Re: [PATCH] NFSD: Add a cache for fs_locations information

[Boaz Harrosh <bharrosh@panasas.com>]

On 08/30/2011 01:00 PM, Chuck Lever wrote:
<>
>> 
>> Won't the above check be rather expensive? You'll need to do a 
>> getxattr call on almost every path component of every lookup,
>> right?
>> 
>> I may be misremembering your talk from connectathon, but I thought
>> you were planning to use a well-known mode for junctions that would
>> cut down on the number of unnecessary getxattrs...
> 
> Yes, that's the plan.  To reduce overhead, the S_ISVTX bit must be
> set before NFSD does the expensive xattr test.  

from: stat(2) - Linux man page

The 'sticky' bit (S_ISVTX) on a directory means that a file in that
directory can be renamed or deleted only by the owner of the file, 
by the owner of the directory, and by a privileged process.

Please explain how does it work? Once the junction is followed and
mounted then the mode-bits get changed to the destination directory's
mode bits? So the Server's junction mode-bits are never exposed, except
in a local-fs file access on the server?

Thanks
Boaz

> However, I don't
> think this kind of filtering was ever implemented.  I got the patch
> from here:
> 
> http://git.linux-nfs.org/?p=trondmy/nfs-2.6.git;a=shortlog;h=refs/heads/fedfs-for-2.6.34
>
>  and that doesn't seem to have it either.  I can implement something
> and repost these.
>