[for-4.2?,0/6] block: Fix resize (extending) of short overlays

Message

Kevin Wolf Nov. 20, 2019, 2:03 p.m. UTC

Consider the following scenario where the overlay is shorter than its
backing file:

    base.qcow2:     AAAAAAAA
    overlay.qcow2:  BBBB

When resizing (extending) overlay.qcow2, the new blocks should not stay
unallocated and make the additional As from base.qcow2 visible like
before this series, but zeros should be read.

A similar case happens with the various variants of a commit job when an
intermediate file is short (- for unallocated):

    base.qcow2:     A-A-AAAA
    mid.qcow2:      BB-B
    top.qcow2:      C--C--C-

After commit top.qcow2 to mid.qcow2, the following happens:

    mid.qcow2:      CB-C00C0 (correct result)
    mid.qcow2:      CB-C--C- (before this fix)

Without the fix, blocks that previously read as zeros on top.qcow2
suddenly turn into A.

Kevin Wolf (6):
  block: bdrv_co_do_pwrite_zeroes: 64 bit 'bytes' parameter
  block: truncate: Don't make backing file data visible
  iotests: Add qemu_io_log()
  iotests: Fix timeout in run_job()
  iotests: Support job-complete in run_job()
  iotests: Test committing to short backing file

 block/io.c                    |  31 ++++++-
 tests/qemu-iotests/274        | 131 +++++++++++++++++++++++++++++
 tests/qemu-iotests/274.out    | 150 ++++++++++++++++++++++++++++++++++
 tests/qemu-iotests/group      |   1 +
 tests/qemu-iotests/iotests.py |  11 ++-
 5 files changed, 319 insertions(+), 5 deletions(-)
 create mode 100755 tests/qemu-iotests/274
 create mode 100644 tests/qemu-iotests/274.out

Comments

Vladimir Sementsov-Ogievskiy Nov. 20, 2019, 3:49 p.m. UTC | #1

20.11.2019 17:03, Kevin Wolf wrote:
> Consider the following scenario where the overlay is shorter than its
> backing file:
> 
>      base.qcow2:     AAAAAAAA
>      overlay.qcow2:  BBBB
> 
> When resizing (extending) overlay.qcow2, the new blocks should not stay
> unallocated and make the additional As from base.qcow2 visible like
> before this series, but zeros should be read.
> 
> A similar case happens with the various variants of a commit job when an
> intermediate file is short (- for unallocated):
> 
>      base.qcow2:     A-A-AAAA
>      mid.qcow2:      BB-B
>      top.qcow2:      C--C--C-
> 
> After commit top.qcow2 to mid.qcow2, the following happens:
> 
>      mid.qcow2:      CB-C00C0 (correct result)
>      mid.qcow2:      CB-C--C- (before this fix)
> 
> Without the fix, blocks that previously read as zeros on top.qcow2
> suddenly turn into A.

Note, that committing to base should still be broken after these series,
and is fixed in my "[PATCH 0/4] fix & merge block_status_above and is_allocated_above".

I think, I'll post a 5/4 patch, to add this case to your new test.

> 
> Kevin Wolf (6):
>    block: bdrv_co_do_pwrite_zeroes: 64 bit 'bytes' parameter
>    block: truncate: Don't make backing file data visible
>    iotests: Add qemu_io_log()
>    iotests: Fix timeout in run_job()
>    iotests: Support job-complete in run_job()
>    iotests: Test committing to short backing file
> 
>   block/io.c                    |  31 ++++++-
>   tests/qemu-iotests/274        | 131 +++++++++++++++++++++++++++++
>   tests/qemu-iotests/274.out    | 150 ++++++++++++++++++++++++++++++++++
>   tests/qemu-iotests/group      |   1 +
>   tests/qemu-iotests/iotests.py |  11 ++-
>   5 files changed, 319 insertions(+), 5 deletions(-)
>   create mode 100755 tests/qemu-iotests/274
>   create mode 100644 tests/qemu-iotests/274.out
>