inode_operations's lookup question

[mohanlal jangir <mohanlal@xxxxxxxxxxx>]

I was experimenting with the tutorial and code available at 
www.geocities.com/ravikiran_uvs/articles/rkfs.html

Attached code is a subset of that available at abovementioned link. 
Following are the observations, if I compile the code without defining macro 
HAVE_LOOKUP_FUNCTION

#mount -t rkfs none /mnt/cdrom
<rkfs_get_sb> invoked
<rkfs_super_read_inode> invoked
#file /mnt/cdrom
/mnt/cdrom/: can't stat `/mnt/cdrom/' (Not a directory)

If I compile the code with HAVE_LOOKUP_FUNCTION defined, following are the 
observations

#mount -t rkfs none /mnt/cdrom
<rkfs_get_sb> invoked
<rkfs_super_read_inode> invoked
#file /mnt/cdrom
/mnt/cdrom/: directory

but the function rkfs_inode_lookup is NOT invoked. How come kernel is able 
to differentiate without calling this function? Does it simply check if the 
member lookup is non-null? Which file the kernel code for this is defined 
in?

Regards,
Mohanlal

Attachment: rkfs.c
Description: Binary data