[Mtools] large capacity USB keys

[Thierry Besancon]

        Hello

I work for a university research lab and we use lots of thinclients.
A thinclient is a linux downscaled PC.  It has no fan, no hardrive
(but uses a small flash disk - 64 MB), etc.  A thinclient connects to
a XDM unix/linux server and starts a graphical session over there
(kde, gnome, whatever session manager you want).

For a long time, there has a request from users to access USB keys
from these thinclients.

I firstly used mtools with floppyd on diskless freebsd terminals
around 1997 (some poor man thinclient we can say).  I thought of
mtools + floppyd again when faced with the USB key problem on the
linux thinclient.  So I hacked floppyd to achieve that.  The hack
deals with finding the right device name of the inserted usb key for
floppyd to open on the linux thinclient.  It is a very simple mod to
the code and not a deep mod on the floppyd protocol used.  With this
hack, users access the fat32 formatted USB keys with the mtools
commands (or MToolsFM or konqueror).  (let's be clear: the context is
a one only partition fat32 formated USB key)

That has worked for the last four years and the modified mtools
package for these thinclients is largely used within French
mathematical research community (around 1500 thinclients).


Unfortunatly USB keys have grown to capacities beyond 2 Gb and with
these new very affordable USB keys my hack has stopped to work.  It is
limited to 2 GB use keys.

The problem seems to be with the internal offsets used.  It might be
quite similar to the problem exposed by Simon Large
(address@hidden) on January 2008 except that I have 8
bytes offset on my systems.

At a first glance, commands fail with 

        "Big disks not supported on this architecture."

I commented out the code and some things work (I can "mdir x:" where
x: is the remote usb key drive) but when I copy a large file (a 300MB
iso file for example) from the usb drive to the server filesystem I get
problems with llong.c:truncBytes32() complaining about too large offset.

Can someone give me a hint where to look at, please ?  I started
looking at the code but as usual, it is always uneasy to understand
someone's code when you are unfamiliar with the subject (fat
filesystems handling here).  I might debug by myself if I am given some
basic explanations about how a file is written or read back/from the
fat drive and what large capacities imply.

Thanks in advance.

Best regards,
        Thierry Besançon


_______________________________________________
Mtools mailing list
address@hidden
http://list.mtools.linux.lu/