USB Key and modules


I am using a 11.2.
When I plug my USB Key, and I mount it, everything works fine.

I see that some additional modules are automatically loaded when I make the mount :
fat, vfat, nls_cp437 & nls_iso8859_1

I also have a custom install (using a boot PXE and a nfs root system)
Kernel and modules are the same as on my 11.2
When I try to mount the key, it fails. (unknown filesystem type vfat)

If I manually load the modules (fat, vfat, nls_cp437 & nls_iso8859_1) it works.

I would like to have the same behaviour on both machines (automatic load of modules), but I don’t understand how this is done…

Who manages the load of the missing modules (additional process or additionnal module) ?
Or is there something missing in my custom install ?

I tried strace on the execution of the mount, but didn’t find any clue.

when it works :
stat64("/sbin/mount.vfat", 0xbfb546f8) = -1 ENOENT (No such file or directory)
mount("/dev/sdb1", “/mnt”, “vfat”, MS_MGC_VAL, NULL) = 0

when if fails:
stat64("/sbin/mount.vfat", 0xbfc86888) = -1 ENOENT (No such file or directory)
mount("/dev/sdb1", “/mnt”, “vfat”, MS_MGC_VAL, NULL) = -1 ENODEV (No such device)

So it seems that the only difference is that the execution of the mount function fails in the second case.
But, in the working case, I didn’t find any line dealing with automatical load of modules…