Experimental Physics and
Industrial Control System

[email protected] (Tim Mooney) · Mon, 23 Jun 1997 11:22:15 -0500

Ralph Lange wrote...

> Another NFS@vxWorks question:
> 
> 	Our (Unix) NFS server exports two disks: / and /mnt/s5
> 	There is a soft link in / that points to the other disk:
> 
> > ls -al /usr
>    1 lrwxrwxrwx   1 root     sys             7 Dec 30 12:27 usr -> /mnt/s5/
> 
> 	Our IOCs mount the server's disks using nfsMountAll():
> 
> -> nfsDevShow
> device name          file system                                       
> -----------          -----------                                       
> /                    vwhost:/                                          
> /mnt/s5              vwhost:/mnt/s5                                    
> 
> 	I create a directory that is writeable for the IOC
> 
> drwxrwxr-x   2 lange    epics        1024 Jun 23 11:50 /usr/IOC/Local/test
> 
> 	When the IOC tries to open a file using the link it gets an error
> 
> -> dbior > /usr/IOC/Local/test/test_a
> can't create output '/usr/IOC/Local/test/test_a'
>   errno = 0xd (S_errno_EACCES)
> 
> 	whereas it succeeds using the "real" directory name
> 
> -> dbior > /mnt/s5/IOC/Local/test/test_a
> value = 0 = 0x0
>.
>.
>.
> 	Has anyone any explanation for this? (I suppose this is a bug in
> the vxWorks nfsLib...)

Sort of...  Here's an excerpt from the VxWorks FAQ that addresses the
issue:

------------------------------

19.  Why can't I do ".." at top level directories or NFS mount points?

Because, again, VxWorks does not really have a "filesystem" as most people
understand it.  The top level directories are just implemented as device
driver "node", which is used to identify the ioDev associated with the
specific VxWorks "filesystem".  Since there is no underlying filesystem
layer, the story ends there.  When you're at the top of the directory
hierarchy within a given ioDev/filesytem, you simply cannot do "..".

------------------------------

20. Why do I have trouble using relative symbolic links with NFS?

See [Q: Why can't I do ".." at top level directories or NFS mount points?]
above.  This is just another problem caused by the fact that a real filesystem
does not exist for VxWorks.  NFS client implementation actually does implement
the symbolic links correctly, using lookup and readlink.  The problem is
due to the fact that, for some relative links that use ".." or whatever, that
crosses over filesystems, VxWorks cannot have underlying subsystem that will
handle file pathname to device mapping.  

Using absolute symbolic links work just fine (i.e. full path name from top).

------------------------------

Tim Mooney
Beamline Controls & Data Acquisition
Advanced Photon Source

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System