To me, the proposed change seems to be heading in the wrong direction.
We should aim to support more sharing of valid, non-mbuf kernel data
(e.g., data loaned from struct bufs) with subsystems which expect
mbufs chains; not less sharing.

From that perspective, the test for ``can I modify the kernel storage
backing this mbuf in-place?''needs to be stricter (less inclusive),
not more inclusive, since such `sharing' may involve non-mbuf
references to the same underlying storage.



In message <1095691582.387358.14048.nullmailer@yamt.dyndns.org>,
YAMAMOTO Takashi writes:
>hi,
>
>i'd like to change M_READONLY like the following.
>there's no point to protect external storage if it isn't shared.
>eg. receive buffers for jumbo frame.
>
>YAMAMOTO Takashi
>

[... patch, elided]