not true that vfat is universally better than msdos.
> Some need one, some need the other.

but to be honest, most times I need vfat, and I actually haven't
encountered a time when I need msdos.

lg, clemens

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Re: [PATCH] Re: msdos/vfat defaults are annoying

[Nuno Monteiro]

On 2005.02.07 08:47, Pozsár Balázs wrote:
> On Mon, Feb 07, 2005 at 02:48:00AM +0000, Nuno Monteiro wrote:
> >
> 
> But the contents of /proc/filesystems comes from the kernel. And the
> order of filesystems comes from the link order.
>

Yes, but /proc/filesystems is only processed after two other checks have  
failed first: specifying a filesystem type (-t), and reading /etc/ 
filesystems. Relying on mount to do the guesswork is asking for trouble  
if you realy value your data. And /etc/filesystems is the mechanism mount 
(8) has in place to change the probe order, in case you really want that.  
This is entirely a userspace problem, the kernel shouldn't have anything  
to do with it.

But, anyway, for the sake of argument let's suppose link order is  
effectively changed. You just effectively broke people's working setups,  
because like you want to rely on fs/ link order to mount your vfats as  
vfat and not as msdos, there's people out there relying on that (broken)  
assumption to have their msdos filesystems mounted as msdos. Now, with  
the new link order, they'll be mounted as vfat, and pop-goes-the-weasel.  
Tomorrow, someone unhappy that their msdos fs is now mounted as vfat will  
send a patch changing it back, thus breaking vfats. Rinse, repeat. ;-)

See? This is just wrong. This is why mount(8) has a mechanism to change  
the probe order. Everybody's happy that way, and no one has to rely on  
the broken assumption that the kernel knows how you want your filesystems  
mounted.

So, to sum things up: this is entirely an userspace problem. Yours just  
appears to be in need of fixing or tuning.



Regards,

		Nuno

Re: [PATCH] Re: msdos/vfat defaults are annoying

[Ingo Oeser]

Michelle Konzack schrieb:
> Am 2005-02-07 09:47:09, schrieb Pozsár Balázs:
> > See? I _have_ that patch applied, that's why it tried vfat and not msdos
> > first.
>
> With this, you will nerver mount a Filesystem "msdos".
>
> Because "vfat" IS "msdos" + "lfn".
>
> You can attach to ALL "msdos" media "lfn" and you will have "vfat".

So msdos is vfat WITHOUT lfn, which is a a restriction like noatime
or mounting ext3 as ext2.

That's why the default should be vfat indeed and the restriction should be
"nolfn", which will not allow lfns to be created and is what you actually 
intend, right?

But this will break API today, so it should be added to list of
features that will change.

Regards

Ingo Oeser

Re: [PATCH] Re: msdos/vfat defaults are annoying

[Horst von Brand]

Clemens Schwaighofer <cs@tequila.co.jp> said:

[...]

> but to be honest, most times I need vfat, and I actually haven't
> encountered a time when I need msdos.

But writing MSDOS on a VFAT filesystem is a sure way to screw it up, and
AFAIU vice-versa.
-- 
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Departamento de Informatica                     Fono: +56 32 654431
Universidad Tecnica Federico Santa Maria              +56 32 654239
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Re: [PATCH] Re: msdos/vfat defaults are annoying

[Clemens Schwaighofer]

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On 02/08/2005 09:23 AM, Horst von Brand wrote:
> Clemens Schwaighofer <cs@tequila.co.jp> said:
> 
> [...]
>>but to be honest, most times I need vfat, and I actually haven't
>>encountered a time when I need msdos.
> 
> But writing MSDOS on a VFAT filesystem is a sure way to screw it up, and
> AFAIU vice-versa.

well it doesn't screw it up if you write MS DOS on a VFAT, you just
loose a lot of data.

I was kinda surprised when I came home and plugged in my USB stick to
see just A3.CB instead of a nice long filename :)

- --
[ Clemens Schwaighofer                      -----=====:::::~ ]
[ TBWA\ && TEQUILA\ Japan IT Group                           ]
[                6-17-2 Ginza Chuo-ku, Tokyo 104-0061, JAPAN ]
[ Tel: +81-(0)3-3545-7703            Fax: +81-(0)3-3545-7343 ]
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Re: [PATCH] Re: msdos/vfat defaults are annoying

[H. Peter Anvin]

Followup to:  <20050207084709.GA30680@ojjektum.uhulinux.hu>
By author:    =?iso-8859-1?Q?Pozs=E1r_Bal=E1zs?= <pozsy@uhulinux.hu>
In newsgroup: linux.dev.kernel
> 
> Granted, I could override the default order by using a /etc/filesystems 
> file. But the kernel should have a much more sane default on its own, 
> namely "try vfat before msdos".
> 

What it really means is that mount(8) should know this is a special
case; presumably it already knows to try ext3 over ext2.

	-hpa