linux-kernel - Re: [PATCH 1/3] vfs: merge .d_select_inode() into .d

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Date:	Sun, 22 May 2016 09:39:33 -0700
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Miklos Szeredi <miklos@...redi.hu>,
	Al Viro <viro@...IV.linux.org.uk>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	David Howells <dhowells@...hat.com>
Subject: Re: [PATCH 1/3] vfs: merge .d_select_inode() into .d_real()

On Tue, 2016-05-17 at 23:53 +0200, Miklos Szeredi wrote:
> The two methods essentially do the same: find the real dentry/inode
> belonging to an overlay dentry.  The difference is in the usage:
> 
> vfs_open() uses ->d_select_inode() and expects the function to 
> perform copy-up if necessary based on the open flags argument.
> 
> file_dentry() uses ->d_real() passing in the overlay dentry as well 
> as the underlying inode.
> 
> vfs_rename() uses ->d_select_inode() but passes zero flags.  
> ->d_real() with a zero inode would have worked just as well here.
> 
> This patch merges the functionality of ->d_select_inode() into 
> ->d_real() by adding an 'open_flags' argument to the latter.

Actually, before you do this, I have a use case for keeping them
separate:  The shiftfs prototype I've posted cannot use d_select_inode
because it's shifting the uid/gids, so the inode permissions have to be
done on the upper inode.  However, several filesystems make use of
file_dentry() and for them, I need to supply the lower dentry, so I end
up setting d_real but not d_select_inode.

for me, then vfs_open and vfs_rename have to operate on the upper inode
but all uses of file_dentry should return the lower dentry.

James