include/hw/arm/virt.h | 1 - include/hw/boards.h | 1 + include/hw/core/generic-loader.h | 4 + include/hw/riscv/virt.h | 1 - include/sysemu/device_tree.h | 17 ++ device_tree.c | 26 +++ hw/arm/virt.c | 322 ++++++++++++++++--------------- hw/core/generic-loader.c | 42 ++++ hw/riscv/virt.c | 18 +- 9 files changed, 268 insertions(+), 164 deletions(-)
Hi,
This series adds the ability to append FDT data for blobs loaded by
the generic loader. My principle use-case was to be able to directly
boot Xen with a kernel image which avoided having to:
- get the kernel image into my system image
- deal with bugs in FDT munging by -bios firmware and/or grub
as such this currently a developer hack that makes *my* life easy and
is thus presented as an RFC for discussion. While I've tested it with
Xen I'm sure the approach would be applicable to other hypervisors or
firmware which expect to consume FDT data pointing at various blobs.
An example command line that launches this is (magic from -kernel):
./aarch64-softmmu/qemu-system-aarch64 -cpu cortex-a57 \
-machine type=virt,virtualization=on -display none \
-serial mon:stdio \
-netdev user,id=unet,hostfwd=tcp::2222-:22 \
-device virtio-net-pci,netdev=unet,id=virt-net,disable-legacy=on \
-device virtio-scsi-pci,id=virt-scsi,disable-legacy=on \
-blockdev driver=raw,node-name=hd,discard=unmap,file.driver=host_device,file.filename=/dev/zen-disk/debian-buster-arm64 \
-device scsi-hd,drive=hd,id=virt-scsi-hd \
-smp 4 -m 4096 \
-kernel ~/lsrc/xen.git/xen/xen \
-append "dom0_mem=1G,max:1G loglvl=all guest_loglvl=all" \
-device loader,addr=0x47000000,file=$HOME/lsrc/linux.git/builds/arm64/arch/arm64/boot/Image,len-fdt-compat=2,fdt-compat[0]='multiboot,,module',fdt-compat[1]='multiboot,,kernel',fdt-bootargs="root=/dev/sda2 ro console=hvc0 earlyprintk=xen"
So a couple of choices I've made doing this:
Promoting *fdt to MachineState
This seemed the simplest approach to making the fdt available to the
global state, especially as MachineState already has a *dtb pointer.
I've converted the ARM virt machine and a RISCV machine but if this is
acceptable I can convert the others.
"Polluting" the generic loader arguments
This was mainly out of convenience as the loader already knows the
size of the blob being loaded. However you could certainly argue it
makes sense to have a more generic "FDT expander" virtual device that
could for example query the QOM model somehow to find the details it
needs.
FDT isn't the only way of passing system information up the boot
chain. We could reasonably want to do a similar thing with ACPI which
is what should be being used on SBSA like devices to communicate with
the hypervisor.
Also relying on ,, in the QemuOpt parser is ugly. It might be worth
having better quoting support if I press on with this.
So what do people think? Something worth developing?
Alex Bennée (4):
hw/board: promote fdt from ARM VirtMachineState to MachineState
hw/riscv: migrate fdt field to generic MachineState
device_tree: add qemu_fdt_setprop_string_array helper
generic_loader: allow the insertion of /chosen/module stanzas
include/hw/arm/virt.h | 1 -
include/hw/boards.h | 1 +
include/hw/core/generic-loader.h | 4 +
include/hw/riscv/virt.h | 1 -
include/sysemu/device_tree.h | 17 ++
device_tree.c | 26 +++
hw/arm/virt.c | 322 ++++++++++++++++---------------
hw/core/generic-loader.c | 42 ++++
hw/riscv/virt.c | 18 +-
9 files changed, 268 insertions(+), 164 deletions(-)
--
2.20.1
Patchew URL: https://patchew.org/QEMU/20201009170742.23695-1-alex.bennee@linaro.org/
Hi,
This series seems to have some coding style problems. See output below for
more information:
Type: series
Message-id: 20201009170742.23695-1-alex.bennee@linaro.org
Subject: [RFC PATCH 0/4] generic loader FDT support (for direct Xen boot)
=== TEST SCRIPT BEGIN ===
#!/bin/bash
git rev-parse base > /dev/null || exit 0
git config --local diff.renamelimit 0
git config --local diff.renames True
git config --local diff.algorithm histogram
./scripts/checkpatch.pl --mailback base..
