Re: [PATCH v4] block: create ioctl to discard-or-zeroout a range of blocks

[Christoph Hellwig <hch@infradead.org>]

On Fri, Nov 13, 2015 at 02:01:43PM -0800, Darrick J. Wong wrote:
> Create a new ioctl to expose the block layer's newfound ability to
> issue either a zeroing discard, a WRITE SAME with a zero page, or a
> regular write with the zero page.  This BLKZEROOUT2 ioctl takes
> {start, length, flags} as parameters.  So far, the only flag available
> is to enable the zeroing discard part -- without it, the call invokes
> the old BLKZEROOUT behavior.  start and length have the same meaning
> as in BLKZEROOUT.
> 
> Furthermore, because BLKZEROOUT2 issues commands directly to the
> storage device, we must invalidate the page cache (as a regular
> O_DIRECT write would do) to avoid returning stale cache contents at a
> later time.

So does BLKZEROOUT.  Seems like adding the cache invalidation should
be one patch and the ioctl another one.  Otherwise this looks fine
except that I kinda hate BLKZEROOUT2 name, but can't come up with
anything better.