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?
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:
