MTD: How to get actual image size from MTD partition

[Ezequiel Garcia]

On Mon, 8 Nov 2021 at 10:51, Pintu Agarwal <pintu.ping at gmail.com> wrote:
>
> Hi,
>
>
> On Fri, 29 Oct 2021 at 22:18, Ezequiel Garcia
> <ezequiel at vanguardiasur.com.ar> wrote:
> >
> > On Fri, 29 Oct 2021 at 13:13, Pintu Agarwal <pintu.ping at gmail.com> wrote:
> > >
> > > Hi All,
> > >
> > > On Mon, 30 Aug 2021 at 21:28, Pintu Agarwal <pintu.ping at gmail.com> wrote:
> > > >
> > > > On Sun, 22 Aug 2021 at 19:51, Ezequiel Garcia
> > > > <ezequiel at vanguardiasur.com.ar> wrote:
> > > >
> > > > > In other words, IMO it's best to expose the NAND through UBI
> > > > > for both read-only and read-write access, using a single UBI device,
> > > > > and then creating UBI volumes as needed. This will allow UBI
> > > > > to spread wear leveling across the whole device, which is expected
> > > > > to increase the flash lifetime.
> > > > >
> > > > > For instance, just as some silly example, you could have something like this:
> > > > >
> > > > >                                | RootFS SquashFS  |
> > > > >                                | UBI block        | UBIFS User R-W area
> > > > > ------------------------------------------------------------------------
> > > > > Kernel A | Kernel B | RootFS A | RootFS B         | User
> > > > > ------------------------------------------------------------------------
> > > > >                                  UBIX
> > > > > ------------------------------------------------------------------------
> > > > >                                  /dev/mtdX
> > > > >
> > > > > This setup allows safe kernel and rootfs upgrading. The RootFS is read-only
> > > > > via SquashFS and there's a read-write user area. UBI is supporting all
> > > > > the volumes, handling bad blocks and wear leveling.
> > > > >
> > > > Dear Ezequiel,
> > > > Thank you so much for your reply.
> > > >
> > > > This is exactly what we are also doing :)
> > > > In our system we have a mix of raw and ubi partitions.
> > > > The ubi partitioning is done almost exactly the same way.
> > > > Only for the rootfs (squashfs) I see we were using /mtd/block<id> to
> > > > mount the rootfs.
> > > > Now, I understood we should change it to use /dev/ubiblock<id>
> > > > This might have several benefits, but one most important could be,
> > > > using ubiblock can handle bad-blocks/wear-leveling automatically,
> > > > whereas mtdblocks access the flash directly ?
> > > > I found some references for these..
> > > > So, this seems good for my proposal.
> > > >
> > > > Another thing that is still open for us is:
> > > > How do we calculate the exact image size from a raw mtd partition ?
> > > > For example, support for one of the raw nand partitions, the size is
> > > > defined as 15MB but we flash the actual image of size only 2.5MB.
> > > > So, in the runtime how to determine the image size as ~2.5MB (at least
> > > > roughly) ?
> > > > Is it still possible ?
> > > >
> > >
> > > I am happy to inform you that using "ubiblock" for squashfs mounting
> > > seems very helpful for us.
> > > We have seen almost the double performance boost when using ubiblock
> > > for rootfs as well as other read-only volume mounting.
> > >
> > > However, we have found few issues while defining the read only volume as STATIC.
> > > With static volume we see that OTA update is failing during "fsync".
> > > That is ota_fsync is failing from here:
> > > https://gerrit.pixelexperience.org/plugins/gitiles/bootable_recovery/+/ff6df890a2a01bf3bf56d3f430b17a5ef69055cf%5E%21/otafault/ota_io.cpp
> > > int status = fsync(fd);
> > > if (status == -1 && errno == EIO)
> > > *
> > > { have_eio_error = true; }
> > > *
> > > return status;
> > > }
> > >
> > > Is this the known issue with static volume?
> > >
> >
> > I don't know exactly how you are updating your volume,
> > the right way is using UBI_IOCVOLUP.
> >
> > See http://www.linux-mtd.infradead.org/doc/ubi.html#L_volupdate
> >
> > If you google around I'm sure you'll find some articles about this,
> > but I'm not sure if they'll go into details and subtleties.
> >
> > There are probably a few different ways to do firmware upgrade
> > when you are on top of static volumes (and you want to be on top
> > of static volumes if it's read-only, because AFAIK they give you an
> > extra data-integrity guarantee).
> >
> > One way, would be to have two static volumes A/B. The system
> > uses normally the A volume, and then you doUBI_IOCVOLUP
> > (or ubiupdatevol) to update the B volume. After the update is succesful
> > you run the atomic volume rename and flip A->B, B->A.
> >
> > (If you don't have enough space to hold two A/B volumes....
> >  ... you'll have to find some other solution, I have no idea about that.)
> >
>
> Yes, this is what we are also doing exactly.
> But, currently we are running into this issue right now:
> 1) The FOTA update is failing if we use static volume (building and
> flashing the static image is fine)

Please add traces to find what syscall is failing, and provide more
details about it.

Thanks,
Ezequiel