Re: [PATCH] libnvdimm: Let revalidate_disk() revalidate region read-only

[Christoph Hellwig <hch@lst.de>]

On Mon, Mar 08, 2021 at 10:54:22PM -0800, Dan Williams wrote:
> Previous kernels allowed the BLKROSET to override the disk's read-only
> status. With that situation fixed the pmem driver needs to rely on
> revalidate_disk() to clear the disk read-only status after the host
> region has been marked read-write.
> 
> Recall that when libnvdimm determines that the persistent memory has
> lost persistence (for example lack of energy to flush from DRAM to FLASH
> on an NVDIMM-N device) it marks the region read-only, but that state can
> be overridden by the user via:
> 
>    echo 0 > /sys/bus/nd/devices/regionX/read_only
> 
> ...to date there is no notification that the region has restored
> persistence, so the user override is the only recovery.

I've just resent my series to kill of ->revalidate_disk for good, so this
obvious makes me a little unhappy.  Given that ->revalidate_disk
only ends up beeing called from the same path that ->open is called,
why can't you just hook this up from the open method?

Also any reason the sysfs attribute can't just directly propagate the
information to the disk?