Re: dm thin metadata: clarify __open_device functionality and fix callers

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On Tue, Jan 10 2012 at  5:31am -0500,
Joe Thornber <thornber@xxxxxxxxxx> wrote:

> On Mon, Jan 09, 2012 at 03:33:08PM -0500, Mike Snitzer wrote:
> > The __open_device() error path of __create_thin() and __create_snap()
> > will call __close_device() even if td was not initialized by
> > __open_device().
> >
> > Clearly define what callers should expect from __open_device()'s
> > return.
> >
> > Also, remove redundant 'td->changed = 1' in __create_thin() --
> > __open_device() with create=1 will have set td->changed on successful
> > return.
> 
> Hi Mike,
> 
> This looks like a code review patch, and as such I ACK it.

Yes, this was something that Alasdair came across when he inspected the
error path of __create_thin().  He was looking at this because Kabi was
having issues with opencount on a DM device (device held open when he
wasn't aware of any openers).
 
> I don't think it changes any behaviour though.  Both create_thin and
> create_snapshot hold a mutex when they run, and the first thing they
> do is check for the existence of the device.
> 
>         r = dm_btree_lookup(&pmd->details_info, pmd->details_root,
>                             &key, &details_le);
>         if (!r)
>                 return -EEXIST;
> 
> I don't think there's a race on creation?

Right, doesn't change any behavior -- other than fix the error path to
not decrement some random memory (uninitialized @td) in
__close_device().

(and no I wasn't suggesting there was some race on creation).

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