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

From: "Cédric Le Goater" <clg@kaod.org>
To: Kevin Wolf <kwolf@redhat.com>, <qemu-block@nongnu.org>
Cc: peter.maydell@linaro.org, qemu-devel@nongnu.org,
	"Daniel P. Berrangé" <berrange@redhat.com>,
	"Xiang Zheng" <zhengxiang9@huawei.com>
Subject: Re: [PULL 03/38] pflash: Only read non-zero parts of backend image
Date: Mon, 6 Feb 2023 16:54:46 +0100	[thread overview]
Message-ID: <be61e573-1713-472c-899e-ac51b8a22345@kaod.org> (raw)
In-Reply-To: <20230120122633.84983-4-kwolf@redhat.com>

Hello,

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 :/

Thanks,

C.


@@ -39,7 +39,7 @@ static int blk_pread_nonzeroes(BlockBack
              return ret;
          }
          if (!(ret & BDRV_BLOCK_ZERO)) {
-            ret = bdrv_pread(bs->file, offset, bytes,
+            ret = blk_pread(blk, offset, bytes,
                               (uint8_t *) buf + offset, 0);
              if (ret < 0) {
                  return ret;

