Re: [PULL 03/38] pflash: Only read non-zero parts of backend image

[Cédric Le Goater]

On 2/7/23 09:38, Kevin Wolf wrote:
> Am 06.02.2023 um 16:54 hat Cédric Le Goater geschrieben:
> > On 1/20/23 13:25, Kevin Wolf wrote:
> > > From: Xiang Zheng <zhengxiang9@huawei.com>
> > >
> > > Currently we fill the VIRT_FLASH memory space with two 64MB NOR images
> > > when using persistent UEFI variables on virt board. Actually we only use
> > > a very small(non-zero) part of the memory while the rest significant
> > > large(zero) part of memory is wasted.
> > >
> > > So this patch checks the block status and only writes the non-zero part
> > > into memory. This requires pflash devices to use sparse files for
> > > backends.
> > >
> > > Signed-off-by: Xiang Zheng <zhengxiang9@huawei.com>
> > >
> > > [ kraxel: rebased to latest master ]
> > >
> > > Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> > > Message-Id: <20221220084246.1984871-1-kraxel@redhat.com>
> > > Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
> > > Reviewed-by: Kevin Wolf <kwolf@redhat.com>
> > > Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> >
> > This newly merged patch introduces a "regression" when booting an Aspeed
> > machine. The following extra m25p80 patch (not yet merged) is required
> > for the issue to show:
> >
> >    https://lore.kernel.org/qemu-devel/20221115151000.2080833-1-clg@kaod.org/
> >
> > U-Boot fails to find the filesystem in that case.
> >
> > It can be easily reproduced with the witherspoon-bmc machine and seems
> > to be related to the use of a UBI filesystem. Other Aspeed machines not
> > using UBI are not impacted.
> >
> > Here is a tentative fix. I don't know enough the block layer to explain
> > what is happening :/
>
> I was puzzled for a moment, but...
>
> > @@ -39,7 +39,7 @@ static int blk_pread_nonzeroes(BlockBack
> >               return ret;
> >           }
> >           if (!(ret & BDRV_BLOCK_ZERO)) {
> > -            ret = bdrv_pread(bs->file, offset, bytes,
>
> 'bs->file' rather than 'bs' really looks wrong. I think replacing that
> would already fix the bug you're seeing.
>
> Just to be sure, how did you configure the block backend? bs->file would
> happen to work more or less with raw over file-posix (which is probably
> what Gerd tested), but I think it breaks with anything else.

The command is  :

  $ qemu-system-arm -M witherspoon-bmc -net user \
        -drive file=/path/to/file.mtd,format=raw,if=mtd \
        -nographic -serial mon:stdio -snapshot

If I remove '-snapshot', all works fine.

Here is a file :

  
https://jenkins.openbmc.org/job/ci-openbmc/distro=ubuntu,label=docker-builder,target=witherspoon/lastSuccessfulBuild/artifact/openbmc/build/tmp/deploy/images/witherspoon/obmc-phosphor-image-witherspoon-20230207051412.ubi.mtd

Thanks,

C.

> > +            ret = blk_pread(blk, offset, bytes,
> >                                (uint8_t *) buf + offset, 0);
>
> blk_*() makes even more sense conceptually, but it should behave the
> same.
>
> Kevin