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SubjectRe: [PATCH 1/3] vfs: merge .d_select_inode() into .d_real()
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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


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