Re: [PATCH 1/3 v2.1] btrfs: write_dev_flush does not return ENOMEM anymore

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On Wed, Jun 14, 2017 at 05:01:11PM +0800, Anand Jain wrote:
> > I have a prototype for the
> > preallocated flush bio but was waiting until these cleanups are in
> > before snding it.
> 
>   oh. sorry for the delay if any. -ENOMEM was only purpose I had/have
>   in mind for peralloc, but looks like there is another purpose which
>   I am not aware of.

The bio preallocation is a slight optimization, we don't have to
allocate and free the bio all the time.

> > I've noticed that threre are two more "if (!device->bdev)" checks under
> > the device lock in write_all_supers, that might be worth removing.
> 
> > However, a NULL bdev and device->missing are related and I think there
> > are some dark corners in dev replace where the invariant can be
> > temporarily broken.
> 
>   Ok. Thanks for the hints. Trying to dig.
> 
> > Given that we probably don't have great testing
> > coverage of devices with the flush capabilities,
> 
>   Any hints on what type of test coverage ?

Devices used for normal testing, any sort of test basically, that do not
have the flush capabilities will never exercise the in write_dev_flush.
So any reference counts or failures will not get covered.
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