[Qemu-devel] [PATCH 0/3] block: Make various formats' block_status recurse again

[Max Reitz]

Hi,

69f47505ee66afaa513305de0c1895a224e52c45 changed block_status so that it
would only go down to the protocol layer if the format layer returned
BDRV_BLOCK_RECURSE, thus indicating that it has no sufficient
information whether a given range in the image is zero or not.
Generally, this is because the image is preallocated and thus all ranges
appear as zeroes.

However, it only implemented this preallocation detection for qcow2.
There are more formats that support preallocation, though: vdi, vhdx,
vmdk, vpc.  (Funny how they all start with “v”.)

For vdi, vmdk, and vpc, the fix is rather simple, because they really
have different subformats depending on whether an image is preallocated
or not.  This makes the check very simple.

vhdx is more like qcow2, where after the image has been created, it
isn’t clear whether it’s been preallocated or everything is allocated
because everything was already written to.  69f47505ee added a heuristic
to qcow2 to get around this, but I think that’s too much for vhdx.  I
just left it unfixed, because I don’t care that much, honestly (and I
don’t think anyone else does).


Max Reitz (3):
  vdi: Make block_status recurse for fixed images
  vmdk: Make block_status recurse for flat extents
  vpc: Do not return RAW from block_status

 block/vdi.c  | 3 ++-
 block/vmdk.c | 3 +++
 block/vpc.c  | 2 +-
 3 files changed, 6 insertions(+), 2 deletions(-)

-- 
2.21.0