Re: [patch 00/13] vfs: add helpers to check r/o bind mounts

[Dave Hansen <dave@linux.vnet.ibm.com>]

On Thu, 2008-04-24 at 17:37 +0200, Miklos Szeredi wrote:
> Why are those so important?  Yes, if we have multiple vfs_() calls,
> surround them with an extra want/drop pair.  We do already do multiple
> overlapping want/drop pairs with O_TRUNC and O_CREAT (AFAIR).

The one that I remember is the pair that we take for O_CREAT and the
nameidata_to_filp() in do_filp_open() that we do on it after the
creation and hold while the file is open.

The only reason for this one is that we want to shut down a potential
race that would allow the file to be created, then still return a -EROFS
because someone did a r/w->r/o transition between the create an the
nameidata_to_filp().

We could pass some information into nameidata_to_filp()->__dentry_open()
telling it that we already have a write and it doesn't need to take one,
but I think having the two nested writes is cleaner.

Is that the case you're thinking of?

-- Dave