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#xen IRC Logs for 2021-10-13

---Logopened Wed Oct 13 00:00:18 2021
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12:43<mjt>So.. who can tell me which qemu options needs to be enabled for the use of xen hvm? For a start, is it qemu-system-i386 only, or -x86_64 too? Does it need monitor frontend? block backend drivers? virtio stuff?
15:24<ChmEarl>if you are using the Xen project tarball, its only qemu-system-i386
15:34<mjt>I don't think there are other tarballs which are significantly different in this area
15:36<mjt>anyway, who does the gui part in hvm? Is it qemu or xen? And ditto for the block layer, iirc xen has its own way to define/provide block devices (and partitions?) to its domUs, not using stuff provided by qemu, right?
15:50<ChmEarl>qemu-system-i386 -vga ? -> [std|cirrus|vmware|qxl|xenfb|tcx|cg3|none]
15:50<ChmEarl>qemu handles the gui
15:51<ChmEarl>mjt when going HVM, rarely do you need to pass qemu options since Xen forms a cmdline for qemu-system-i386, which can be seen in `ps aux | grep xen`
16:14<mjt>as far as I remember there's no direct way to pass options to qemu under xen (old recommendations suggests to replace the qemu binary with a script adding options)
16:15<mjt>and in order to see it in ps output I'll need to install xen and run hvm guest somehow, which I don't know how to do :)
16:16<mjt>since I run kvm guests on all my machines I'll have to find additional hardware where this is possible
16:17<ChmEarl>oops, qemu options means runtime options or buildtime?
16:17<mjt>I asked about the build time options
16:18<ChmEarl>sorry, misunderstood
16:18<mjt>we're thinking about building a separate qemu-system-i386 binary for use by xen
16:19<mjt>the way it is right now, "regular" qemu-system-i386 depends on all xen libs and especially versioned libxenctrl, and xen depends on qemu-system-x86 which pulls lots of other stuff
16:19<ChmEarl>1 sec, I will link the tools/Makefile where qemu options are passed
16:20<mjt>oh..
16:21<ChmEarl>line 235 here: https://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=tools/Makefile;h=757a560be043604a1c566b1638235416d3aae052;hb=refs/heads/staging-4.15
16:22<mjt>heck. I haven't realized it is the xen makefile which builds qemu. I thought it is done by the packaging stuff (on debian long time ago we had qemu-xen build)
16:23<ChmEarl>I got the meson meta dump for qemu-6 if needed
16:23<mjt>I maintain qemu in debian. It is interesting we don't pass all those extra #define's when building qemu
16:24<ChmEarl>mjt++
16:24<ChmEarl>http://199.249.188.45/xen/debian/bullseye-nmu/4fx/setup/meson-q6-cfg
16:25<ChmEarl>^ meson meta for building qemu-6 in Bullseye
16:25<ChmEarl>during a xen-4.15.1 build
16:25<mjt>um? do you mean qemu is built during xen build?
16:26<ChmEarl>yes
16:26<ChmEarl>once the xen libs are in tree
16:27<ChmEarl>concurrent build of qemu-6 is not standard, I modified the build source
16:28<mjt>I wonder if it is really necessary to build qemu when we already have it packaged..
16:29<ChmEarl>mjt its not needed as long as the qemu xen depends match
16:29<mjt>it's not used iirc..
16:29<mjt>yeah, this libxenctrl.so thing
16:30<mjt>sigh. It should be a nightmare to update xen version..
16:35<mjt>we once collected symbols qemu's using from libxenctrl.so and it looked like it should be relatively easy to modify that stuff to be able to drop this dependency. but it should be done by someone who understands a bit of xen :)
16:36<mjt>okay. this is enough for me to work on for now
16:36<mjt>ChmEarl: thank you very much!
16:39<mjt>fwiw, qemu modules are enabled by the xen build, so when installing the modules should be installed too, and these are build-dependent (modules from different build wont work)
16:41<ChmEarl>mjt, build-dependent? this is news to me
16:42<ChmEarl>not surprised that I over-looked that
17:02<andyhhp>mjt: this is all a complete disaster
17:03<andyhhp>and yes - I'm slowly trying to fix things upstream by deleting stable interfaces
17:03<andyhhp>but 15y of technical debt isn't trivial to overcome
17:04<andyhhp>it absolutely should be the case that Xen can use an other distro provided qemu
17:04<andyhhp>Xen's configure has --with-system-qemu=/path/to/foo
17:05<andyhhp>but this still isn't useful for distros in general because you'd need to build that qemu with Xen enabled, which in turn depends on the unstable interfaces in Xen, and are specific to this changeset of xen.git that you happen to have built
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---Logclosed Thu Oct 14 00:00:19 2021