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

[Boaz Harrosh <bharrosh@panasas.com>]

On 08/30/2011 01:34 PM, Trond Myklebust wrote:
> On Tue, 2011-08-30 at 13:24 -0700, Boaz Harrosh wrote: 
>> 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.  
> 
> ...and mode bits otherwise set to 0 so nobody can access the mounted-on
> directory.
> 
>> 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?
> 
> Yes.
> 
Nice trick. Thanks