=== TEST SCRIPT END ===
Updating 3c8cf5a9c21ff8782164d1def7f44bd888713384
From https://github.com/patchew-project/qemu
* [new tag] patchew/20201009170742.23695-1-alex.bennee@linaro.org -> patchew/20201009170742.23695-1-alex.bennee@linaro.org
Switched to a new branch 'test'
8fbccbe generic_loader: allow the insertion of /chosen/module stanzas
2baf07a device_tree: add qemu_fdt_setprop_string_array helper
dd6eea3 hw/riscv: migrate fdt field to generic MachineState
dd8ee86 hw/board: promote fdt from ARM VirtMachineState to MachineState
=== OUTPUT BEGIN ===
1/4 Checking commit dd8ee86f5cdf (hw/board: promote fdt from ARM VirtMachineState to MachineState)
2/4 Checking commit dd6eea3e6e34 (hw/riscv: migrate fdt field to generic MachineState)
3/4 Checking commit 2baf07a7abfc (device_tree: add qemu_fdt_setprop_string_array helper)
WARNING: line over 80 characters
#35: FILE: device_tree.c:406:
+int qemu_fdt_setprop_string_array(void *fdt, const char *node_path, const char *prop,
total: 0 errors, 1 warnings, 61 lines checked
Patch 3/4 has style problems, please review. If any of these errors
are false positives report them to the maintainer, see
CHECKPATCH in MAINTAINERS.
4/4 Checking commit 8fbccbec9628 (generic_loader: allow the insertion of /chosen/module stanzas)
ERROR: Don't use '#' flag of printf format ('%#') in format strings, use '0x' prefix instead
#51: FILE: hw/core/generic-loader.c:73:
+ g_autofree char *node = g_strdup_printf("/chosen/module@%#08lx", s->addr);
WARNING: line over 80 characters
#71: FILE: hw/core/generic-loader.c:93:
+ if (qemu_fdt_setprop_string(fdt, node, "bootargs", s->fdt_bootargs) < 0) {
total: 1 errors, 1 warnings, 76 lines checked
Patch 4/4 has style problems, please review. If any of these errors
are false positives report them to the maintainer, see
CHECKPATCH in MAINTAINERS.
=== OUTPUT END ===
Test command exited with code: 1
The full log is available at
http://patchew.org/logs/20201009170742.23695-1-alex.bennee@linaro.org/testing.checkpatch/?type=message.
---
Email generated automatically by Patchew [https://patchew.org/].
Please send your feedback to patchew-devel@redhat.com
On Fri, Oct 9, 2020 at 10:07 AM Alex Bennée <alex.bennee@linaro.org> wrote: > > Hi, > > This series adds the ability to append FDT data for blobs loaded by > the generic loader. My principle use-case was to be able to directly > boot Xen with a kernel image which avoided having to: > > - get the kernel image into my system image > - deal with bugs in FDT munging by -bios firmware and/or grub > > as such this currently a developer hack that makes *my* life easy and > is thus presented as an RFC for discussion. While I've tested it with > Xen I'm sure the approach would be applicable to other hypervisors or > firmware which expect to consume FDT data pointing at various blobs. An interesting idea. I think this comes up enough that it's worth thinking about. > > An example command line that launches this is (magic from -kernel): > > ./aarch64-softmmu/qemu-system-aarch64 -cpu cortex-a57 \ > -machine type=virt,virtualization=on -display none \ > -serial mon:stdio \ > -netdev user,id=unet,hostfwd=tcp::2222-:22 \ > -device virtio-net-pci,netdev=unet,id=virt-net,disable-legacy=on \ > -device virtio-scsi-pci,id=virt-scsi,disable-legacy=on \ > -blockdev driver=raw,node-name=hd,discard=unmap,file.driver=host_device,file.filename=/dev/zen-disk/debian-buster-arm64 \ > -device scsi-hd,drive=hd,id=virt-scsi-hd \ > -smp 4 -m 4096 \ > -kernel ~/lsrc/xen.git/xen/xen \ > -append "dom0_mem=1G,max:1G loglvl=all guest_loglvl=all" \ > -device loader,addr=0x47000000,file=$HOME/lsrc/linux.git/builds/arm64/arch/arm64/boot/Image,len-fdt-compat=2,fdt-compat[0]='multiboot,,module',fdt-compat[1]='multiboot,,kernel',fdt-bootargs="root=/dev/sda2 ro console=hvc0 earlyprintk=xen" You are loading the kernel `Image` file, but changing the device tree that was generated by QEMU and is being loaded in memory. As a user that is really confusing. > > So a couple of choices I've made doing this: > > Promoting *fdt to MachineState > > This seemed the simplest approach to making the fdt available to the > global state, especially as MachineState already has a *dtb pointer. > I've converted the ARM virt machine and a