[0/6] vmdk: Fix zero cluster handling

Message

Kevin Wolf April 30, 2020, 1:30 p.m. UTC

What I was really investigating is why 055 was so slow. I couldn't solve
that, but instead I found out that our VMDK code for zero clusters and
write_zeroes was completely broken. Apart from segfaults when zero
clusters were actually enabled, this caused a compressed backup target
to result in a bigger file than uncompressed with VMDK.

This series tries to fix it (with one bonus performance patch).

Kevin Wolf (6):
  vmdk: Rename VmdkMetaData.valid to new_allocation
  vmdk: Fix zero cluster allocation
  vmdk: Fix partial overwrite of zero cluster
  vmdk: Don't update L2 table for zero write on zero cluster
  vmdk: Flush only once in vmdk_L2update()
  iotests: vmdk: Enable zeroed_grained=on by default

 block/vmdk.c             | 47 +++++++++++++++++++++++++---------------
 tests/qemu-iotests/059   |  6 ++---
 tests/qemu-iotests/check |  3 +++
 3 files changed, 35 insertions(+), 21 deletions(-)

Comments

Kevin Wolf May 5, 2020, 9:42 a.m. UTC | #1

Am 30.04.2020 um 15:30 hat Kevin Wolf geschrieben:
> What I was really investigating is why 055 was so slow. I couldn't solve
> that, but instead I found out that our VMDK code for zero clusters and
> write_zeroes was completely broken. Apart from segfaults when zero
> clusters were actually enabled, this caused a compressed backup target
> to result in a bigger file than uncompressed with VMDK.
> 
> This series tries to fix it (with one bonus performance patch).

Thanks for the review, fixed up the commit messages and applied.

If you were curious about the VMDK terminology, I looked it up and the
basic terms translate to qcow2 like this:

* grain directory = L1 table
* grain table = L2 table
* grain = cluster

"zeroed-grain GTE (grain table entry)" is the exact term used in the
VMDK spec for what we would call a zero cluster in qcow2.

Kevin