Re: [Qemu-devel] [Qemu-block] [PATCH for-2.10 2/5] block: Allow reopen rw without BDRV_O_ALLOW_RDWR

[Jeff Cody <jcody@redhat.com>]

On Thu, Aug 03, 2017 at 05:02:58PM +0200, Kevin Wolf wrote:
> BDRV_O_ALLOW_RDWR is a flag that tells whether qemu can internally
> reopen a node read-write temporarily because the user requested
> read-write for the top-level image, but qemu decided that read-only is
> enough for this node (a backing file).
> 
> bdrv_reopen() is different, it is also used for cases where the user
> changed their mind and wants to update the options. There is no reason
> to forbid making a node read-write in that case.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  include/block/block.h |  3 ++-
>  block.c               | 11 +++++++----
>  2 files changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/include/block/block.h b/include/block/block.h
> index 34770bb33a..ab80195378 100644
> --- a/include/block/block.h
> +++ b/include/block/block.h
> @@ -436,7 +436,8 @@ int bdrv_is_allocated_above(BlockDriverState *top, BlockDriverState *base,
>  
>  bool bdrv_is_read_only(BlockDriverState *bs);
>  bool bdrv_is_writable(BlockDriverState *bs);
> -int bdrv_can_set_read_only(BlockDriverState *bs, bool read_only, Error **errp);
> +int bdrv_can_set_read_only(BlockDriverState *bs, bool read_only,
> +                           bool ignore_allow_rdw, Error **errp);
>  int bdrv_set_read_only(BlockDriverState *bs, bool read_only, Error **errp);
>  bool bdrv_is_sg(BlockDriverState *bs);
>  bool bdrv_is_inserted(BlockDriverState *bs);
> diff --git a/block.c b/block.c
> index ab908cdc50..2711c3dd3b 100644
> --- a/block.c
> +++ b/block.c
> @@ -246,7 +246,8 @@ bool bdrv_is_writable(BlockDriverState *bs)
>      return !bdrv_is_read_only(bs) && !(bs->open_flags & BDRV_O_INACTIVE);
>  }
>  
> -int bdrv_can_set_read_only(BlockDriverState *bs, bool read_only, Error **errp)
> +int bdrv_can_set_read_only(BlockDriverState *bs, bool read_only,
> +                           bool ignore_allow_rdw, Error **errp)

I think 'override_allow_rdw' may be a bit clearer, but that is just
bikeshedding.

Reviewed-by: Jeff Cody <jcody@redhat.com>


>  {
>      /* Do not set read_only if copy_on_read is enabled */
>      if (bs->copy_on_read && read_only) {
> @@ -256,7 +257,9 @@ int bdrv_can_set_read_only(BlockDriverState *bs, bool read_only, Error **errp)
>      }
>  
>      /* Do not clear read_only if it is prohibited */
> -    if (!read_only && !(bs->open_flags & BDRV_O_ALLOW_RDWR)) {
> +    if (!read_only && !(bs->open_flags & BDRV_O_ALLOW_RDWR) &&
> +        !ignore_allow_rdw)
> +    {
>          error_setg(errp, "Node '%s' is read only",
>                     bdrv_get_device_or_node_name(bs));
>          return -EPERM;
> @@ -269,7 +272,7 @@ int bdrv_set_read_only(BlockDriverState *bs, bool read_only, Error **errp)
>  {
>      int ret = 0;
>  
> -    ret = bdrv_can_set_read_only(bs, read_only, errp);
> +    ret = bdrv_can_set_read_only(bs, read_only, false, errp);
>      if (ret < 0) {
>          return ret;
>      }
> @@ -2907,7 +2910,7 @@ int bdrv_reopen_prepare(BDRVReopenState *reopen_state, BlockReopenQueue *queue,
>       * to r/w. Attempting to set to r/w may fail if either BDRV_O_ALLOW_RDWR is
>       * not set, or if the BDS still has copy_on_read enabled */
>      read_only = !(reopen_state->flags & BDRV_O_RDWR);
> -    ret = bdrv_can_set_read_only(reopen_state->bs, read_only, &local_err);
> +    ret = bdrv_can_set_read_only(reopen_state->bs, read_only, true, &local_err);
>      if (local_err) {
>          error_propagate(errp, local_err);
>          goto error;
> -- 
> 2.13.3
> 
>