RISCV machine but if this is > acceptable I can convert the others. This seems fine to me. > > "Polluting" the generic loader arguments > > This was mainly out of convenience as the loader already knows the > size of the blob being loaded. However you could certainly argue it > makes sense to have a more generic "FDT expander" virtual device that > could for example query the QOM model somehow to find the details it > needs. That seems like a better option. Why not have a generic way to modify the device tree with a specific argument? It could either be -device loader,file=fdt,... or -fdt ... Alistair > > FDT isn't the only way of passing system information up the boot > chain. We could reasonably want to do a similar thing with ACPI which > is what should be being used on SBSA like devices to communicate with > the hypervisor. > > Also relying on ,, in the QemuOpt parser is ugly. It might be worth > having better quoting support if I press on with this. > > So what do people think? Something worth developing? > > > Alex Bennée (4): > hw/board: promote fdt from ARM VirtMachineState to MachineState > hw/riscv: migrate fdt field to generic MachineState > device_tree: add qemu_fdt_setprop_string_array helper > generic_loader: allow the insertion of /chosen/module stanzas > > include/hw/arm/virt.h | 1 - > include/hw/boards.h | 1 + > include/hw/core/generic-loader.h | 4 + > include/hw/riscv/virt.h | 1 - > include/sysemu/device_tree.h | 17 ++ > device_tree.c | 26 +++ > hw/arm/virt.c | 322 ++++++++++++++++--------------- > hw/core/generic-loader.c | 42 ++++ > hw/riscv/virt.c | 18 +- > 9 files changed, 268 insertions(+), 164 deletions(-) > > -- > 2.20.1 > >
Alistair Francis <alistair23@gmail.com> writes: > On Fri, Oct 9, 2020 at 10:07 AM Alex Bennée <alex.bennee@linaro.org> wrote: >> >> Hi, >> >> This series adds the ability to append FDT data for blobs loaded by >> the generic loader. My principle use-case was to be able to directly >> boot Xen with a kernel image which avoided having to: >> >> - get the kernel image into my system image >> - deal with bugs in FDT munging by -bios firmware and/or grub >> >> as such this currently a developer hack that makes *my* life easy and >> is thus presented as an RFC for discussion. While I've tested it with >> Xen I'm sure the approach would be applicable to other hypervisors or >> firmware which expect to consume FDT data pointing at various blobs. > > An interesting idea. I think this comes up enough that it's worth > thinking about. > >> >> An example command line that launches this is (magic from -kernel): >> >> ./aarch64-softmmu/qemu-system-aarch64 -cpu cortex-a57 \ >> -machine type=virt,virtualization=on -display none \ >> -serial mon:stdio \ >> -netdev user,id=unet,hostfwd=tcp::2222-:22 \ >> -device virtio-net-pci,netdev=unet,id=virt-net,disable-legacy=on \ >> -device virtio-scsi-pci,id=virt-scsi,disable-legacy=on \ >> -blockdev driver=raw,node-name=hd,discard=unmap,file.driver=host_device,file.filename=/dev/zen-disk/debian-buster-arm64 \ >> -device scsi-hd,drive=hd,id=virt-scsi-hd \ >> -smp 4 -m 4096 \ >> -kernel ~/lsrc/xen.git/xen/xen \ >> -append "dom0_mem=1G,max:1G loglvl=all guest_loglvl=all" \ >> -device loader,addr=0x47000000,file=$HOME/lsrc/linux.git/builds/arm64/arch/arm64/boot/Image,len-fdt-compat=2,fdt-compat[0]='multiboot,,module',fdt-compat[1]='multiboot,,kernel',fdt-bootargs="root=/dev/sda2 ro console=hvc0 earlyprintk=xen" > > You are loading the kernel `Image` file, but changing the device tree > that was generated by QEMU and is being loaded in memory. As a user > that is really confusing. Well in this case the "kernel" is Xen which helpfully comes with a kernel compatible header that the kernel loaded understand. The blob could be any Dom0 kernel - it just happens to be a Linux kernel in this case. > >> >> So a couple of choices I've made doing this: >> >> Promoting *fdt to MachineState >> >> This seemed the simplest approach to making the fdt available to the >> global state, especially as MachineState already has a *dtb pointer. >> I've converted the ARM virt machine and a RISCV machine but if this is >> acceptable I can convert the others. > > This seems fine to me. > >> >> "Polluting" the generic loader arguments >> >> This was mainly out of convenience as the loader already knows the >> size of the blob being loaded. However you could certainly argue it >> makes sense to have a more generic "FDT expander" virtual device that >> could for example query the QOM model somehow to find the details it >> needs. > > That seems like a better option. Why not have a generic way to modify > the device tree with a specific argument? It could either be -device > loader,file=fdt,... or -fdt ... Well it comes down to how much of a special case this is? Pretty much all FDT (and ACPI for the matter) is basically down to the board level models - and not all of them just the funky configurable ones. For other board models we just expect the user to pass the FDT they got with their kernel blob. For modern VirtIO systems the only thing you really need to expose is the root PCI bus because the rest of the devices are discover-able there. So the real question is are there any other -devices that we want to be able to graft FDT entries on or is the generic loader enough of a special case that we keep all the logic in there? > > Alistair > >> >> FDT isn't the only way of passing system information up the boot >> chain. We could reasonably want to do a similar thing with ACPI which >> is what should be being used on SBSA like devices to communicate with >> the hypervisor. >> >> Also relying on ,, in the QemuOpt parser is ugly. It might be worth >> having better quoting support if I press on with this. >> >> So what do people think? Something worth developing? >> >> >> Alex Bennée (4): >> hw/board: promote fdt from ARM VirtMachineState to MachineState >> hw/riscv: migrate fdt field to generic MachineState >> device_tree: add qemu_fdt_setprop_string_array helper >> generic_loader: allow the insertion of /chosen/module stanzas >> >> include/hw/arm/virt.h | 1 - >> include/hw/boards.h | 1 + >> include/hw/core/generic-loader.h | 4 + >> include/hw/riscv/virt.h | 1 - >> include/sysemu/device_tree.h | 17 ++ >> device_tree.c | 26 +++ >> hw/arm/virt.c | 322 ++++++++++++++++--------------- >> hw/core/generic-loader.c | 42 ++++ >> hw/riscv/virt.c | 18 +- >> 9 files changed, 268 insertions(+), 164 deletions(-) >> >> -- >> 2.20.1 >> >> -- Alex Bennée
On Mon, 12 Oct 2020 at 17:19, Alex Bennée <alex.bennee@linaro.org> wrote: > So the real question is are there any other -devices that we want to be > able to graft FDT entries on or is the generic loader enough of a > special case that we keep all the logic in there? To my mind the point of the generic loader is exactly that it is not a special case. It works exactly the same way for every board, for every architecture. It shouldn't have special case "this makes things work for the thing I want to load on these boards that all have FDT and want a particular change to it". We already have a loader that has that kind of "do what I mean" behaviour (--kernel), and I very much do not want the generic loader device to go in that direction. Its whole advantage is that it is not that, but is just a "load the file, nothing else, no magic" operation. thanks -- PMM
Peter Maydell <peter.maydell@linaro.org> writes: > On Mon, 12 Oct 2020 at 17:19, Alex Bennée <alex.bennee@linaro.org> wrote: >> So the real question is are there any other -devices that we want to be >> able to graft FDT entries on or is the generic loader enough of a >> special case that we keep all the logic in there? > > To my mind the point of the generic loader is exactly that > it is not a special case. It works exactly the same way > for every board, for every architecture. It shouldn't have > special case "this makes things work for the thing I want > to load on these boards that all have FDT and want a > particular change to it". We already have a loader that > has that kind of "do what I mean" behaviour (--kernel), > and I very much do not want the generic loader device to > go in that direction. Its whole advantage is that it is > not that, but is just a "load the file, nothing else, > no magic" operation. So should we introduce a sub-classed -device guest-loader which behaves like generic loader except that it is also aware of platform data issues? The other option would be to add the logic to each board that supports dynamic platform data. It would keep the problem bounded but also lead to a fair amount of duplicated boiler-plate. > > thanks > -- PMM -- Alex Bennée
