Hi Markus, (+Michal, Peter)
On 03/11/19 23:08, Markus Armbruster wrote: > The PC machines put firmware in ROM by default. To get it put into > flash memory (required by OVMF), you have to use -drive > if=pflash,unit=0,... and optionally -drive if=pflash,unit=1,... > > Why two -drive? This permits setting up one part of the flash memory > read-only, and the other part read/write. It also makes upgrading > firmware on the host easier. Below the hood, it creates two separate > flash devices, because we were too lazy to improve our flash device > models to support sector protection. > > The problem at hand is to do the same with -blockdev somehow, as one > more step towards deprecating -drive. > > Mapping -drive if=none,... to -blockdev is a solved problem. With > if=T other than if=none, -drive additionally configures a block device > frontend. For non-onboard devices, that part maps to -device. Also a > solved problem. For onboard devices such as PC flash memory, we have > an unsolved problem. > > This is actually an instance of a wider problem: our general device > configuration interface doesn't cover onboard devices. Instead, we have > a zoo of ad hoc interfaces that are much more limited. One of them is > -drive, which we'd rather deprecate, but can't until we have suitable > replacements for all its uses. > > Sadly, I can't attack the wider problem today. So back to the narrow > problem. > > My first idea was to reduce it to its solved buddy by using pluggable > instead of onboard devices for the flash memory. Workable, but it > requires some extra smarts in firmware descriptors and libvirt. Paolo > had an idea that is simpler for libvirt: keep the devices onboard, and > add machine properties for their block backends. > > The implementation is less than straightforward, I'm afraid. > > First, block backend properties are *qdev* properties. Machines can't > have those, as they're not devices. I could duplicate these qdev > properties as QOM properties, but I hate that. > > More seriously, the properties do not belong to the machine, they > belong to the onboard flash devices. Adding them to the machine would > then require bad magic to somehow transfer them to the flash devices. > Fortunately, QOM provides the means to handle exactly this case: add > alias properties to the machine that forward to the onboard devices' > properties. > > Properties need to be created in .instance_init() methods. For PC > machines, that's pc_machine_initfn(). To make alias properties work, > we need to create the onboard flash devices there, too. Requires > several bug fixes, in the previous commits. We also have to realize > the devices. More on that below. > > If the user sets pflash0, firmware resides in flash memory. > pc_system_firmware_init() maps and realizes the flash devices. > > Else, firmware resides in ROM. The onboard flash devices aren't used > then. pc_system_firmware_init() destroys them unrealized, along with > the alias properties. > > The existing code to pick up drives defined with -drive if=pflash is > replaced by code to desugar into the machine properties. > > Signed-off-by: Markus Armbruster <arm...@redhat.com> > Reviewed-by: Philippe Mathieu-Daudé <phi...@redhat.com> > Acked-by: Laszlo Ersek <ler...@redhat.com> > Reviewed-by: Michael S. Tsirkin <m...@redhat.com> > Message-Id: <87ftrtux81....@dusky.pond.sub.org> > --- > hw/i386/pc.c | 2 + > hw/i386/pc_sysfw.c | 233 ++++++++++++++++++++++++++++--------------- > include/hw/i386/pc.h | 3 + > 3 files changed, 156 insertions(+), 82 deletions(-) the next patch in the series -- which is now commit e33763be7cd3 -- updates the command line recommendation regardless of system emulation target / machine type. But, the series (i.e., this patch, ultimately) implements support for the new command line only for the PC machine types. I think the same interface should be implemented for (arm|aarch64)/virt too, because those machine types are covered by "docs/interop/firmware.json" similarly, and once Michal does the libvirt work for "pflash via -blockdev", libvirt will want to use uniform cmdline options for both sets of machine types. (Search "hw/arm/virt.c" for IF_PFLASH / create_one_flash().) ... Yes, this omission is in fact "reviewer fail" (if you allow me to steal that term); I should have noticed this *much* earlier. I've only realized now, from <https://lists.gnu.org/archive/html/qemu-devel/2019-03/msg07070.html>. Mea culpa :( (It's just as well that this is not a "correctness" but "completeness" kind of problem -- whatever has been committed thus far should be OK.) Thanks, Laszlo