Re: [dpdk-dev] [PATCH] acl: Fix RTE_ACL_RULE_SZ macro definition

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

From: Levend Sayar <levendsayar@gmail.com>
Sent: Tuesday, July 7, 2020 4:25 PM
To: Ananyev, Konstantin <konstantin.ananyev@intel.com>
Cc: dev@dpdk.org
Subject: Re: [PATCH] acl: Fix RTE_ACL_RULE_SZ macro definition

Sure.
I am really sorry for not being verbose enough.

From lib/librte_acl/rte_acl.h

#define RTE_ACL_RULE_DEF(name, fld_num) struct name {\
    struct rte_acl_rule_data data;               \
    struct rte_acl_field field[fld_num];         \
}

RTE_ACL_RULE_DEF(rte_acl_rule,);

When you put the definition in-place, above line means :

struct rte_acl_rule {
   struct rte_acl_rule_data data;
   struct rte_acl_field field[];
}

[KA] Yes.

There is another define to get the size of an acl rule such as

#define RTE_ACL_RULE_SZ(fld_num)    \
    (sizeof(struct rte_acl_rule) + sizeof(struct rte_acl_field) * (fld_num))

So the above definition gets the size of a "struct rte_acl_rule" which has fld_num fields.
which must be
sizeof (struct rte_acl_rule_data) + (sizeof(struct rte_acl_field) * fld_num)

Because it adds up the sizes of struct components;

[KA] I don’t think so.
You forgot about possible gaps between members of rte_acl_rule.
Let say for 64 bit target it would be a 4B gap between ‘data’ and ‘field’.
So, for:
RTE_ACL_RULE_DEF(xz, 1);

sizeof(struct xz) == RTE_ACL_RULE_SZ(1) == 32

After changes you suggest
RTE_ACL_RULE_SZ(1) == 28 != sizeof(struct xz)
Which is wrong.

But according to the current RTE_ACL_RULE_SZ, it is

sizeof (struct rte_acl_rule) + (sizeof(struct rte_acl_field) * fld_num)

So my patch only changes the part that I underlined.

sizeof (struct rte_acl_rule) = 16;
sizeof (struct rte_acl_rule_data) = 12;

Best,
Levend


On Tue, Jul 7, 2020 at 3:42 PM Ananyev, Konstantin <konstantin.ananyev@intel.com<mailto:konstantin.ananyev@intel.com>> wrote:

> From: Levend Sayar <levendsayar@gmail.com<mailto:levendsayar@gmail.com>>

Could you provide some explanation:
What do you think is wrong with current version and why,
and what your fix does.

>
> Signed-off-by: Levend Sayar <levendsayar@gmail.com<mailto:levendsayar@gmail.com>>
> ---
>  lib/librte_acl/rte_acl.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/lib/librte_acl/rte_acl.h b/lib/librte_acl/rte_acl.h
> index aa22e70c6..d34fdbc0e 100644
> --- a/lib/librte_acl/rte_acl.h
> +++ b/lib/librte_acl/rte_acl.h
> @@ -116,7 +116,7 @@ struct rte_acl_rule_data {
>  RTE_ACL_RULE_DEF(rte_acl_rule,);
>
>  #define      RTE_ACL_RULE_SZ(fld_num)        \
> -     (sizeof(struct rte_acl_rule) + sizeof(struct rte_acl_field) * (fld_num))
> +     (sizeof(struct rte_acl_rule_data) + sizeof(struct rte_acl_field) * (fld_num))
>
>
>  /** Max number of characters in name.*/
> --
> 2.27.0