On Mon, Oct 12, 2020 at 05:02:57PM +0100, Alex Bennée wrote: > > Alistair Francis <alistair23@gmail.com> writes: > > > On Fri, Oct 9, 2020 at 10:07 AM Alex Bennée <alex.bennee@linaro.org> wrote: > >> > >> Hi, > >> > >> This series adds the ability to append FDT data for blobs loaded by > >> the generic loader. My principle use-case was to be able to directly > >> boot Xen with a kernel image which avoided having to: > >> > >> - get the kernel image into my system image > >> - deal with bugs in FDT munging by -bios firmware and/or grub > >> > >> as such this currently a developer hack that makes *my* life easy and > >> is thus presented as an RFC for discussion. While I've tested it with > >> Xen I'm sure the approach would be applicable to other hypervisors or > >> firmware which expect to consume FDT data pointing at various blobs. > > > > An interesting idea. I think this comes up enough that it's worth > > thinking about. > > > >> > >> An example command line that launches this is (magic from -kernel): > >> > >> ./aarch64-softmmu/qemu-system-aarch64 -cpu cortex-a57 \ > >> -machine type=virt,virtualization=on -display none \ > >> -serial mon:stdio \ > >> -netdev user,id=unet,hostfwd=tcp::2222-:22 \ > >> -device virtio-net-pci,netdev=unet,id=virt-net,disable-legacy=on \ > >> -device virtio-scsi-pci,id=virt-scsi,disable-legacy=on \ > >> -blockdev driver=raw,node-name=hd,discard=unmap,file.driver=host_device,file.filename=/dev/zen-disk/debian-buster-arm64 \ > >> -device scsi-hd,drive=hd,id=virt-scsi-hd \ > >> -smp 4 -m 4096 \ > >> -kernel ~/lsrc/xen.git/xen/xen \ > >> -append "dom0_mem=1G,max:1G loglvl=all guest_loglvl=all" \ > >> -device loader,addr=0x47000000,file=$HOME/lsrc/linux.git/builds/arm64/arch/arm64/boot/Image,len-fdt-compat=2,fdt-compat[0]='multiboot,,module',fdt-compat[1]='multiboot,,kernel',fdt-bootargs="root=/dev/sda2 ro console=hvc0 earlyprintk=xen" > > > > You are loading the kernel `Image` file, but changing the device tree > > that was generated by QEMU and is being loaded in memory. As a user > > that is really confusing. > > Well in this case the "kernel" is Xen which helpfully comes with a > kernel compatible header that the kernel loaded understand. The blob > could be any Dom0 kernel - it just happens to be a Linux kernel in this > case. > > > > >> > >> So a couple of choices I've made doing this: > >> > >> Promoting *fdt to MachineState > >> > >> This seemed the simplest approach to making the fdt available to the > >> global state, especially as MachineState already has a *dtb pointer. > >> I've converted the ARM virt machine and a RISCV machine but if this is > >> acceptable I can convert the others. > > > > This seems fine to me. > > > >> > >> "Polluting" the generic loader arguments > >> > >> This was mainly out of convenience as the loader already knows the > >> size of the blob being loaded. However you could certainly argue it > >> makes sense to have a more generic "FDT expander" virtual device that > >> could for example query the QOM model somehow to find the details it > >> needs. > > > > That seems like a better option. Why not have a generic way to modify > > the device tree with a specific argument? It could either be -device > > loader,file=fdt,... or -fdt ... > > Well it comes down to how much of a special case this is? Pretty much > all FDT (and ACPI for the matter) is basically down to the board level > models - and not all of them just the funky configurable ones. For other > board models we just expect the user to pass the FDT they got with their > kernel blob. > > For modern VirtIO systems the only thing you really need to expose is > the root PCI bus because the rest of the devices are discover-able > there. > > So the real question is are there any other -devices that we want to be > able to graft FDT entries on or is the generic loader enough of a > special case that we keep all the logic in there? > Hi, Another option is to allow the user to pass along a DTB overlay with the generic loader option (or with a separate option as Alistair suggested). With overlways we wouldn't need all the command-line options to enable construction of dtb fragments, it would be more or less transparent to QEMU. There may be limitations with the overlay flows that I'm not aware of though... Cheers, Edgar
Edgar E. Iglesias <edgar.iglesias@gmail.com> writes: > On Mon, Oct 12, 2020 at 05:02:57PM +0100, Alex Bennée wrote: >> >> Alistair Francis <alistair23@gmail.com> writes: >> >> > On Fri, Oct 9, 2020 at 10:07 AM Alex Bennée <alex.bennee@linaro.org> wrote: >> >> >> >> Hi, >> >> >> >> This series adds the ability to append FDT data for blobs loaded by >> >> the generic loader. My principle use-case was to be able to directly >> >> boot Xen with a kernel image which avoided having to: >> >> >> >> - get the kernel image into my system image >> >> - deal with bugs in FDT munging by -bios firmware and/or grub <snip> >> >> "Polluting" the generic loader arguments >> >> >> >> This was mainly out of convenience as the loader already knows the >> >> size of the blob being loaded. However you could certainly argue it >> >> makes sense to have a more generic "FDT expander" virtual device that >> >> could for example query the QOM model somehow to find the details it >> >> needs. >> > >> > That seems like a better option. Why not have a generic way to modify >> > the device tree with a specific argument? It could either be -device >> > loader,file=fdt,... or -fdt ... >> >> Well it comes down to how much of a special case this is? Pretty much >> all FDT (and ACPI for the matter) is basically down to the board level >> models - and not all of them just the funky configurable ones. For other >> board models we just expect the user to pass the FDT they got with their >> kernel blob. >> >> For modern VirtIO systems the only thing you really need to expose is >> the root PCI bus because the rest of the devices are discover-able >> there. >> >> So the real question is are there any other -devices that we want to be >> able to graft FDT entries on or is the generic loader enough of a >> special case that we keep all the logic in there? >> > > Hi, > > Another option is to allow the user to pass along a DTB overlay with the > generic loader option (or with a separate option as Alistair suggested). > With overlways we wouldn't need all the command-line options to enable > construction of dtb fragments, it would be more or less transparent to > QEMU. There may be limitations with the overlay flows that I'm not aware > of though... So the problem of adding DTB overlays is it's not that much easier than the current options of using -machine dumpdtb and then hand hacking the magic values and rebuilding, for example: https://medium.com/@denisobrezkov/xen-on-arm-and-qemu-1654f24dea75 Unless we come up with some sort of template support that allows QEMU to insert numbers like address and size while processing the template. But that seems a little too over engineered and likely introduces complexity into the system. Given the generic-loader is so simple I'm leaning towards another approach of just c&p'ing generic-loader into a new "magic" device (maybe guest-loader) and stripping out the bits we don't need (data, data-len, be etc) and making the options more tuned what we are trying to achieve. For example: -device guest-loader,kernel=path/to/Image,args="command line",addr=0x47000000,hyp=xen -device guest-loader,initrd=path/to/initrd,addr=0x42000000,hyp=xen And then we can embed the smarts in the loader to set either DTB or ACPI entries as required and if we need additional magic to support different hypervisors (which hopefully you don't but...) you can modulate the hyp=FOO variable. There may be an argument for having a -hypervisor as a sugar alias for -kernel (which maps to machine.kernel) but currently I see no practical differences you need to launch it except maybe forcing the virtualisation property to true if it exists - but that seems a little ARM focused. -- Alex Bennée
