Re: [PATCH net v3 1/2] ipv4: account for fraggap on the paged allocation path

[Ido Schimmel <idosch@nvidia.com>]

On Thu, Jun 11, 2026 at 10:32:39PM +0900, Wongi Lee wrote:
> In __ip_append_data(), when the paged-allocation branch is taken,
> alloclen and pagedlen are computed as
> 
> 	alloclen = fragheaderlen + transhdrlen;
> 	pagedlen = datalen - transhdrlen;
> 
> datalen already includes fraggap, but the fraggap bytes carried over
> from the previous skb are copied into the new skb's linear area at
> offset transhdrlen by the subsequent skb_copy_and_csum_bits(). The
> linear area is therefore undersized by fraggap bytes while pagedlen is
> overstated by the same amount.
> 
> The non-paged branch sets alloclen to fraglen, which already accounts
> for fraggap because datalen does. Bring the paged branch in line by
> adding fraggap to alloclen and subtracting it from pagedlen.
> 
> After this adjustment, copy no longer collapses to -fraggap on the
> paged path, so remove the stale comment describing that old arithmetic.
> 
> Fixes: 8eb77cc73977 ("ipv4: avoid partial copy for zc")
> Signed-off-by: Jungwoo Lee <jwlee2217@gmail.com>
> Signed-off-by: Wongi Lee <qw3rtyp0@gmail.com>

Reviewed-by: Ido Schimmel <idosch@nvidia.com>