The main goal of this series is to introduce a new option "size" within
the vvfat backend (patch 5). It allows more control over SD cards' size.
The value for "Number of Heads" and "Sectors per track" are based on SD
specifications Part 2.

This series also includes minor patches:
 - patch 1 introduces another option to remove the Master Boot Record
   (this is mandatory for QNX)
 - patch 2-4 are minor improvements easing the introducing of "size"
   option

This was tested on with a aarch64-linux kernel taken from
functional/aarch64/test-virt and on aarch64-qnx over raspi4b with a
workaround, not included here (the SD bus must be associated to the EMMC2
port instead of through GPIOs).

Clément Chigot (5):
  vvfat: introduce no-mbr option
  vvfat: move fat_type check prior to size setup
  vvfat: add a define for SECTOR_SIZE
  vvfat: move size parameters within driver structure
  vvfat: add support for "size" options

 block/vvfat.c | 279 ++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 213 insertions(+), 66 deletions(-)

-- 
2.34.1

On Wed, Sep 03, 2025 at 09:57:16AM +0200, Clément Chigot wrote:
> The main goal of this series is to introduce a new option "size" within
> the vvfat backend (patch 5). It allows more control over SD cards' size.
> The value for "Number of Heads" and "Sectors per track" are based on SD
> specifications Part 2.
> 
> This series also includes minor patches:
>  - patch 1 introduces another option to remove the Master Boot Record
>    (this is mandatory for QNX)
>  - patch 2-4 are minor improvements easing the introducing of "size"
>    option
> 
> This was tested on with a aarch64-linux kernel taken from
> functional/aarch64/test-virt and on aarch64-qnx over raspi4b with a
> workaround, not included here (the SD bus must be associated to the EMMC2
> port instead of through GPIOs).
> 
> Clément Chigot (5):
>   vvfat: introduce no-mbr option
>   vvfat: move fat_type check prior to size setup
>   vvfat: add a define for SECTOR_SIZE
>   vvfat: move size parameters within driver structure
>   vvfat: add support for "size" options
> 
>  block/vvfat.c | 279 ++++++++++++++++++++++++++++++++++++++------------
>  1 file changed, 213 insertions(+), 66 deletions(-)

(Thanks Markus for bringing this thread up)

I just wanted to say that a long time ago I wrote an nbdkit plugin
that was intended as a more sane replacement for vfat.  Since then
several more nbdkit plugins have been added.  They support arbitrary
sizes already.  The first one is the most direct replacement for vvfat
(although it doesn't support writes to the backing directory, because
that feature is insane).

https://libguestfs.org/nbdkit-floppy-plugin.1.html
https://libguestfs.org/nbdkit-iso-plugin.1.html
https://libguestfs.org/nbdkit-linuxdisk-plugin.1.html
https://libguestfs.org/nbdkit-tmpdisk-plugin.1.html

Very easy to use from qemu as documented here:

https://libguestfs.org/nbdkit-client.1.html#ATTACHING-NBD-DEVICES-TO-A-VIRTUAL-MACHINE

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
libguestfs lets you edit virtual machines.  Supports shell scripting,
bindings from many languages.  http://libguestfs.org

On Wed, Nov 12, 2025 at 1:38 PM Richard W.M. Jones <rjones@redhat.com> wrote:
>
> On Wed, Sep 03, 2025 at 09:57:16AM +0200, Clément Chigot wrote:
> > The main goal of this series is to introduce a new option "size" within
> > the vvfat backend (patch 5). It allows more control over SD cards' size.
> > The value for "Number of Heads" and "Sectors per track" are based on SD
> > specifications Part 2.
> >
> > This series also includes minor patches:
> >  - patch 1 introduces another option to remove the Master Boot Record
> >    (this is mandatory for QNX)
> >  - patch 2-4 are minor improvements easing the introducing of "size"
> >    option
> >
> > This was tested on with a aarch64-linux kernel taken from
> > functional/aarch64/test-virt and on aarch64-qnx over raspi4b with a
> > workaround, not included here (the SD bus must be associated to the EMMC2
> > port instead of through GPIOs).
> >
> > Clément Chigot (5):
> >   vvfat: introduce no-mbr option
> >   vvfat: move fat_type check prior to size setup
> >   vvfat: add a define for SECTOR_SIZE
> >   vvfat: move size parameters within driver structure
> >   vvfat: add support for "size" options
> >
> >  block/vvfat.c | 279 ++++++++++++++++++++++++++++++++++++++------------
> >  1 file changed, 213 insertions(+), 66 deletions(-)
>
> (Thanks Markus for bringing this thread up)
>
> I just wanted to say that a long time ago I wrote an nbdkit plugin
> that was intended as a more sane replacement for vfat.  Since then
> several more nbdkit plugins have been added.  They support arbitrary
> sizes already.  The first one is the most direct replacement for vvfat
> (although it doesn't support writes to the backing directory, because
> that feature is insane).