On Tue, Oct 13, 2020 at 3:11 AM Alex Bennée <alex.bennee@linaro.org> wrote: > > > Edgar E. Iglesias <edgar.iglesias@gmail.com> writes: > > > On Mon, Oct 12, 2020 at 05:02:57PM +0100, Alex Bennée wrote: > >> > >> Alistair Francis <alistair23@gmail.com> writes: > >> > >> > On Fri, Oct 9, 2020 at 10:07 AM Alex Bennée <alex.bennee@linaro.org> wrote: > >> >> > >> >> Hi, > >> >> > >> >> This series adds the ability to append FDT data for blobs loaded by > >> >> the generic loader. My principle use-case was to be able to directly > >> >> boot Xen with a kernel image which avoided having to: > >> >> > >> >> - get the kernel image into my system image > >> >> - deal with bugs in FDT munging by -bios firmware and/or grub > <snip> > >> >> "Polluting" the generic loader arguments > >> >> > >> >> This was mainly out of convenience as the loader already knows the > >> >> size of the blob being loaded. However you could certainly argue it > >> >> makes sense to have a more generic "FDT expander" virtual device that > >> >> could for example query the QOM model somehow to find the details it > >> >> needs. > >> > > >> > That seems like a better option. Why not have a generic way to modify > >> > the device tree with a specific argument? It could either be -device > >> > loader,file=fdt,... or -fdt ... > >> > >> Well it comes down to how much of a special case this is? Pretty much > >> all FDT (and ACPI for the matter) is basically down to the board level > >> models - and not all of them just the funky configurable ones. For other > >> board models we just expect the user to pass the FDT they got with their > >> kernel blob. > >> > >> For modern VirtIO systems the only thing you really need to expose is > >> the root PCI bus because the rest of the devices are discover-able > >> there. > >> > >> So the real question is are there any other -devices that we want to be > >> able to graft FDT entries on or is the generic loader enough of a > >> special case that we keep all the logic in there? > >> > > > > Hi, > > > > Another option is to allow the user to pass along a DTB overlay with the > > generic loader option (or with a separate option as Alistair suggested). > > With overlways we wouldn't need all the command-line options to enable > > construction of dtb fragments, it would be more or less transparent to > > QEMU. There may be limitations with the overlay flows that I'm not aware > > of though... > > So the problem of adding DTB overlays is it's not that much easier than > the current options of using -machine dumpdtb and then hand hacking the > magic values and rebuilding, for example: I agree with this. If a user is changing a DTB from a command line they probably only want small changes and are unlikely to need the full power of an overlay. > > https://medium.com/@denisobrezkov/xen-on-arm-and-qemu-1654f24dea75 > > Unless we come up with some sort of template support that allows QEMU to > insert numbers like address and size while processing the template. But > that seems a little too over engineered and likely introduces complexity > into the system. This though sounds interesting :) > > Given the generic-loader is so simple I'm leaning towards another > approach of just c&p'ing generic-loader into a new "magic" device (maybe > guest-loader) and stripping out the bits we don't need (data, data-len, > be etc) and making the options more tuned what we are trying to achieve. > For example: > > -device guest-loader,kernel=path/to/Image,args="command line",addr=0x47000000,hyp=xen > -device guest-loader,initrd=path/to/initrd,addr=0x42000000,hyp=xen At first I'm not thrilled of adding a new loader. In saying that, there are lots of times where -kernel and friends doesn't do what I want it to do and I have to fall back to the generic loader and code changes to QEMU so maybe this is a good idea for image loading. I'm guessing this would be the same for every platform which would be a nice change from -kernel. Alistair > > And then we can embed the smarts in the loader to set either DTB or ACPI > entries as required and if we need additional magic to support different > hypervisors (which hopefully you don't but...) you can modulate the > hyp=FOO variable. > > There may be an argument for having a -hypervisor as a sugar alias for > -kernel (which maps to machine.kernel) but currently I see no practical > differences you need to launch it except maybe forcing the > virtualisation property to true if it exists - but that seems a little > ARM focused. > > -- > Alex Bennée
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