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Date: Fri, 19 Aug 2005 17:53:32 +0100
From: Al Viro <viro@parcelfarce.linux.theplanet.co.uk>
To: Linus Torvalds <torvalds@osdl.org>
Cc: Anton Altaparmakov <aia21@cam.ac.uk>, vandrove@vc.cvut.cz,
       Andrew Morton <akpm@osdl.org>, linware@sh.cvut.cz,
       fsdevel <linux-fsdevel@vger.kernel.org>,
       lkml <linux-kernel@vger.kernel.org>
Subject: Re: Kernel bug: Bad page state: related to generic symlink code and mmap
Message-ID: <20050819165332.GD29811@parcelfarce.linux.theplanet.co.uk>
References: <1124450088.2294.31.camel@imp.csi.cam.ac.uk> <20050819142025.GA29811@parcelfarce.linux.theplanet.co.uk> <1124466246.2294.65.camel@imp.csi.cam.ac.uk> <Pine.LNX.4.58.0508190855350.3412@g5.osdl.org> <Pine.LNX.4.58.0508190913570.3412@g5.osdl.org> <Pine.LNX.4.58.0508190934470.3412@g5.osdl.org>
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On Fri, Aug 19, 2005 at 09:43:17AM -0700, Linus Torvalds wrote:
> Actually, looking at the ncpfs patch, I'd rather not apply that patch 
> as-is. It looks like it will totally disable symlink caching, which would 
> be kind of sad. Somebody willing to do the same thing NFS does?
> 
> NFS hides away the "struct page *" pointer at the end of the page data, so
> that when we pass the pointer to the virtual address around, we can 
> trivially look up the "struct page".
> 
> An alternative is to make the symlink address-space use a gfp_mask of 
> GFP_KERNEL (no highmem), at which point ncpfs_put_link() just becomes 
> something like
> 
> 	void ncpfs_put_link(struct dentry *dentry, struct nameidata *nd)
> 	{
> 		char *addr = nd_get_link(nd);
> 
> 		if (!IS_ERR(addr))
> 			page_cache_release(virt_to_page(addr));
> 	}
> 
> which is pretty ugly, but even simpler than the NFS trick.
> 
> Anybody?

I'm taking NFS helpers to libfs.c and switching ncpfs to them.  IMO that's
better than copying the damn thing and other network filesystems might have
the same needs eventually...