Hi Maxime,
On 09/29/2016 02:20 PM, Maxime Coquelin wrote:
> Some application use rte_mbuf_raw_alloc() function to improve
> performance by not resetting mbuf's fields to their default state.
>
> This can be however problematic for mbuf consumers that need some
> headroom, meaning that data_off field gets decremented after
> allocation. When the mbuf is re-used afterwards, there might not
> be enough room for the consumer to prepend anything, if the data_off
> field is not reset to its default value.
>
> This patch adds a new rte_pktmbuf_reset_headroom() function that
> applications can call to reset the data_off field.
> This patch also replaces current data_off affectations in the mbuf
> lib with a call to this function.
>
> Signed-off-by: Maxime Coquelin <maxime.coquelin at redhat.com>
Sounds like a good idea. Just one small comment below.
>
> /**
> + * Reset the data_off field of a packet mbuf to its default value.
> + *
> + * The given mbuf must have only one segment.
> + *
> + * @param m
> + * The packet mbuf's data_off field has to be reset.
> + */
> +static inline void rte_pktmbuf_reset_headroom(struct rte_mbuf *m)
> +{
> + m->data_off = RTE_MIN(RTE_PKTMBUF_HEADROOM, (uint16_t)m->buf_len);
> +}
Maybe we should also highlight in the API comment that the segment
should be empty.
Thanks,
Olivier
