On Wed, Nov 08, 2017 at 05:06:29PM +0000, Daniel P. Berrange wrote: > On Wed, Nov 08, 2017 at 02:59:05PM -0200, Eduardo Habkost wrote: > > On Wed, Nov 08, 2017 at 01:21:33PM -0300, Philippe Mathieu-Daudé wrote: > > > On 11/08/2017 10:28 AM, Daniel P. Berrange wrote: > > > > On Mon, Oct 30, 2017 at 09:20:29AM +0100, Eduardo Habkost wrote: > > > >> On Mon, Oct 30, 2017 at 01:00:56AM -0300, Philippe Mathieu-Daudé wrote: > > > >>> examples configuring with '--enable-kvm --disable-tcg' > > > >>> > > > >>> - before > > > >>> > > > >>> $ qemu-system-x86_64 -accel help > > > >>> Possible accelerators: kvm, xen, hax, tcg > > > >>> > > > >>> $ qemu-system-x86_64 -accel tcg > > > >>> qemu-system-x86_64: -machine accel=tcg: No accelerator found > > > >>> > > > >>> # qemu-system-x86_64 -accel hax > > > >>> qemu-system-x86_64: -machine accel=hax: No accelerator found > > > >>> > > > >>> # qemu-system-x86_64 -accel xen > > > >>> xencall: error: Could not obtain handle on privileged command > > > >>> interface: No such file or directory > > > >>> xen be core: xen be core: can't open xen interface > > > >>> can't open xen interface > > > >>> qemu-system-x86_64: failed to initialize Xen: Operation not > > > >>> permitted > > > >>> > > > >>> - after > > > >>> > > > >>> $ qemu-system-x86_64 -accel help > > > >>> Possible accelerators: kvm > > > >>> > > > >>> Signed-off-by: Philippe Mathieu-Daudé <f4...@amsat.org> > > > >>> --- > > > >>> RFC because: > > > >>> - I don't think this is the nicest way, too much #ifdef'fery in > > > >>> main() > > > >> > > > >> I suggest using object_class_get_list(TYPE_ACCEL, false). > > > > > > > > And check the result of the available() method on the returned classes > > > > too, to filter the results. > > > > > > Good idea! I'll use that. > > > > It looks like QTest is the only accelerator that implements > > ->available(), and its return value is a build-time constant that > > depends only on CONFIG_POSIX. > > > > I wonder why we don't simply avoid compiling the qtest class if > > CONFIG_POSIX is unset, making the ->available() method > > unnecessary. > > Yeah that does seem simpler, though I'm surprised that Xen does not > implement the available method. Xen is an accel I'd expect to see > compiled into an x86 build, but is only available if the host is > actually booted under a Xen hypervisor. Likewise shouldn't kvm > only report itself as available if the /dev/kvm actually exists. > But maybe that's not the kind of semantics code using available() > expects ?
Currently the only caller of ->available() calls ->init_machine() immediately afterwards, so for the current code it doesn't matter if the check is inside ->available() or ->init_machine(). That said, I'm not sure we should look for /dev/kvm or check for the Xen hypervisor when handling "-accel help". I expect help text to tell the user what the QEMU binary supports, not what the current host supports. -- Eduardo
