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From: | Cédric Le Goater |
Subject: | Re: [RFC PATCH] qemu-options: bring the kernel and image options together |
Date: | Tue, 28 Jun 2022 08:11:38 +0200 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.0 |
On 6/23/22 12:21, Alex Bennée wrote:
Cédric Le Goater <clg@kaod.org> writes:On 6/22/22 16:50, Alex Bennée wrote:How to control the booting of QEMU is often a source of confusion for users. Bring the options that control this together in the manual pages and add some verbiage to describe when each option is appropriate. Signed-off-by: Alex Bennée <alex.bennee@linaro.org> Cc: Cédric Le Goater <clg@kaod.org> --- qemu-options.hx | 80 ++++++++++++++++++++++++++++++++++++++----------- 1 file changed, 62 insertions(+), 18 deletions(-) diff --git a/qemu-options.hx b/qemu-options.hx index 377d22fbd8..9b0242f0ef 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -1585,13 +1585,6 @@ SRST Use file as SecureDigital card image. ERST -DEF("pflash", HAS_ARG, QEMU_OPTION_pflash, - "-pflash file use 'file' as a parallel flash image\n", QEMU_ARCH_ALL) -SRST -``-pflash file`` - Use file as a parallel flash image. -ERST -> DEF("snapshot", 0, QEMU_OPTION_snapshot, "-snapshot write to temporary files instead of disk image files\n", QEMU_ARCH_ALL) @@ -3680,12 +3673,51 @@ DEFHEADING() #endif -DEFHEADING(Linux/Multiboot boot specific:) +DEFHEADING(Boot Image or Kernel specific:) +SRST +There are broadly 4 ways you can boot a system with QEMU. + + - specify a firmware and let it control finding a kernel + - specify a firmware and pass a hint to the kernel to boot + - direct kernel image boot + - manually load files into the guests address space + +The last method is useful for quickly testing kernels but as there is +no firmware to pass configuration information to the kernel it must +either be built for the exact configuration or be handed a DTB blob +which tells the kernel what drivers it needs.The last method can also load any FW blob with the correct executable layout (reset vector).Heh - actually I wrote that paragraph for the direct kernel image boot and then added the manual option after the fact. I'll try and clean that up to make it clearer.+ +ERST + +SRST + +For x86 machines ``-bios`` will generally do the right thing with +whatever it is given. For non-x86 machines the more strict ``-pflash`` +option needs an image that is sized for the flash device for the given +machine type.Some ppc machine use -bios also, mac, pseries, PowerNV (let's not restrict to x86).Ahh the magic some ;-) Does it essentially rely on if the correctplumbing has been done for the machine?
They rely on finding a reset vector. So yes, the FW should be mapped where it is expected and have vectors. The machines also know how to expose kernel/initrd to the FW and the FWs have runtime services. It's more than a kernel loader.
Anything I can look for to audit other machine types?
Good question. There are some many ways to start a machine. The avocado tests should be a good reference and here is a little tool I use to verify that the PPC machines supported in QEMU boot correctly : https://github.com/legoater/qemu-ppc-boot/blob/main/ppc-boot.sh Sometime ago, I did a model for a MicroWatt SoC, a POWER9 FPGA implementation, and I found quite a few ways to boot from some blob. See : https://github.com/qemu/qemu/commit/2f43989f87332c226358c1f3ef7b96d94ba342ca I guess when FW runtime services are required so is -bios. Else all these options : -kernel -bios -device loader -drive <flash> can be used more or less in the same way. Thanks, C.
LGTM. Thanks, C.+ +ERST + +DEF("bios", HAS_ARG, QEMU_OPTION_bios, \ + "-bios file set the filename for the BIOS\n", QEMU_ARCH_ALL) +SRST +``-bios file`` + Set the filename for the BIOS. +ERST + +DEF("pflash", HAS_ARG, QEMU_OPTION_pflash, + "-pflash file use 'file' as a parallel flash image\n", QEMU_ARCH_ALL) +SRST +``-pflash file`` + Use file as a parallel flash image. +ERST + SRST -When using these options, you can use a given Linux or Multiboot kernel -without installing it in the disk image. It can be useful for easier -testing of various kernels. +The kernel options were designed to work with Linux kernels although +other things (like hypervisors) can be packaged up as a kernel +executable image. The exact format of a executable image is usually +architecture specific. ERST @@ -3725,6 +3757,25 @@ SRST kernel on boot. ERST +SRST + +Finally you can also manually load images directly into the address +space of the guest. This is most useful for developers who already +know the layout of their guest and take care to ensure something sane +will happen when the reset vector executes. + +The generic loader can be invoked by using the loader device: + +``-device loader,addr=<addr>,data=<data>,data-len=<data-len>[,data-be=<data-be>][,cpu-num=<cpu-num>]`` + +there is also the guest loader which operates in a similar way but +tweaks the DTB so a hypervisor loaded via ``-kernel`` can find where +the guest image is: + +``-device guest-loader,addr=<addr>[,kernel=<path>,[bootargs=<arguments>]][,initrd=<path>]`` +ERST + DEFHEADING() DEFHEADING(Debug/Expert options:) @@ -4175,13 +4226,6 @@ SRST To list all the data directories, use ``-L help``. ERST -DEF("bios", HAS_ARG, QEMU_OPTION_bios, \ - "-bios file set the filename for the BIOS\n", QEMU_ARCH_ALL) -SRST -``-bios file`` - Set the filename for the BIOS. -ERST - DEF("enable-kvm", 0, QEMU_OPTION_enable_kvm, \ "-enable-kvm enable KVM full virtualization support\n", QEMU_ARCH_ARM | QEMU_ARCH_I386 | QEMU_ARCH_MIPS | QEMU_ARCH_PPC |
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