Re: [PATCH] libnvdimm, nfit: treat volatile virtual CD region as read-only pmem

[Dan Williams]

On Fri, Jun 3, 2016 at 12:13 AM, Lee, Chun-Yi <joeyli.kernel@xxxxxxxxx> wrote:
> This patch adds codes to treat a volatile virtual CD region as a
> read-only pmem region, then read-only /dev/pmem* device can be mounted
> with iso9660.
>
> It's useful to work with the httpboot in EFI firmware to pull a remote
> ISO file to the local memory region for booting and installation.
>
> Wiki page of UEFI HTTPBoot with OVMF:
>         https://en.opensuse.org/UEFI_HTTPBoot_with_OVMF
>
> Signed-off-by: Lee, Chun-Yi <jlee@xxxxxxxx>
> Cc: Gary Lin <GLin@xxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
> Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>
> ---
>  drivers/acpi/nfit.c          |  8 +++++++-
>  drivers/nvdimm/region_devs.c | 26 +++++++++++++++++++++++++-
>  include/linux/libnvdimm.h    |  2 ++
>  3 files changed, 34 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/acpi/nfit.c b/drivers/acpi/nfit.c
> index 2215fc8..b100a17 100644
> --- a/drivers/acpi/nfit.c
> +++ b/drivers/acpi/nfit.c
> @@ -1949,6 +1949,7 @@ static int acpi_nfit_init_mapping(struct acpi_nfit_desc *acpi_desc,
>         switch (nfit_spa_type(spa)) {
>         case NFIT_SPA_PM:
>         case NFIT_SPA_VOLATILE:
> +       case NFIT_SPA_VCD:
>                 nd_mapping->start = memdev->address;
>                 nd_mapping->size = memdev->region_size;
>                 break;

Why do we need to distinguish NFIT_SPA_VOLATILE vs NFIT_SPA_VCD, i.e.
what happens if something writes to a VCD device?