Re: [PATCH v2 12/36] block: refactor bdrv_child* permission functions

[Kevin Wolf <kwolf@redhat.com>]

Am 27.11.2020 um 15:44 hat Vladimir Sementsov-Ogievskiy geschrieben:
> Split out non-recursive parts, and refactor as block graph transaction
> action.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>  block.c | 79 ++++++++++++++++++++++++++++++++++++++++++---------------
>  1 file changed, 59 insertions(+), 20 deletions(-)
> 
> diff --git a/block.c b/block.c
> index a756f3e8ad..7267b4a3e9 100644
> --- a/block.c
> +++ b/block.c
> @@ -48,6 +48,7 @@
>  #include "qemu/timer.h"
>  #include "qemu/cutils.h"
>  #include "qemu/id.h"
> +#include "qemu/transactions.h"
>  #include "block/coroutines.h"
>  
>  #ifdef CONFIG_BSD
> @@ -2033,6 +2034,61 @@ static void bdrv_child_perm(BlockDriverState *bs, BlockDriverState *child_bs,
>      }
>  }
>  
> +static void bdrv_child_set_perm_commit(void *opaque)
> +{
> +    BdrvChild *c = opaque;
> +
> +    c->has_backup_perm = false;
> +}
> +
> +static void bdrv_child_set_perm_abort(void *opaque)
> +{
> +    BdrvChild *c = opaque;
> +    /*
> +     * We may have child->has_backup_perm unset at this point, as in case of
> +     * _check_ stage of permission update failure we may _check_ not the whole
> +     * subtree.  Still, _abort_ is called on the whole subtree anyway.
> +     */
> +    if (c->has_backup_perm) {
> +        c->perm = c->backup_perm;
> +        c->shared_perm = c->backup_shared_perm;
> +        c->has_backup_perm = false;
> +    }
> +}
> +
> +static TransactionActionDrv bdrv_child_set_pem_drv = {
> +    .abort = bdrv_child_set_perm_abort,
> +    .commit = bdrv_child_set_perm_commit,
> +};
> +
> +/*
> + * With tran=NULL needs to be followed by direct call to either
> + * bdrv_child_set_perm_commit() or bdrv_child_set_perm_abort().
> + *
> + * With non-NUll tran needs to be followed by tran_abort() or tran_commit()

s/NUll/NULL/

> + * instead.
> + */
> +static void bdrv_child_set_perm_safe(BdrvChild *c, uint64_t perm,
> +                                     uint64_t shared, GSList **tran)
> +{
> +    if (!c->has_backup_perm) {
> +        c->has_backup_perm = true;
> +        c->backup_perm = c->perm;
> +        c->backup_shared_perm = c->shared_perm;
> +    }

This is the obvious refactoring at this point, and it's fine as such.

However, when you start to actually use tran (and in new places), it
means that I have to check that we can never end up here recursively
with a different tran.

It would probably be much cleaner if the next patch moved the backup
state into the opaque struct for BdrvAction.

Kevin