netdev - What does this code do

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Date:   Tue, 10 Mar 2020 14:42:11 -0700
From:   Andrej Ras <kermitthekoder@...il.com>
To:     netdev@...r.kernel.org
Subject: What does this code do

While browsing the Linux networking code I came across these two lines
in __ip_append_data() which I do not understand.

                /* Check if the remaining data fits into current packet. */
                copy = mtu - skb->len;
                if (copy < length)
                        copy = maxfraglen - skb->len;
                if (copy <= 0) {

Why not just use maxfraglen.

Perhaps someone can explain why this is needed.

Regards