"
On Thu, Nov 27, 2025 at 3:40 PM BALATON Zoltan <[email protected]> wrote:
>
> On Thu, 27 Nov 2025, Clément Chigot wrote:
> > This option tells whether the volume should be partitioned or not. Its
> > default varies: true for hard disks and false for floppy. Its prime
> > effect is to prevent 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 <[email protected]>
> > ---
> > block/vvfat.c | 19 ++++++++++++++++---
> > qapi/block-core.json | 10 +++++++---
> > 2 files changed, 23 insertions(+), 6 deletions(-)
> >
> > diff --git a/block/vvfat.c b/block/vvfat.c
> > index 814796d918..dd0b3689c1 100644
> > --- a/block/vvfat.c
> > +++ b/block/vvfat.c
> > @@ -306,7 +306,8 @@ typedef struct BDRVVVFATState {
> > array_t fat,directory,mapping;
> > char volume_label[11];
> >
> > - uint32_t offset_to_bootsector; /* 0 for floppy, 0x3f for disk */
> > + /* 0x3f for partitioned disk, 0x0 otherwise */
> > + uint32_t offset_to_bootsector;
> >
> > unsigned int cluster_size;
> > unsigned int sectors_per_cluster;
> > @@ -1082,6 +1083,11 @@ static QemuOptsList runtime_opts = {
> > .type = QEMU_OPT_BOOL,
> > .help = "Make the image writable",
> > },
> > + {
> > + .name = "partitioned",
> > + .type = QEMU_OPT_BOOL,
> > + .help = "Do not add a Master Boot Record on this disk",
>
> Maybe should say "Add MBR to disk" and not "Do not add" as that's what
> true means now.
>
> > + },
> > { /* end of list */ }
> > },
> > };
> > @@ -1138,7 +1144,7 @@ static int vvfat_open(BlockDriverState *bs, QDict
> > *options, int flags,
> > {
> > BDRVVVFATState *s = bs->opaque;
> > int cyls, heads, secs;
> > - bool floppy;
> > + bool floppy, partitioned;
> > const char *dirname, *label;
> > QemuOpts *opts;
> > int ret;
> > @@ -1165,6 +1171,9 @@ static int vvfat_open(BlockDriverState *bs, QDict
> > *options, int flags,
> > s->fat_type = qemu_opt_get_number(opts, "fat-type", 0);
> > floppy = qemu_opt_get_bool(opts, "floppy", false);
> >
> > + /* Hard disk are partitioned by default; floppy aren't. */
>
> Singular plural mismatch. Either disks/floppies are/aren't or is/isn't
> when singular.
>
> > + partitioned = qemu_opt_get_bool(opts, "partitioned", floppy ? false :
> > true);
> > +
> > memset(s->volume_label, ' ', sizeof(s->volume_label));
> > label = qemu_opt_get(opts, "label");
> > if (label) {
> > @@ -1196,7 +1205,6 @@ static int vvfat_open(BlockDriverState *bs, QDict
> > *options, int flags,
> > if (!s->fat_type) {
> > s->fat_type = 16;
> > }
> > - s->offset_to_bootsector = 0x3f;
> > cyls = s->fat_type == 12 ? 64 : 1024;
> > heads = 16;
> > secs = 63;
> > @@ -1215,6 +1223,10 @@ static int vvfat_open(BlockDriverState *bs, QDict
> > *options, int flags,
> > goto fail;
> > }
> >
> > + /* Reserver space for MBR */
> > + if (partitioned) {
> > + s->offset_to_bootsector = 0x3f;
> > + }
> >
> > s->bs = bs;
> >
> > @@ -3246,6 +3258,7 @@ static const char *const vvfat_strong_runtime_opts[]
> > = {
> > "floppy",
> > "label",
> > "rw",
> > + "partitioned",
>
> Does this also needs to be parsed in vvfat_parse_filename like other
> options seem to be?
It used to be the case, but I've removed that possibility in v3. This
"vvfat_parse_filename" looks like a "hack" to ease setting vvfat
options when instantiating such blocks through the format=raw.
However, options can still be passed using "file." prefix. For
example, "format=raw,file.partitioned=false" will create an
unpartitioned vvfat block.
Overall, I think avoiding new options in the filename is a better
cleaner approach.
> >
> > NULL
> > };
> > diff --git a/qapi/block-core.json b/qapi/block-core.json
> > index b82af74256..ca438fba51 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)
>
> I was wondering what does this option do now. It seems to restrict size to
> different values, maybe that could be explained here.
>
> Regards,
> BALATON Zoltan
>
> > #
> > # @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 the volume will be partitioned;
> > +# (default: true for hard disk, false for floppy)
> > +# (since 10.2)
> > +#
> > # Since: 2.9
> > ##
> > { 'struct': 'BlockdevOptionsVVFAT',
> > 'data': { 'dir': 'str', '*fat-type': 'int', '*floppy': 'bool',
> > - '*label': 'str', '*rw': 'bool' } }
> > + '*label': 'str', '*rw': 'bool', '*partitioned': 'bool' } }
> >
> > ##
> > # @BlockdevOptionsGenericFormat:
> >
