Messages in this thread | | | Subject | Re: [PATCH RFC 2/2] vfio-ccw: support for halt/clear subchannel | From | Halil Pasic <> | Date | Fri, 8 Jun 2018 15:13:28 +0200 |
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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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