On Fri, 8 Jun 2018 15:13:28 +0200
Halil Pasic <pasic@xxxxxxxxxxxxx> wrote:
On 06/08/2018 02:20 PM, Cornelia Huck wrote:
Hm, I rather consider that "we write a status, and the backend figuresMy proposal is to do the sameThis I do not agree scsw(r) is part of the driver.
copying to scsw(r) again, which would mean we get a request with both
the halt and the start bit set. The vfio code now needs to do a hsch
(instead of a ssch). The real channel subsystem should figure this out,
as we can't reliably check whether the start function has concluded
already (there's always a race window).
The interface here is not a device interface anymore but a driver
interface.
SCSW is a status, it is at its place in QEMU device interface with the
guest
but here pwrite() sends a command.
out what to do based on that status".
The status of what? Kind of a target status?
I think this approach is the source of lots of complications. For instance
take xsch. How are we supposed to react to a guest xsch (in QEMU and
in the kernel module)? My guess is that the right thing to do is to issue
an xsch in the vfio-ccw kernel module on the passed through subchannel.
But there is no bit in fctl for cancel.
Bottom line is: I'm not happy with the current design but I'm not sure
if it's practical to do something about it (i.e. change it radically).
It might make sense to keep this for ssch, maybe reuse it for hsch/csch,
and think about something else for other things we want to handle
(xsch, channel monitoring, the path handling stuff for which we already
had a prototype etc.) It's probably not practical to do radical surgery
on the existing code.
[Speaking of which: Is there any current effort on the path handling
things?]