- Intorduce and use a message type for VFS_GETDENTS, VFS_READ,
VFS_WRITE.
- Some cleanup to related functions where vir_bytes are replaced (and
casted to/from, in parameter definition and local variables as well.
This allow to see more clearly which function receives unsafe
(pointer) values, or at least values which are not supposed to be
valid in the address space of VFS. The current patch does so only
for the minimal amount of functions which are concerned with the
introduction of the new message type.