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

[Alex Bennée]

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 correct
plumbing has been done for the machine? Anything I can look for to audit
other machine types?

>
>
> 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 |


-- 
Alex Bennée