Filesystem module autoprobe?

Filesystem module autoprobe?

[Phillip Susi]

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I thought that these days module autoprobe was pretty much taken care
of and that in the case of filesystems, an attempt to mount a
filesystem for which a module had not yet been loaded would result in
the kernel forking a modprobe on fs-xxx, which would use the module
aliases to match up an appropriate module and load it.  So why is it
that when I try to mount an ext2 filesystem mount complains that
there's no such filesystem until I modprobe ext2?

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Re: Filesystem module autoprobe?

[James Bottomley]

On Mon, 2013-12-23 at 22:34 -0500, Phillip Susi wrote:
> I thought that these days module autoprobe was pretty much taken care
> of and that in the case of filesystems, an attempt to mount a
> filesystem for which a module had not yet been loaded would result in
> the kernel forking a modprobe on fs-xxx, which would use the module
> aliases to match up an appropriate module and load it.  So why is it
> that when I try to mount an ext2 filesystem mount complains that
> there's no such filesystem until I modprobe ext2?

If you're expecting

mount /dev/sda1 /mnt

to insert all the available filesystem modules and discover
that /dev/sda1 is ext2, this is a case of mismatched user expectations
(because we won't).

If

mount -t ext2 /dev/sda1 /mnt

isn't autoprobing, that's either a bug or a distribution problem.

James

Re: Filesystem module autoprobe?

[Phillip Susi]

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On 12/24/2013 03:22 PM, James Bottomley wrote:
> If you're expecting
> 
> mount /dev/sda1 /mnt
> 
> to insert all the available filesystem modules and discover that
> /dev/sda1 is ext2, this is a case of mismatched user expectations 
> (because we won't).

mount uses libblkid to identify the correct filesystem and tells the
kernel to use it.

> If
> 
> mount -t ext2 /dev/sda1 /mnt
> 
> isn't autoprobing, that's either a bug or a distribution problem.

So that *should* autoprobe?  Any pointers to some docs on how that is
supposed to work or where to start looking to figure out why it isn't?


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Re: Filesystem module autoprobe?

[James Bottomley]

On Tue, 2013-12-24 at 16:31 -0500, Phillip Susi wrote:
> On 12/24/2013 03:22 PM, James Bottomley wrote:
> > If you're expecting
> > 
> > mount /dev/sda1 /mnt
> > 
> > to insert all the available filesystem modules and discover that
> > /dev/sda1 is ext2, this is a case of mismatched user expectations 
> > (because we won't).
> 
> mount uses libblkid to identify the correct filesystem and tells the
> kernel to use it.

No idea about that, but making it work is a distro specific problem, I'd
look at the source code.  However, if you pass a NULL fstype to
sys_mount, it will try every fs it knows about until one says yes.

> > If
> > 
> > mount -t ext2 /dev/sda1 /mnt
> > 
> > isn't autoprobing, that's either a bug or a distribution problem.
> 
> So that *should* autoprobe?  Any pointers to some docs on how that is
> supposed to work or where to start looking to figure out why it isn't?

Yes, mount -t <fstype>  should try to load a module with alias
fs-<fstype> each filesystem module has a MODULE_ALIAS_FS which
constructs this.

James