Re: [Qemu-devel] [Qemu-block] [PATCH for-3.0] file-posix: Fix write_zeroes with unmap on block devices

[Nir Soffer]

On Thu, Jul 26, 2018 at 5:28 PM Eric Blake <address@hidden> wrote:

> On 07/26/2018 06:33 AM, Kevin Wolf wrote:
> > The BLKDISCARD ioctl doesn't guarantee that the discarded blocks read as
> > all-zero afterwards, so don't try to abuse it for zero writing. We try
> > to only use this if BLKDISCARDZEROES tells us that it is safe, but this
> > is unreliable on older kernels and a constant 0 in newer kernels. In
>
> For my own curiosity, which kernel commit switched to constant 0, so I
> can read the rationale in that commit message?
>

This should help
https://patchwork.kernel.org/patch/9903757/

Nir