Re: [RFC] mount can figure out fstype automatically

Craig Rodrigues wrote:
> On Sat, Jul 08, 2006 at 09:05:51AM -0700, Sam Leffler wrote:
>> Linux has -t auto; haven't looked at how it works.
> 
> I didn't want to implement -t auto, in
> case that would confuse things in case someone gets around
> to implementing autofs for FreeBSD, so I just used -t "".

Oh, I stupidly assumed "auto" meant something similar to what you were
doing :)

> 
>> It appears you just try a series of fs types; can't you read the device
>> to infer the filesystem?
> 
> I was thinking of doing something like that.  You can basically
> get the same info by doing something like:
> 
> file - < /dev/ad0s1e
> /dev/stdin: Unix Fast File system (little-endian)
> 
> file - < /dev/ad0s4
> /dev/stdin: SGI XFS filesystem
> 
> 
> I leaned away from this approach in mount(8) because:
> - I didn't want to tie mount(8) to file(1)
> - I didn't want to build up a table of known superblocks
>   inside mount(8) because every time a new filesystem is
>   added to FreeBSD, mount(8) would need to be updated
> 
> If there was a way, maybe at the GEOM or filesystem level to
> "taste" what type of filesystem existed on a device, and/or
> have a filesystem advertise what type of superblock it has,
> then that would be a nice way to do it, but I couldn't figure
> out a way to easily do it.

I wouldn't expect a program like mount to fork+exec file; I'd expect it
to either read directly or use a kernel facility.  Sounds like something
is missing to do this right.

	Sam