linux-kernel - Re: [RFC PATCH] file as directory

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Message-Id: <E1HqoGh-0001kd-00@dorka.pomaz.szeredi.hu>
Date:	Wed, 23 May 2007 12:40:35 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	viro@....linux.org.uk
CC:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	akpm@...ux-foundation.org, torvalds@...ux-foundation.org
Subject: Re: [RFC PATCH] file as directory

> > Right.  After locking vfsmount_lock, mount_dironfile() should recheck
> > if there was a race and bail out.
> 
> Owww...  Not pretty, that...

If the cost of ->enter() is low, then it shouln't really be a problem.
We can't use ->i_mutex for locking, and introducing a new lock for
this doesn't sound right either.

> > I don't think the filesystem ought to try _creating_ a vfsmount.  I
> > imagine, that the fs has already a kernel-internal mounted for this
> > kind of stuff, and it just supplies a dentry from that.  The vfsmount
> > isn't actually important, but it should be readily available, and it's
> > easier to clone from a vfsmount/dentry pair.
> 
> I don't get it.  What's the point of that exercise, then?  When do you
> create that kernel-internal mount?

When the real superblock is created.  It could even be the _same_
super block as the real one.  There'd be just the problem of anchoring
the dir-on-file dentries somewhere...

Or with fuse the dir-on-file mount can just come from any mounted
filesystem, again possibly the same one as the parent.  I do actually
test with this.  The userspace filesystem supplies a file descriptor,
from which the struct path is extracted and returned from ->enter().

Miklos
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