Re: [dpdk-dev] The mbuf API needs some cleaning up

[Olivier Matz <olivier.matz@6wind.com>]

Hi Morten,

Thanks for the feedback.

On Mon, Jul 13, 2020 at 11:57:38AM +0200, Morten Brørup wrote:

> The MBUF library exposes some macros and constants without the RTE_ prefix. I
> propose cleaning up these, so better names get into the coming LTS release.

Yes, Thomas talked about it some time ago and he even drafted a patch to
fix it. We can target 20.11 for the changes, but I think we'll have to
keep a compat API until 21.11.

> The worst is:
> #define MBUF_INVALID_PORT UINT16_MAX
> 
> I say it's the worst because when we were looking for the official "invalid"
> port value for our application, we didn't find this one. (Probably because its
> documentation is wrong.)
>
> MBUF_INVALID_PORT is defined in rte_mbuf_core.h without any description, and
> in rte_mbuf.h, where it is injected between the rte_pktmbuf_reset() function
> and its description, so the API documentation shows the function's description
> for the constant, and no description for the function.

The one in rte_mbuf_core.h should be kept, with a documentation.

> I propose keeping it at a sensible location in rte_mbuf_core.h only, adding a description, and renaming it to:
> #define RTE_PORT_INVALID UINT16_MAX

I suggest RTE_MBUF_PORT_INVALID

> For backwards compatibility, we could add:
> /* this old name is deprecated */
> #define MBUF_INVALID_PORT RTE_PORT_INVALID
> 
> I also wonder why there are no compiler warnings about the double definition?

If the value is the same, the compiler won't complain.

> There are also the data buffer location constants:
> #define EXT_ATTACHED_MBUF    (1ULL << 61)
> and
> #define IND_ATTACHED_MBUF    (1ULL << 62)
> 
>
> There are already macros (with good names) for reading these, so
> simply adding the RTE_ prefix to these two constants suffices.

Some applications use it, we also need a compat here.

> And all the packet offload flags, such as:
> #define PKT_RX_VLAN          (1ULL << 0)
> 
>
> They are supposed to be used by applications, so I guess we should
> keep them unchanged for ABI stability reasons.

I propose RTE_MBUF_F_<name> for the mbuf flags.

> And the local macro:
> #define MBUF_RAW_ALLOC_CHECK(m) do { \
> 
> This might as well be an internal inline function:
> /* internal */
> static inline void
> __rte_mbuf_raw_alloc_check(const struct rte_mbuf *m)
> 

agree, I don't think a macro is mandatory here


Thanks,
Olivier


> Or we could keep it a macro and move it next to
> __rte_mbuf_sanity_check(), keeping it clear that it is only relevant when
> RTE_LIBRTE_MBUF_DEBUG is set. But rename it to lower case, similar to the
> __rte_mbuf_sanity_check() macro.
>
> 
> Med venlig hilsen / kind regards
> - Morten Brørup
>