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Re: [Qemu-block] [PATCH v2 11/12] pc: Support firmware configuration wit
Re: [Qemu-block] [PATCH v2 11/12] pc: Support firmware configuration with -blockdev
Fri, 8 Mar 2019 09:22:16 +0100
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1
On 03/07/19 18:24, 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. 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. Some of
> them we'd rather deprecate (-drive, -net), but can't until we have
> suitable replacements.
> Sadly, I can't attack the wider problem today. So back to the narrow
> 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 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 <address@hidden>
> Reviewed-by: Philippe Mathieu-Daudé <address@hidden>
> Signed-off-by: Philippe Mathieu-Daudé <address@hidden>
> hw/i386/pc.c | 2 +
> hw/i386/pc_sysfw.c | 243 ++++++++++++++++++++++++++++---------------
> include/hw/i386/pc.h | 3 +
> 3 files changed, 166 insertions(+), 82 deletions(-)
Thanks for addressing my comments!
Acked-by: Laszlo Ersek <address@hidden>
- [Qemu-block] [PATCH v2 04/12] sysbus: Fix latent bug with onboard devices, (continued)
- [Qemu-block] [PATCH v2 11/12] pc: Support firmware configuration with -blockdev, Markus Armbruster, 2019/03/07
- [Qemu-block] [PATCH v2 08/12] pflash_cfi01: Add pflash_cfi01_get_blk() helper, Markus Armbruster, 2019/03/07
- [Qemu-block] [PATCH v2 09/12] pc_sysfw: Remove unused PcSysFwDevice, Markus Armbruster, 2019/03/07
- [Qemu-block] [PATCH v2 12/12] docs/interop/firmware.json: Prefer -machine to if=pflash, Markus Armbruster, 2019/03/07
- [Qemu-block] [PATCH v2 10/12] pc_sysfw: Pass PCMachineState to pc_system_firmware_init(), Markus Armbruster, 2019/03/07
- [Qemu-block] [PATCH v2 05/12] vl: Improve legibility of BlockdevOptions queue, Markus Armbruster, 2019/03/07
- [Qemu-block] [PATCH v2 07/12] vl: Create block backends before setting machine properties, Markus Armbruster, 2019/03/07