Re: [PATCH v2 1/2] file-posix: probe discard alignment on Linux block devices

[Kevin Wolf]

Am 14.04.2025 um 17:34 hat Stefan Hajnoczi geschrieben:
> On Fri, Apr 11, 2025 at 10:15:13AM +0200, Hanna Czenczek wrote:
> > On 10.04.25 20:41, Stefan Hajnoczi wrote:
> > > Populate the pdiscard_alignment block limit so the block layer is able
> > > align discard requests correctly.
> > > 
> > > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> > > ---
> > >   block/file-posix.c | 56 +++++++++++++++++++++++++++++++++++++++++++++-
> > >   1 file changed, 55 insertions(+), 1 deletion(-)
> > 
> > Ah, I didn’t know sysfs is actually fair game.  Should we not also get the
> > maximum discard length then, too?
> 
> The maximum discard length behaves differently: the Linux block layer
> splits requests according to the maximum discard length. If the guest
> submits a discard request that is too large for the host, the host block
> layer will split it and the request succeeds. That is why I didn't make
> any changes to the maximum discard length in this series.

Do we need to do something with it for SCSI passthrough? Similar to how
we expose bs->bl.max_hw_transfer/iov in the block limits VPD page?

Kevin

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