linux-kernel - Re: [PATCH 12/13] sysfs: Propagate renames to the vfs on demand

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Message-Id: <E1N6jDk-0006eq-23@pomaz-ex.szeredi.hu>
Date:	Sat, 07 Nov 2009 12:12:40 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	ebiederm@...ssion.com (Eric W. Biederman)
CC:	tj@...nel.org, serue@...ibm.com, gregkh@...e.de,
	kay.sievers@...y.org, greg@...ah.com, linux-kernel@...r.kernel.org,
	cornelia.huck@...ibm.com, linux-fsdevel@...r.kernel.org,
	eric.dumazet@...il.com, bcrl@...et.ca, ebiederm@...stanetworks.com
Subject: Re: [PATCH 12/13] sysfs: Propagate renames to the vfs on demand

On Fri, 06 Nov 2009, ebiederm@...ssion.com (Eric W. Biederman wrote:
> Tejun Heo <tj@...nel.org> writes:
> 
> > Hello,
> >
> > Eric W. Biederman wrote:
> >> It isn't what I want but it is what the VFS requires.  If let the vfs
> >> continue on it's delusional state we will leak the vfs mount and
> >> everything mounted on top of it, with no way to remove the mounts.

"umount -l" on the whole thing will clear any submounts up too.

> >
> > This is caused by not having any way to prevent deletion on
> > directories with submounts, right?  How does other distributed
> > filesystems deal with directories with submounts going away underneath
> > it?
> 
> NFS does exactly the same thing I am doing.

Yes, this is a problem for NFS too.  You cannot tell the NFS server
"this directory is mounted on some client, don't let anything happen
to it!".  Basically the remaining choices are:

 a) let the old path leading up to the mount still be accessible, even
 though it doesn't exist anymore on the server (or has been replaced
 with something different)

 b) automatically dissolve any submounts if the path disappeard on the
 server

I think Al was arguing in favor of b), while Linus said that mounts
must never just disappear, so a) is better.  I don't think an
agreement was reached.

Thanks,
Miklos
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