Re: [Qemu-devel] [PATCH v3 05/16] pc: Make -no-fd-bootchk stick across boot order changes

[Markus Armbruster]

Anthony Liguori <address@hidden> writes:

> Markus Armbruster <address@hidden> writes:
>
>> Option -no-fd-bootchk asks the BIOS to attempt booting from a floppy
>> even when the boot sector signature isn't there, by setting a bit in
>> RTC CMOS.  It was added back in 2006 (commit 52ca8d6a).
>>
>> Two years later, commit 0ecdffbb added monitor command boot_set.
>> Implemented by new function pc_boot_set().  It unconditionally clears
>> the floppy signature bit in CMOS.
>>
>> Commit e0f084bf added -boot option once to automatically change the
>> boot order on first reset.  Reuses pc_boot_set(), thus also clears the
>> floppy signature bit.  Commit d9346e81 took care to preserve this
>> behavior.
>
> Quite a history there :-)
>
> Does anyone still use no-fd-bootchk?

No idea.

>                                       Do you know what the original
> use-case was?

Its commit message is of no help.  Best we got is the option
documentation:

    Disable boot signature checking for floppy disks in Bochs BIOS.  It
    may be needed to boot from old floppy disks.

As far as I can tell, SeaBIOS implements this, too.

>> Thus, -no-fd-bootchk applies to any number of boots.  Except it
>> applies just to the first boot with -boot once, and never after
>> boot_set.  Weird.  Make it stick instead: set the bit according to
>> -no-fd-bootchk in pc_boot_set().
>>
>> Signed-off-by: Markus Armbruster <address@hidden>
>
> Reviewed-by: Anthony Liguori <address@hidden>

Thanks!