On Thu, Oct 23, 2025 at 8:21 PM Kevin Wolf <[email protected]> wrote:
>
> Am 03.09.2025 um 09:57 hat Clément Chigot geschrieben:
> > This option when set prevents a master boot record (MBR) to be
> > initialized. This is mandatory as some operating system don't recognized
> > mounted disks if a MBR is present.
> >
> > Signed-off-by: Clément Chigot <[email protected]>
>
> Can we actually give an example of such an OS in the commit message?
>
> > ---
> > block/vvfat.c | 16 +++++++++++++++-
> > 1 file changed, 15 insertions(+), 1 deletion(-)
> >
> > diff --git a/block/vvfat.c b/block/vvfat.c
> > index 814796d918..0220dd828b 100644
> > --- a/block/vvfat.c
> > +++ b/block/vvfat.c
> > @@ -1082,6 +1082,11 @@ static QemuOptsList runtime_opts = {
> > .type = QEMU_OPT_BOOL,
> > .help = "Make the image writable",
> > },
> > + {
> > + .name = "no-mbr",
> > + .type = QEMU_OPT_BOOL,
> > + .help = "Do not add a Master Boot Record on this disk",
> > + },
>
> Let's keep option names positive to avoid double negations like
> 'no-mbr=false'. We can have an 'mbr' option that defaults to true. Or in
> fact, maybe calling it 'partitioned' would be easier to understand.
>
> You need to update BlockdevOptionsVVFAT in qapi/block-core.json, too, to
> make the new option work with -blockdev. You should update the
> description for @floppy there, too, because it says that hard disks are
> always partitioned.
>
> It should also be added to vvfat_strong_runtime_opts because the value
> of this option changes the data that the guest sees.
Just to keep you updated, I've seen your comments. I'm just waiting to
see where the discussion of patch 5 leads before pushing v2.
> > { /* end of list */ }
> > },
> > };
> > @@ -1092,6 +1097,7 @@ static void vvfat_parse_filename(const char
> > *filename, QDict *options,
> > int fat_type = 0;
> > bool floppy = false;
> > bool rw = false;
> > + bool no_mbr = false;
> > int i;
> >
> > if (!strstart(filename, "fat:", NULL)) {
> > @@ -1116,6 +1122,10 @@ static void vvfat_parse_filename(const char
> > *filename, QDict *options,
> > rw = true;
> > }
> >
> > + if (strstr(filename, ":no-mbr:")) {
>
> In the string, the negative form can stay (because the positive one
> doesn't exist here).
>
> > + no_mbr = true;
> > + }
> > +
> > /* Get the directory name without options */
> > i = strrchr(filename, ':') - filename;
> > assert(i >= 3);
> > @@ -1131,6 +1141,7 @@ static void vvfat_parse_filename(const char
> > *filename, QDict *options,
> > qdict_put_int(options, "fat-type", fat_type);
> > qdict_put_bool(options, "floppy", floppy);
> > qdict_put_bool(options, "rw", rw);
> > + qdict_put_bool(options, "no-mbr", no_mbr);
> > }
> >
> > static int vvfat_open(BlockDriverState *bs, QDict *options, int flags,
> > @@ -1196,7 +1207,10 @@ static int vvfat_open(BlockDriverState *bs, QDict
> > *options, int flags,
> > if (!s->fat_type) {
> > s->fat_type = 16;
> > }
> > - s->offset_to_bootsector = 0x3f;
> > + /* Reserver space for MBR */
> > + if (!qemu_opt_get_bool(opts, "no-mbr", false)) {
> > + s->offset_to_bootsector = 0x3f;
> > + }
> > cyls = s->fat_type == 12 ? 64 : 1024;
> > heads = 16;
> > secs = 63;
>
> Kevin
>
