linux-kernel - RE: encode_fh: have inode but no dentry

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Message-ID: <b787274a-de5f-4a0d-957e-d5a9c2f2d752@default>
Date:	Thu, 24 Feb 2011 13:51:03 -0800 (PST)
From:	Dan Magenheimer <dan.magenheimer@...cle.com>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	aneesh.kumar@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org
Subject: RE: encode_fh: have inode but no dentry

> From: Al Viro [mailto:viro@...IV.linux.org.uk]
> Subject: Re: encode_fh: have inode but no dentry
> 
> On Thu, Feb 24, 2011 at 01:16:34PM -0800, Dan Magenheimer wrote:
> > Hi Aneesh --
> >
> > I see you are continuing with encode_fh related
> > development so I thought I would bring this up
> > with you.
> >
> > I have a need to call the encode_fh op in a
> > situation where I have an inode but not a dentry,
> > and calling d_find_alias(inode) sometimes returns
> > NULL.  In my usage, connectable is always zero, so
> > having just the inode should be sufficient to get
> > useful results from encode_fh, at least for the
> > filesystems I've looked at.
> 
> [snip]
> 
> > Such a change would require a patch that touched
> > nearly every filesystem so it's clearly not to
> > be taken lightly.
> >
> > Any thoughts on this?
> 
> How about "tell us what do you need that for", for starters?

(Wow, that was fast! /me pictures a 64-core Al Viro
parallelizing incoming lkml email.)

It's for some work I'm building on top of cleancache.
Since cleancache isn't merged (yet), it's not pressing,
but this seemed a reasonable approach so, before I
started looking at more complicated alternatives,
I thought I'd get some idea if this is feasible or not.

The situation arises when the inode is in cache but
the dentry is not, but I still need a filehandle.
In the non-connectable case, this should still be OK.
Seems like a case that might be more broadly useful.

Thanks,
Dan
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