Re: [Qemu-devel] [Qemu-block] [PATCH for-2.8] block: Let write zeroes fallback work even with small max_transfer

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Mon, Nov 14, 2016 at 09:50:33AM -0600, Eric Blake wrote:
> On 11/10/2016 02:03 AM, Kevin Wolf wrote:
> 
> >>>>> Test case:
> >>>>>
> >>>>> $ qemu-img create -f qcow2 -o cluster_size=1M file 10M
> >>>>> $ losetup /dev/loop2 /path/to/file
> >>>>> $ qemu-io -f qcow2 /dev/loop2
> >>>>> qemu-io> w 7m 1k
> >>>>> qemu-io> w -z 8003584 2093056
> >>>>
> >>>> Please include a qemu-iotests test case to protect against regressions.
> >>>
> >>> None of the existing qemu-iotests use losetup; I guess the closest thing
> >>> to do is crib from a test that uses passwordless sudo?
> >>>
> >>> It will certainly be a separate commit, but I'll give it my best shot to
> >>> post something soon.
> >>
> >> Alternatively, maybe add a blkdebug option to emulate a small max_transfer at
> >> the protocol layer?
> > 
> > This sounds like the better option indeed.
> 
> I'm working on this, but found that blkdebug doesn't yet support discard
> or write zero. While I do plan on adding that support, it is a new
> feature to blkdebug, and therefore probably belongs in 2.9.  That said,
> I'm still hoping to post an entire series with improved blkdebug and
> qemu-iotest coverage of the two tangentially related patches (this one
> for write zeroes, and another for discard support), where we can pick
> the first half of the series (basically v2 of my pending patches) into
> 2.8 while feeling more confident that the second half (the blkdebug and
> testsuite additions) wait for 2.9.

We've reached hard freeze so I like the idea of taking just small fixes
now.

Please send them for -rc0 or -rc1.

Stefan

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