I just noticed in initramfs that i can't rmmod xen-blkfront and modprobe
it again :
it will says something like the device major allready exists and indeed
the line about xvd stays in /proc/devices
With the dm_mod ,for example, the line disappear from /proc/modules with
maybe somthing like :
should be added to the xlblk_exit function ?
( Allthought i 'm not sure it will make any problem except for me :)