Re: [PATCH v5 17/21] libnvdimm: infrastructure for btt devices

Dan Williams [off-list ref] writes:

On Wed, Jun 17, 2015 at 9:47 AM, Jeff Moyer [off-list ref] wrote:

quoted

Christoph Hellwig [off-list ref] writes:

quoted

On Wed, Jun 10, 2015 at 02:46:16PM -0400, Matthew Wilcox wrote:

quoted

Don't screw up rw_page.  The point of rw_page is to read or write a page
cache page.  It can sleep, and it indicates success by using the page
flags.  Don't try and scqueeze rw_bytes into it.  If you want rw_bytes
to be a queue operation, that's one thing, but don't mess with rw_page.

Oh, I forgot about the page manipulating nature.  Yes, we'll need a different
operation in this case.

I didn't see this addressed in the new patch set.  I'm also concerned
about the layering, but I haven't put enough time into it to really make
a better suggestion.  I really dislike the idea of yet another device
stacking model in the kernel and I'm worried the code will go in, and the
sysfs interface will end up as a "user abi" and we won't be able to
change it in the future.

Dan, have you made any progress on this, or do you have plans to?

? in v6 ->rw_bytes() moved from libnvdimm local hackery to a top-level
block device operation.  Is that your concern or something else?

Hmm, I guess I was conflating two things.  I see now that you did move
the rw_bytes into the block device operations, that looks good.  I'll
table my concerns over yet another stacking model until I can say
something intelligent about it.

Cheers,
Jeff