On Sat, Jun 4, 2016 at 4:01 AM, joeyli <j...@suse.com> wrote: > Hi Dan, > > Thanks for your review. > > On Fri, Jun 03, 2016 at 12:27:34PM -0700, Dan Williams wrote: >> On Fri, Jun 3, 2016 at 12:13 AM, Lee, Chun-Yi <joeyli.ker...@gmail.com> >> 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 <j...@suse.com> >> > Cc: Gary Lin <g...@suse.com> >> > Cc: Dan Williams <dan.j.willi...@intel.com> >> > Cc: Ross Zwisler <ross.zwis...@linux.intel.com> >> > Cc: "Rafael J. Wysocki" <r...@rjwysocki.net> >> > --- >> > 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? > > Actually I didn't try to write SPA-VCD device before. Every time I mount it > that the system responses read-only: > > # mount /dev/pmem0 /mnt/ > mount: /dev/pmem0 is write-protected, mounting read-only > > If it can be written, then I think there have no difference between > NFIT_SPA_VOLATILE with NFIT_SPA_VCD region. > > I implemented this patch to treat VCD region as read-only pmem because the > pmem region generates /dev/pmem* device that it can be mounted. > > Maybe I missed. Does NFIT_SPA_VOLATILE region also generate a device in /dev > that it can be mounted with filesystem? Then I think treat the VCD region as > a read-only VOLATILE region that's also a solution.
My question is why does it need to be read-only? If it's a volatile region, does it matter if we allow writes at the block device level? Especially if it is formatted as iso9660, it won't be writable through the filesystem anyway.
