Re: [PATCH for-5.0 v4 1/5] block: Add bdrv_qapi_perm_to_blk_perm()

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

08.11.2019 15:34, Max Reitz wrote:
> We need some way to correlate QAPI BlockPermission values with
> BLK_PERM_* flags.  We could:
> 
> (1) have the same order in the QAPI definition as the the BLK_PERM_*
>      flags are in LSb-first order.  However, then there is no guarantee
>      that they actually match (e.g. when someone modifies the QAPI schema
>      without thinking of the BLK_PERM_* definitions).
>      We could add static assertions, but these would break what’s good
>      about this solution, namely its simplicity.
> 
> (2) define the BLK_PERM_* flags based on the BlockPermission values.
>      But this way whenever someone were to modify the QAPI order
>      (perfectly sensible in theory), the BLK_PERM_* values would change.
>      Because these values are used for file locking, this might break
>      file locking between different qemu versions.
> 
> Therefore, go the slightly more cumbersome way: Add a function to
> translate from the QAPI constants to the BLK_PERM_* flags.
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>

Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

> ---
>   block.c               | 18 ++++++++++++++++++
>   include/block/block.h |  1 +
>   2 files changed, 19 insertions(+)
> 
> diff --git a/block.c b/block.c
> index 4cffc2bc35..066433f3e2 100644
> --- a/block.c
> +++ b/block.c
> @@ -2227,6 +2227,24 @@ void bdrv_format_default_perms(BlockDriverState *bs, BdrvChild *c,
>       *nshared = shared;
>   }
>   
> +uint64_t bdrv_qapi_perm_to_blk_perm(BlockPermission qapi_perm)
> +{
> +    static const uint64_t permissions[] = {
> +        [BLOCK_PERMISSION_CONSISTENT_READ]  = BLK_PERM_CONSISTENT_READ,
> +        [BLOCK_PERMISSION_WRITE]            = BLK_PERM_WRITE,
> +        [BLOCK_PERMISSION_WRITE_UNCHANGED]  = BLK_PERM_WRITE_UNCHANGED,
> +        [BLOCK_PERMISSION_RESIZE]           = BLK_PERM_RESIZE,
> +        [BLOCK_PERMISSION_GRAPH_MOD]        = BLK_PERM_GRAPH_MOD,
> +    };
> +
> +    QEMU_BUILD_BUG_ON(ARRAY_SIZE(permissions) != BLOCK_PERMISSION__MAX);
> +    QEMU_BUILD_BUG_ON(1UL << ARRAY_SIZE(permissions) != BLK_PERM_ALL + 1);

safe enough)

> +
> +    assert(qapi_perm < BLOCK_PERMISSION__MAX);
> +
> +    return permissions[qapi_perm];
> +}
> +
>   static void bdrv_replace_child_noperm(BdrvChild *child,
>                                         BlockDriverState *new_bs)
>   {
> diff --git a/include/block/block.h b/include/block/block.h
> index 1df9848e74..e9dcfef7fa 100644
> --- a/include/block/block.h
> +++ b/include/block/block.h
> @@ -280,6 +280,7 @@ enum {
>   };
>   
>   char *bdrv_perm_names(uint64_t perm);
> +uint64_t bdrv_qapi_perm_to_blk_perm(BlockPermission qapi_perm);
>   
>   /* disk I/O throttling */
>   void bdrv_init(void);
> 


-- 
Best regards,
Vladimir