linux-kernel - Re: [PATCH 07/25] r/o bind mounts: elevate write count for some ioctls

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Date:	Fri, 21 Sep 2007 01:17:06 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Dave Hansen <haveblue@...ibm.com>
Cc:	linux-kernel@...r.kernel.org, hch@...radead.org
Subject: Re: [PATCH 07/25] r/o bind mounts: elevate write count for some
 ioctls

On Thu, 20 Sep 2007 12:52:57 -0700 Dave Hansen <haveblue@...ibm.com> wrote:

> +		ret = mnt_want_write(filp->f_vfsmnt);

It still creeps me out that we have this sprinkled *all over* the tree and
people will forget to do it and there's no runtime or compile-time checking
that they remembered to do it and when they forget to do it nobody will
notice that it broke until ages and ages later.

IOW: it is a sheer horror for maintainability.

Please have a think about what we can do about this.  For example, if you'd
thought about this up-front, (and I think it's a big problem), we could
have done something grotty like, in mnt_want_write():

	current->vfsmnt_im_allowed_to_write_to = inode;

and then check that current->vfsmnt_im_allowed_to_write_to is the correct
inode in __mark_inode_dirty() and various other strategic places.  That
sort of thing.

We need to do *something*, I think.  This code just doesn't look feasibly
maintainable to me.

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