why there is a complex sync between /var/lib/nfs/etab in user-mode and export_table in kernel mode?

["lioupayphone" <lioupayphone@gmail.com>]

Hello, linux-nfs

i found that an entry in /var/lib/nfs/etab (etab for abbr)  was written to exprot_table of kernel-mode via a proc-file when a client requests mnt this entry.                                       
when the entry in export_table of kernel-mode was expired (eg : reached its expiration time), an upcall machanism is able to make sure that the newly entry from etab of user-mode was written to export_table of kernel-mode. ie, the entry in export_table of kernel-mode was updated by the one of user-mode.

if the content listed above is true, i think linux nfs is too complex. and why not remove the etab from user-mode?
in a word, i think it is easy to just maintain export_table of kernel-mode. we can directly scan /etc/exports and make up a complete export-entry, then write it to the export_table of kernel-mode. the entries in export_table of kernel-mode would never be expired unless we explicitly remove it from the export_table of kernel-mode (a proc MUST be provided for meeting this requirement).

when the server is rebooted and nfsd proc-filesystem is ready, just re-do "scanning the /etc/exports and make up complete export-entries, then write them into export_table of kernel-mode".  

i aims to 1) remove the complex upcall machanism ,  2) get rid of the couple of /var/lib/nfs/etab in user-mode and export_table in kernel-mode.

anyone can give me some suggestions? or points out what's wrong i am.
thank you!
 				
Best Regards! 
lioupayphone