Re: [PATCH v2 1/5] vvfat: introduce partitioned option

[Kevin Wolf <kwolf@redhat.com>]

Am 10.11.2025 um 14:20 hat Markus Armbruster geschrieben:
> BALATON Zoltan <balaton@eik.bme.hu> writes:
> 
> > On Mon, 10 Nov 2025, Clément Chigot wrote:
> >> On Mon, Nov 10, 2025 at 11:07 AM Markus Armbruster <armbru@redhat.com> wrote:
> >>>
> >>> Clément Chigot <chigot@adacore.com> writes:
> >>>
> >>>> This option tells whether a hard disk should be partitioned or not. It
> >>>> defaults to true and have the prime effect of preventing a master boot
> >>>> record (MBR) to be initialized.
> >>>>
> >>>> This is useful as some operating system (QNX, Rtems) don't
> >>>> recognized FAT mounted disks (especially SD cards) if a MBR is present.
> >>>>
> >>>> Signed-off-by: Clément Chigot <chigot@adacore.com>
> >>>
> >>> [...]
> >>>
> >>>> diff --git a/qapi/block-core.json b/qapi/block-core.json
> >>>> index b82af74256..8a479ba090 100644
> >>>> --- a/qapi/block-core.json
> >>>> +++ b/qapi/block-core.json
> >>>> @@ -3464,8 +3464,8 @@
> >>>>  #
> >>>>  # @fat-type: FAT type: 12, 16 or 32
> >>>>  #
> >>>> -# @floppy: whether to export a floppy image (true) or partitioned hard
> >>>> -#     disk (false; default)
> >>>> +# @floppy: whether to export a floppy image (true) or hard disk
> >>>> +#     (false; default)
> >>>>  #
> >>>>  # @label: set the volume label, limited to 11 bytes.  FAT16 and FAT32
> >>>>  #     traditionally have some restrictions on labels, which are
> >>>> @@ -3474,11 +3474,15 @@
> >>>>  #
> >>>>  # @rw: whether to allow write operations (default: false)
> >>>>  #
> >>>> +# @partitioned: whether a hard disk will be partitioned
> >>>
> >>> How does "partitioned" combine with "floppy": true?
> >>>
> >>> Is it silently ignored?
> >>>
> >>> Is it an error if present?
> >>>
> >>> Is it an error if true?
> >>>
> >>> Does it add a partition table if true?
> >>>
> >>>> +#     (default: true)
> >>>
> >>> Hmm, this suggests it's silently ignored.
> >>>
> >>> Silently ignoring nonsensical configuration is usually a bad idea.
> >>
> >> True, but that would mean "unpartitioned" must always be passed when
> >> "floppy" is requested. That would make such command lines a bit more
> >> verbose, but otherwise I don't think there is any issue to that.
> >>
> >> Note that I didn't add "partition" as a keyword in the command line.
> >> Currently, it's either the default (thus partitioned) or
> >> "unpartitioned" being requested. Do you think it makes sense to add it
> >> as well, even if it's redundant ?
> >>
> >>>> +#     (since 10.2)
> >>>> +#
> >>>
> >>> Not sure I like "partitioned".  Is a disk with an MBR and a partition
> >>> table contraining a single partition partitioned?  Call it "mbr"?
> >>
> >> It used to be called "mbr/no-mbr" but Kevin suggested renaming it in
> >> V1. Honestly I'm fine with both options:
> >> - Technically, the option prevents MBR which has a side effect for
> >> preventing partition tables
> 
> Yes, because the partition table is part of the MBR.  I'd rather name
> the option after the entire thing it controls, not one of its parts.
> 
> >> - Even it has a single partition, I think it makes sense to call a
> >> disk "partitioned" as long as it has a partition table
> >>
> >> But I'm not that familiar with disk formats, etc. I'll let you decide
> >> with Kevin, which one you prefer.
> 
> Kevin is the maintainer, I just serve as advisor here.

I figured that the meaning of "partitioned" is easier to understand for
a casual user than having or not having an MBR ("I don't want to boot
from this disk, why would I care about a boot record?").

But if people think that "mbr" is better, that's fine with me.

The only thing I really didn't want is the negative "no-mbr" and the
double negation in "no-mbr=off" that comes with it.

> > I'd also vote for mbr or similar shorter name; unpartitioned is
> > awkward to type out in a command line. Maybe it can default to false
> > for floppy and true for disk to preserve current behaviour but allow
> > controlling it.
> 
> I'm not a fan of conditional defaults, but I think it's better than a
> nonsensical default that gets ignored.

I think in this case a conditional default makes sense, not only for
compatibility reasons. Hard disks almost always have a partition, floppy
disks with partitions are basically unheard of.

Kevin