Re: [Qemu-devel] [PATCH 0/6] block: Fix permissions after ro/rw reopen

[Fam Zheng <famz@redhat.com>]

On Fri, 09/15 12:10, Kevin Wolf wrote:
> bdrv_reopen() can switch nodes between read-only and read-write modes.
> This has implications for the required permissions on their child nodes.
> For example, a qcow2 node requests write permissions on bs->file only if
> it is writable itself.
> 
> This means that during bdrv_reopen(), the permissions need to be
> recalculated in order to prevent failures where the bs->file
> permissions don't match its actual read-only state (e.g. bs->file is a
> read-write node, but the permission still enforces read-only access).

Passing reopen_queue around makes the interface and implementations complicated.
I wonder if any of the alternatives make sense:

1) Don't pass reopen_queue as a parameter, just pass the one interesting
BDRVReopenState pointer. So that callees don't need to call
bdrv_reopen_get_flags().

2) Don't change the prototypes at all, just change .bdrv_reopen_prepare contract
so that after it returns, .bdrv_child_perm/.bdrv_check_perm should comply to the
new state that would be commited once .bdrv_reopen_commit() is called, or
reverted if .bdrv_reopen_abort().

3) Don't change the prototypes at all, track the reopen progress in block.c
generically, (e.g. ignore conflicts and voilations) and update the permissions
only after bdrv_reopen_commit().

Fam

> 
> Kevin Wolf (6):
>   qemu-io: Reset qemuio_blk permissions before each command
>   block: Add reopen_queue to bdrv_child_perm()
>   block: Add reopen queue to bdrv_check_perm()
>   block: Base permissions on rw state after reopen
>   block: reopen: Queue children after their parents
>   block: Fix permissions after bdrv_reopen()
> 
>  include/block/block.h      |   2 +-
>  include/block/block_int.h  |   7 ++
>  block.c                    | 191 +++++++++++++++++++++++++++++++++------------
>  block/commit.c             |   1 +
>  block/mirror.c             |   1 +
>  block/replication.c        |   1 +
>  block/vvfat.c              |   1 +
>  qemu-io.c                  |  13 +++
>  tests/qemu-iotests/187.out |   2 +-
>  9 files changed, 169 insertions(+), 50 deletions(-)
> 
> -- 
> 2.13.5
>