On 06/08/2018 02:20 PM, Cornelia Huck wrote:
My proposal is to do the same
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).
This I do not agree scsw(r) is part of the driver.
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.
Hm, I rather consider that "we write a status, and the backend figures
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).
Regards,
Halil
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