Re: [PATCH v10 30/30] packet: Add support for multi-vector packets

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Aug 14, 2025 at 11:48:49AM +0200, Laurent Vivier wrote:
> The packet pool was previously limited to handling packets contained
> within a single buffer.
> 
> This patch extends the packet pool to support iovec array,
> allowing a single logical packet to be composed of multiple iovec.
> 
> To accommodate this, the storage format within the pool is modified.
> For a multi-vector packet, a header entry is now stored first with
> iov_base = NULL and iov_len holding the number of subsequent
> vectors. The actual data vectors are then stored in the following
> pool slots.
> 
> The packet_add_do() and packet_get_do() functions are updated to
> manage this new format for storing and retrieving packets. The
> pool_full() check is also adjusted to ensure there is enough
> space for all vectors of a new packet before adding it.
> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> ---
>  packet.c | 52 ++++++++++++++++++++++++++++++++++------------------
>  packet.h |  2 +-
>  tap.c    |  4 ++--
>  3 files changed, 37 insertions(+), 21 deletions(-)
> 
> diff --git a/packet.c b/packet.c
> index 27693c55a138..c88e726c94a6 100644
> --- a/packet.c
> +++ b/packet.c
> @@ -91,14 +91,15 @@ static int packet_check_range(const struct pool *p, const char *ptr, size_t len,
>  	return 0;
>  }
>  /**
> - * pool_full() - Is a packet pool full?
> + * pool_can_fit() - Is a new packet can fit in the pool?

"Can a new packet fit in the pool?"

>   * @p:		Pointer to packet pool
> + * @data:	check data can fit in the pool
>   *
> - * Return: true if the pool is full, false if more packets can be added
> + * Return: true if the pool is full, false if data can be added

With the name changed, the sense needs to be inverted as well.  Also
s/data/@data/ to make it clear we're talking specifically about the
parameter, not "data" in the broad sense.

>   */
> -bool pool_full(const struct pool *p)
> +bool pool_can_fit(const struct pool *p, const struct iov_tail *data)
>  {
> -	return p->count >= p->size;
> +	return p->count + data->cnt  + (data->cnt > 1) >= p->size;

Still an off-by-one here, see comments in the other thread.

..and this is still only valid if @data is already pruned.  I really
think a bunch of things would become a bit clearer if you add a change
earlier in the series clarifying that iov_tails should never be passed
around unpruned.

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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