Thanks for bringing that solution. I'll take a look though I'm not
sure it'll fit our needs. That insane feature is required for us... We
need ways to retrieve files generated by the binaries run within QEMU.
Moreover, we'll probably soon replace all that setup by some SSH
commands once we have implemented a few missing network devices (at
least the raspi4b one). But as I think those patches make vvfat block
a bit better, I still find them worth merging.
Nonetheless, I appreciate your feedback and will keep it in mind the
next time we have to deal with emulations without network devices.

Thanks,

> https://libguestfs.org/nbdkit-floppy-plugin.1.html
> https://libguestfs.org/nbdkit-iso-plugin.1.html
> https://libguestfs.org/nbdkit-linuxdisk-plugin.1.html
> https://libguestfs.org/nbdkit-tmpdisk-plugin.1.html
>
> Very easy to use from qemu as documented here:
>
> https://libguestfs.org/nbdkit-client.1.html#ATTACHING-NBD-DEVICES-TO-A-VIRTUAL-MACHINE
>
> Rich.
>
> --
> Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
> Read my programming and virtualization blog: http://rwmj.wordpress.com
> libguestfs lets you edit virtual machines.  Supports shell scripting,
> bindings from many languages.  http://libguestfs.org
>

On Wed, Sep 3, 2025 at 9:57 AM Clément Chigot <chigot@adacore.com> wrote:
>
> The main goal of this series is to introduce a new option "size" within
> the vvfat backend (patch 5). It allows more control over SD cards' size.
> The value for "Number of Heads" and "Sectors per track" are based on SD
> specifications Part 2.
>
> This series also includes minor patches:
>  - patch 1 introduces another option to remove the Master Boot Record
>    (this is mandatory for QNX)
>  - patch 2-4 are minor improvements easing the introducing of "size"
>    option
>
> This was tested on with a aarch64-linux kernel taken from
> functional/aarch64/test-virt and on aarch64-qnx over raspi4b with a
> workaround, not included here (the SD bus must be associated to the EMMC2
> port instead of through GPIOs).

Gentle ping for this series.

TIA
Clément

> Clément Chigot (5):
>   vvfat: introduce no-mbr option
>   vvfat: move fat_type check prior to size setup
>   vvfat: add a define for SECTOR_SIZE
>   vvfat: move size parameters within driver structure
>   vvfat: add support for "size" options
>
>  block/vvfat.c | 279 ++++++++++++++++++++++++++++++++++++++------------
>  1 file changed, 213 insertions(+), 66 deletions(-)
>
> --
> 2.34.1
>

On Wed, Sep 3, 2025 at 9:57 AM Clément Chigot <chigot@adacore.com> wrote:
>
> The main goal of this series is to introduce a new option "size" within
> the vvfat backend (patch 5). It allows more control over SD cards' size.
> The value for "Number of Heads" and "Sectors per track" are based on SD
> specifications Part 2.
>
> This series also includes minor patches:
>  - patch 1 introduces another option to remove the Master Boot Record
>    (this is mandatory for QNX)
>  - patch 2-4 are minor improvements easing the introducing of "size"
>    option
>
> This was tested on with a aarch64-linux kernel taken from
> functional/aarch64/test-virt and on aarch64-qnx over raspi4b with a
> workaround, not included here (the SD bus must be associated to the EMMC2
> port instead of through GPIOs).

Gentle ping for this series.

TIA
Clément

> Clément Chigot (5):
>   vvfat: introduce no-mbr option
>   vvfat: move fat_type check prior to size setup
>   vvfat: add a define for SECTOR_SIZE
>   vvfat: move size parameters within driver structure
>   vvfat: add support for "size" options
>
>  block/vvfat.c | 279 ++++++++++++++++++++++++++++++++++++++------------
>  1 file changed, 213 insertions(+), 66 deletions(-)
>
> --
> 2.34.1
>