debian/patches/extra/0006-block-io-Update-BSC-only-if-want_zero-is-true.patch

   1 From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
   2 From: Hanna Reitz <hreitz@redhat.com>
   3 Date: Tue, 18 Jan 2022 17:59:59 +0100
   4 Subject: [PATCH] block/io: Update BSC only if want_zero is true
   5
   6 We update the block-status cache whenever we get new information from a
   7 bdrv_co_block_status() call to the block driver.  However, if we have
   8 passed want_zero=false to that call, it may flag areas containing zeroes
   9 as data, and so we would update the block-status cache with wrong
  10 information.
  11
  12 Therefore, we should not update the cache with want_zero=false.
  13
  14 Reported-by: Nir Soffer <nsoffer@redhat.com>
  15 Fixes: 0bc329fbb00 ("block: block-status cache for data regions")
  16 Reviewed-by: Nir Soffer <nsoffer@redhat.com>
  17 Cc: qemu-stable@nongnu.org
  18 Signed-off-by: Hanna Reitz <hreitz@redhat.com>
  19 Message-Id: <20220118170000.49423-2-hreitz@redhat.com>
  20 Reviewed-by: Eric Blake <eblake@redhat.com>
  21 Signed-off-by: Eric Blake <eblake@redhat.com>
  22 ---
  23  block/io.c | 6 +++++-
  24  1 file changed, 5 insertions(+), 1 deletion(-)
  25
  26 diff --git a/block/io.c b/block/io.c
  27 index bb0a254def..4e4cb556c5 100644
  28 --- a/block/io.c
  29 +++ b/block/io.c
  30 @@ -2497,8 +2497,12 @@ static int coroutine_fn bdrv_co_block_status(BlockDriverState *bs,
  31               * non-protocol nodes, and then it is never used.  However, filling
  32               * the cache requires an RCU update, so double check here to avoid
  33               * such an update if possible.
  34 +             *
  35 +             * Check want_zero, because we only want to update the cache when we
  36 +             * have accurate information about what is zero and what is data.
  37               */
  38 -            if (ret == (BDRV_BLOCK_DATA | BDRV_BLOCK_OFFSET_VALID) &&
  39 +            if (want_zero &&
  40 +                ret == (BDRV_BLOCK_DATA | BDRV_BLOCK_OFFSET_VALID) &&
  41                  QLIST_EMPTY(&bs->children))
  42              {
  43                  /*