viro@parcelfarce.linux.theplanet.co.uk wrote:

>On Thu, Jan 08, 2004 at 08:52:31PM +0800, Ian Kent wrote:
>  
>
>>On Wed, 7 Jan 2004, H. Peter Anvin wrote:
>>
>>    
>>
>>>These are the mount traps Al Viro has been architecting.
>>>
>>>      
>>>
>>Please tell me about these.
>>
>>I have`nt seen any discussion on the implementation.
>>
>>Just a few sentences ....
>>    
>>
>
>Special vfsmount mounted somewhere; has no superblock associated with it;
>attempt to step on it triggers event; normal result of that event is to
>get a normal mount on top of it, at which point usual chaining logics
>will make sure that we don't see the trap until it's uncovered by removal
>of covering filesystem.  Trap (and everything mounted on it, etc.) can
>be removed by normal lazy umount.
>
>Basically, it's a single-point analog of autofs done entirely in VFS.
>The job of automounter is to maintain the traps and react to events.
>
>  
>
Is there any clear advantage to doing this in the VFS other than saving 
a superblock and a dentry/inode pair or two?

I remember talking to you about this, and I seem to recall that these 
mount traps would probably communicate using a struct file, so a 
trap-user would somehow receive events about when the trap was set 
off.   Will this communication model continue to work within a cloned 
namespace?  What happens if the trap-client closes the file?

-- 
Mike Waychison
Sun Microsystems, Inc.
1 (650) 352-5299 voice
1 (416) 202-8336 voice
mailto: Michael.Waychison@Sun.COM
http://www.sun.com

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