Re: [RFC PATCH] qemu-options: bring the kernel and image options together

[Cédric Le Goater]

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).


> +
> +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).


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 |