linux-kernel - Re: [patch 6/9] fuse: add export operations

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Message-Id: <200805092002.m49K2R5p014283@agora.fsl.cs.sunysb.edu>
Date:	Fri, 9 May 2008 16:02:27 -0400
From:	Erez Zadok <ezk@...sunysb.edu>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Miklos Szeredi <miklos@...redi.hu>, akpm@...ux-foundation.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 6/9] fuse: add export operations 

In message <20080509194030.GA29118@...radead.org>, Christoph Hellwig writes:
> > +struct fuse_inode_handle
> > +{
> > +	u64 nodeid;
> > +	u32 generation;
> > +};
> 
> This is the same filehandle type XFS uses for 64bit inode filesystems
> where the parent is not encoded.  I'll post a patch soon to move that
> 64bit inode handling to common code.  I don't think it's a good idea
> to delay your patch until that happens, but can you chose the fid
> types to be the same as XFS does currently so that a conversion is
> easily possible.  The fh_type should be 0x81 (fh type 1 order by 0x80
> to imply it's 64bit inodes)
> 
> In case you want to look at that patch I'v uploaded the current
> version at http://verein.lst.de/~hch/generic-64bit-inode-export
> 
> > +static struct dentry *fuse_get_dentry(struct super_block *sb,
> > +				      struct fuse_inode_handle *handle)
> > +{
> > +	struct inode *inode;
> > +	struct dentry *entry;
> > +	int err = -ESTALE;
> > +
> > +	if (handle->nodeid == 0)
> > +		goto out_err;
> > +
> > +	inode = ilookup5(sb, handle->nodeid, fuse_inode_eq, &handle->nodeid);
> > +	if (!inode)
> > +		goto out_err;
> 
> Only finding in-memory inodes for nfs export is quite dangerous.  I
> think it would be a much better idea to support whatever upcalls are
> needed to find the object if it's not in memory.  Without that the nfs
> exporting support is hardly useable.

In the ODF version of unionfs, we store the inode numbers persistently in a
small /odf partition, exactly for that reason.  It'd be wonderful if there
was kernel support for persistent inode numbers that could be used by
various virtual filesystems.

Erez.
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