arm has no default machine type

[Dan Streetman]

[impact]

The qemu-system-* binaries for most archs have a default machine type, meaning no --machine needs to be specified. This is extremely useful for situations running qemu on multiple archs in a common way, for example what systemd's self-testing does.

On arm archs, there is no default, so --machine must be specified. It would be better (i.e. qemu users would not need to include arch-specific qemu parameters) if there was a default machine for arm.

[test case]

install qemu-system-arm, and try to run qemu without any --machine specified.

Also, this command will show if there isn't any default machine defined (unless fixed):

$ qemu-system-aarch64 -M ? | grep default

[regression potential]

since no default is currently defined, all users of qemu-system-aarch64 or qemu-system-arm must currently define a machine type. This change would (should) not have any effect on them, since it only sets a default machine type for use when -M is not specified.

[other info]

I'm preparing a patch to send upstream and will add the link once sent.

[Dan Streetman (ddstreet)]

I've targeted this to b/d/e, but it's not a bug fix, so no guarantee. It should be really simple though, and IMHO quite useful, so maybe cpaelzer can let it ride along with some other qemu sru.

Depends on getting it upstream first, of course.

[Dan Streetman (ddstreet)]

patch sent upstream:
https://lists.nongnu.org/archive/html/qemu-devel/2019-09/msg03627.html

also this change is related to the systemd upstream PR here:
https://github.com/systemd/systemd/pull/13409

because arm is the only testbed arch where a machine type needs to be specified.

[Christian Ehrhardt  (paelzer)]

I agree to the low regression potential of this as anyone using a cmdline that would be affected today gets an immediate failure by a missing type. So I'm fine to consider adding this along some other SRU.

But I'd only do so if upstream qemu-arm can agree on it, thanks for sending it there already.

[Christian Ehrhardt  (paelzer)]

FYI - not accepted yet and discussion seems to be stuck. Upstream almost seems to prefer to drop default types everyhere ...

[Dan Streetman (ddstreet)]

I just sent a follow up email to try to revive, or at least wrap up, discussion upstream.

[Dan Streetman (ddstreet)]

Looks like this isn't going anywhere upstream, unfortunately; if anything, it seems like there's more interest in *removing* default machine types for other archs, instead of adding a default machine type for arm.

@paelzer unless you think there's value in Ubuntu carrying a patch to add an arm default machine type, I think we can close this bug as wontfix.

[Christian Ehrhardt  (paelzer)]

Ack to the summary in the last comment, thanks for trying ddstreet.
Closing the bug.