[LSF/MM/BPF BOF] Userspace command abouts

[Hannes Reinecke]

Hi all,

it has come up in other threads, so it might be worthwhile to have its 
own topic:

Userspace command aborts

As it stands we cannot abort I/O commands from userspace.
This is hitting us when running in a virtual machine:
The VM sets a timeout when submitting a command, but that
information can't be transmitted to the VM host. The VM host
then issues a different command (with another timeout), and
again that timeout can't be transmitted to the attached devices.
So when the VM detects a timeout, it will try to issue an abort,
but that goes nowhere as the VM host has no way to abort commands
from userspace.
So in the end the VM has to wait for the command to complete, causing
stalls in the VM if the host had to undergo error recovery or something.

With io_uring or CDL we now have some mechanism which look as if they
would allow us to implement command aborts.
So this BoF will be around discussions on how aborts from userspace 
could be implemented, whether any of the above methods are suitable, or 
whether there are other ideas on how that could be done.

Cheers,

Hannes
-- 
Still without a .sig on this computer